Difference between revisions of "Team:UESTC-China/Demonstrate"

 
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<img src="https://static.igem.org/mediawiki/2018/7/7d/T--UESTC-China--up.png" width="100%">
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<a href="#" class="dropdown-toggle" data-toggle="dropdown">PROJECT</a>
 
<a href="#" class="dropdown-toggle" data-toggle="dropdown">PROJECT</a>
 
<ul class="dropdown-menu animated fadeOutUp">
 
<ul class="dropdown-menu animated fadeOutUp">
<li><a href="https://2018.igem.org/Team:UESTC-China/project_introduction">Introduction</a></li>
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<li><a href="https://2018.igem.org/Team:UESTC-China/Description">Description</a></li>
<li><a href="https://2018.igem.org/Team:UESTC-China/project_design">Design</a></li>
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<li><a href="https://2018.igem.org/Team:UESTC-China/Design">Design</a></li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/Demonstrate">Demonstrate</a></li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/Demonstrate">Demonstrate</a></li>
                                                                         <li><a href="https://2018.igem.org/Team:UESTC-China/Improve">Improve</a></li>
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</ul>
 
</ul>
 
</li>
 
</li>
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<a href="#" class="dropdown-toggle" data-toggle="dropdown">PART</a>
 
<a href="#" class="dropdown-toggle" data-toggle="dropdown">PART</a>
 
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<ul class="dropdown-menu animated fadeOutUp">
<li><a href="https://2018.igem.org/Team:UESTC-China/Part">Part</a></li>
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<li><a href="https://2018.igem.org/Team:UESTC-China/Parts">Basic Part</a></li>
<li><a href="https://2018.igem.org/Team:UESTC-China/Improve">Improve</a></li>
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<li><a href="https://2018.igem.org/Team:UESTC-China/Improve">Improve Part</a></li>
 
                                                                 </ul>   
 
                                                                 </ul>   
 
        </li>
 
        </li>
<li><a href="https://2018.igem.org/Team:UESTC-China/Model">MODELING</a></li>
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<li class="dropdown">
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<a href="#" class="dropdown-toggle" data-toggle="dropdown">MODEL</a>
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<ul class="dropdown-menu animated fadeOutUp">
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<li><a href="https://2018.igem.org/Team:UESTC-China/Model">Overview</a></li>
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<li><a href="https://2018.igem.org/Team:UESTC-China/Model_butanol">Butanol System Model</a></li>
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                                                                        <li><a href="https://2018.igem.org/Team:UESTC-China/Model_h2">Hydrogen System Model</a></li>
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</ul>
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</li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/Attributions">ATTRIBUTIONS</a></li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/Attributions">ATTRIBUTIONS</a></li>
 
<li class="dropdown">
 
<li class="dropdown">
 
<a href="#" class="dropdown-toggle" data-toggle="dropdown">H&nbsp;&nbsp;P</a>
 
<a href="#" class="dropdown-toggle" data-toggle="dropdown">H&nbsp;&nbsp;P</a>
 
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<ul class="dropdown-menu animated fadeOutUp">
<li><a href="https://2018.igem.org/Team:UESTC-China/hp_ourstory">Our Story</a></li>
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<li><a href="https://2018.igem.org/Team:UESTC-China/Human_Practice">Supporting Research</a></li>
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<li><a href="https://2018.igem.org/Team:UESTC-China/Human_Practices">Integrate Human Practice</a></li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/Public_Engagement">Engagement</a></li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/Public_Engagement">Engagement</a></li>
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                                                                        <li><a href="https://2018.igem.org/Team:UESTC-China/Software">Gene Card Online</a></li>
 
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</ul>
 
</li>
 
</li>
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<a href="#" class="dropdown-toggle" data-toggle="dropdown">NOTEBOOK</a>
 
<a href="#" class="dropdown-toggle" data-toggle="dropdown">NOTEBOOK</a>
 
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<ul class="dropdown-menu animated fadeOutUp">
<li><a href="https://2018.igem.org/Team:UESTC-China/notebook_daynote">Day Note</a></li>
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<li><a href="https://2018.igem.org/Team:UESTC-China/Notebook">Day Note</a></li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/notebook_protocol">Protocol</a></li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/notebook_protocol">Protocol</a></li>
<li><a href="https://2018.igem.org/Team:UESTC-China/notebook_safety">Safety</a></li>
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<li><a href="https://2018.igem.org/Team:UESTC-China/Safety">Safety</a></li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/InterLab">Interlab</a></li>
 
<li><a href="https://2018.igem.org/Team:UESTC-China/InterLab">Interlab</a></li>
 
</ul>
 
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     </div>
 
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     <div class="neirong" style="position:relative; z-index:1 ;padding:50px 8% 50px 1%; background-color:#fff">
 
<div class="row member">
 
<div class="row member">
  
 
<div class="col-md-3 col-sm-4">
 
<div class="col-md-3 col-sm-4">
                     <div class="fixed" style="position:fixed; top:250px; ">
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                     <div class="fixed" style="position:fixed; top:150px; ">
 
                         <div class="fl_l"><h3>Demonstrate</h3></div>
 
                         <div class="fl_l"><h3>Demonstrate</h3></div>
 
<menu id="tocc" class="hide-on-med-and-down" style="padding: 0.1px; left: 0px; z-index:1; font-family:'Candara',sans-serif;">
 
<menu id="tocc" class="hide-on-med-and-down" style="padding: 0.1px; left: 0px; z-index:1; font-family:'Candara',sans-serif;">
 
                                
 
                                
<ul class="fl_l" style="margin-top:200px; opacity:0;">
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<ul class="fl_l" style="margin-top:200px; opacity:0;
<li><a href="#">Pathway construction</a></li>
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<li><a href="#">Three pathway validation</a></li>
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max-width: 350px;">
<li><a href="#">Work going on</a></li>
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<li><a href="#">1.&nbsp;Pathway construction</a></li>
<li><a href="#">Reference</a></li>
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<li><a href="#">2.&nbsp;From straw to glucose</a></li>
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<li><a href="#">3.&nbsp;Butanol production</a></li>
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<li><a href="#">4.&nbsp;Hydrogen production</a></li>
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<li><a href="#">5.&nbsp;Work going on</a></li>
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<li><a href="#">6.&nbsp;References</a></li>
 
</ul>
 
</ul>
 
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<div class="main col-md-9 col-sm-8 col-xs-12">
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<div class="main col-md-9 col-sm-8 col-xs-12" style="padding-left:80px;">
  
 
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<ul class="fl_r">
 
<li>
 
<li>
 
         <div class="bigtitle">
 
         <div class="bigtitle">
             Pathway construction
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             1. Pathway construction
 
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         <div class="zhengwen">
 
         <div class="zhengwen">
             In order to express multiple enzymes in E. coli, we firstly did the codon-optimized of the enzymes. And then these genes were commercially synthesized. Finally, with the application of Gibson Assembly and Golden Gate strategy, we successfully introduced the target gene into different E. coli expression vector. (Fig. 1)
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             For efficient expression of multiple enzymes in <i>E. coli</i>, codon optimization of all target genes were performed before DNA synthesis. The obtained genes were subsequently cloned into different expression vectors by using Gibson Assembly and Golden Gate strategies. The resulting vectors piGEM2018-Module001, piGEM2018-Module002, and piGEM2018-Module003 are listed in Table 1.
 
         </div>
 
         </div>
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        <div class="xstitle">Table 1&nbsp;&nbsp;&nbsp;Illustration of the three constructed vectors.</div>
 
         <div class="zhengwen">
 
         <div class="zhengwen">
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 +
       
 +
       
 
             <table class="table table-hover">
 
             <table class="table table-hover">
                 <tr><td>No.</td><td> Vector </td><td>E.coli resistance </td><td>Vector map </td><td>Description</td></tr>
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                 <tr><td>No.</td><td> Vector </td><td><i>E. coli</i> resistance</td><td> Description</td></tr>
                 <tr><td>1 </td><td>piGEM2018-Module004</td><td> Amp </td><td> </td><td>BBa_J23100-RBS-pelB+5D-Xyn10D-fae1A-RBS-pelB+5D-Xyl3A-RBS-pelB+5D-cex-RBS-pelB+5D-cenA-Ter</td></tr>
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                 <tr><td>1</td><td> piGEM2018-Module001</td><td> Amp </td><td>BBa_J23100-RBS-pelB+5D-Xyn10D-Fae1A-RBS-pelB+5D-Xyl3A-RBS-pelB+5D-Cex-RBS-pelB+5D-CenA-Ter</td></tr>
                 <tr><td>2 </td><td>piGEM2018-Module002 </td><td>Kan </td><td></td><td> Ter-Ter-RBS-Fdh-RBS-FRE_adhE-FRE_ackA-RBS-AtoB-RBS-AdhE2-RBS-Crt-RBS-Hbd-Ter</td></tr>
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                 <tr><td>2</td><td> piGEM2018-Module002 </td><td>Kan </td><td>Ter-Ter-RBS-Fdh-RBS-FRE_adhE-FRE_ackA-RBS-AtoB-RBS-AdhE2-RBS-Crt-RBS-Hbd-Ter</td></tr>
                 <tr><td>3 </td><td>piGEM2018-Module003 </td><td>Kan </td><td></td><td> BBa_J23100-RBS-FhlA-RBS-HydA-Ter</td></tr>
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                 <tr><td>3 </td><td>piGEM2018-Module003 </td><td>Kan </td><td>BBa_J23100-RBS-FhlA-RBS-HydA-Ter</td></tr>
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             </table>
 
             </table>
 
         </div>
 
         </div>
        <div class="tu">Figure 1.&nbsp;The introduction of piGEM2018-Module001 to piGEM2018-Module003.</div>
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         <div class="zhengwen">
 
         <div class="zhengwen">
             Before DNA sequencing, those vectors were verified by restriction enzyme digestion. After electrophoresis analysis, the samples which contained all desired bands were selected and sent for sequencing. The sequencing results showed that all the above constructed vectors were successful. (Fig. 2)
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             Before DNA sequencing, those vectors were verified by restriction enzyme digestion. After electrophoresis analysis, the samples which contained the desired bands were selected and sent for sequencing. The sequencing results showed that all the above constructed vectors were successful. (Fig. 1)
 
         </div>
 
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         <div class="chatu" style="padding:20px 10%;"><img src="2" width="100%"></div>
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         <div class="chatu" style="padding:20px 0%;"><img src="https://static.igem.org/mediawiki/2018/f/fe/T--UESTC-China--dem2.png" width="100%"></div>
         <div class="tu">Figure 2.&nbsp; The image of agarose gel electrophoresis by double enzyme digestion.</div>
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         <div class="tu">
         <div class="tu">(a)piGEM2018-Module001 (Line1,enzyme digested by EcoR32Ⅰ+NcoⅠ; Line2,enzyme digested by NcoIⅠ+XhoⅠ)</div>
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            Fig. 1 Double restriction enzyme digestion of three constructed vectors analyzed by using agarose gel electrophoresis.  
         <div class="tu">(b) piGEM2018-Module002 (Line1,enzyme digested by PstⅠ+KpnⅠ; Line2,enzyme digested by HindⅢ+KpnⅠ)</div>
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        </div>
         <div class="tu">(c)piGEM2018-Module003 (Line1,enzyme digested by EcoRⅠ+NcoⅠ;Line2, enzyme digested by BamHⅠ+BglⅡ)</div>
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         <div class="tu">(a) piGEM2018-Module001 digested by <i>Eco32</i>Ⅰ+<i>Nco</i>Ⅰ(lane 1), piGEM2018-Module001 digested by <i>Nco</i>Ⅰ+<i>Xho</i>Ⅰ(lane 2); </div>
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         <div class="tu">(b) piGEM2018-Module002 digested by <i>Pst</i>Ⅰ+<i>Kpn</i>Ⅰ(lane 1), piGEM2018-Module002 digested by <i>Hind</i>Ⅲ+<i>Kpn</i>Ⅰ(lane 2); </div>
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         <div class="tu">(c) piGEM2018-Module003 digested by <i>EcoR</i>Ⅰ+<i>Nco</i>Ⅰ(lane 1), piGEM2018-Module003 digested by <i>BamH</i>Ⅰ+<i>Bgl</i>Ⅱ(lane 2).</div>
  
 
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     </li>
 
     <li>
 
     <li>
 
         <div class="bigtitle">
 
         <div class="bigtitle">
             Three pathway validation
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             2. From straw to glucose
        </div>
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        <div class="smtitle">
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            Straw degradation and glucose production
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         <div class="zhengwen">
 
         <div class="zhengwen">
             Xylanase can decompose xylan to xylose, and the activity of xylanase can be estimated by detecting the concentration of xylose.
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             <i>E. coli</i> BL21(DE3) carrying piGEM2018-Module001 was used to degrade straw to glucose. Three extracellular expressed enzymes ferulic acid esterase, xylanase and cellulase are involved in the pathway. The expression of the three target proteins were verified by enzyme activity using fermentation liquid and enzyme crude extract, respectively. The results showed that the activities of all three enzymes in fermentation liquid fraction are too low to be detected, which could be due to the fact of low enzyme concentration. We also determined the enzyme activity using enzyme crude extract. The enzyme activity in crude fraction obtained from the strain carrying piGEM2018-Module001 was higher than that without the corresponding vector for all enzymes.  
 
         </div>
 
         </div>
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        <div class="chatu" style="padding:20px 5%;"><img src="https://static.igem.org/mediawiki/2018/b/b5/T--UESTC-China--dem3.png" width="100%"></div>
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        <div class="tu">
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            Fig. 2 Enzyme activity detection using crude extract fraction of strain with or without. Module001:All sample were collected after fermentation for 24 h.
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<br>(a) The activity of xylanase. U/mL definition: 1 ml of enzyme solution (at 40 °C pH = 6.0) 1 h decomposition of xylan to produce 1 mg xylose, regarded as an enzyme unit [1];
 +
<br>(b) The activity of ferulic acid esterase. U/mL definition: The amount of enzyme (at 40 °C pH = 6.4) required to degrade 1 μmol of 4-nitrophenyl trans-ferulate per minute is one Unit of ferulic acid esterase activity [2];
 +
<br>(c) The activity of total cellulase. U/mL definition: 1 ml of enzyme solution (at 40 °C pH = 7.0) hydrolyzed the filter paper per minute to produce 1.0 μmol of glucose, which is one Unit of total cellulase activity [3];
 +
<br>(d) The activity of endoglucanase. U/mL definition: 1 ml of enzyme solution (at 40 ° C pH = 7.0) hydrolyzed CMC-Na per minute to produce 1.0 μmol of glucose, which is one Unit of endoglucanase activity [4].</div>
 
         <div class="zhengwen">
 
         <div class="zhengwen">
             Firstly, for quantitative assay, standard curves of ranging from 0-60mg/L Xylose were measured (Fig. 3). Then, we test the activity of xylan. Comparing with wild type, our E. coli carrying piGEM2018-Moudlu001 take effect. (Fig. 4)
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             In order to further evaluate the extracellular expression of ferulic acid esterase, xylanase and cellulose, the formation of the corresponding intermediates were determined. GC-MS was used to detect ferulic acid. We shaked <i>E. coli</i> BL21(DE3) carrying piGEM2018-Module001 with corn stalk and the ferulic acid production was monitored by periodically taking samples from the fermentation liquid of <i>E. coli</i> BL21(DE3) carrying piGEM2018-Module001. Carvacrol was used as an internal standard for GC measurements [5]. GC results showed that the peak of ferulic acid was appeared after fermentation for 24h with the strain carrying piGEM2018-Module001, while no ferulic acid was detected in the sample of <i>E. coli</i> BL21(DE3) without vector (Fig. 3). The ferulic acid peak was further analyzed by using GC-MS (Fig. 4).
 
         </div>
 
         </div>
         <div class="chatu" style="padding:20px 10%;"><img src="3" width="100%"></div>
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         <div class="chatu" style="padding:20px 20%;"><img src="https://static.igem.org/mediawiki/2018/2/2f/T--UESTC-China--dem4.png" width="100%"></div>
        <div class="tu">Figure 3.&nbsp; The standard curve of Xylose.</div>
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        <div class="chatu" style="padding:20px 10%;"><img src="4" width="100%"></div>
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        <div class="tu">Figure 4.&nbsp;Two groups of different sample solutions were added. Namely, Module001: </div>
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        <div class="tu">supernatant of piGEM-Module001. WT: supernatant of Wild Type. The strain BL21 (DE3) transformed with piGEM2018-Module001 was cultivated overnight and centrifuged to obtain the supernatant. The remaining bacteria were broken and broken products were obtained.1 ml xylan solution was added to 5 ml phosphate buffer solution (pH=6), incubated at 40 C for 5 min, and 1 ml sample solution was added. </div>
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        <div class="zhengwen">
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            Ferulic acid esterase can decompose ferulic acid p-nitrophenol ester to produce p-nitrophenol and ferulic acid. The changes of absorbance value under 410nm could be an indicator of changes in ferulic acid concentration. (Fig. 5)
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        </div>
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        <div class="chatu" style="padding:20px 10%;"><img src="5" width="100%"></div>
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        <div class="tu">Figure 5.&nbsp; The strain BL21 (DE3) transformed with piGEM2018-Module001 and wild type were broken. DSMO solution of ferulic acid p-nitrophenol ester was added to phosphate buffer solution of 630 L pH=6.4 with a concentration of 400 L of 10 mmol/L. Heat preservation 5min at 40℃ and add 0.2ml sample solution. The initial OD were same. Gently mix and incubate 4h at 40 C, determine the final OD value and compare the difference. </div>
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        <div class="zhengwen">
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            To fully determine that our plasmid has taken effect. We use GC-MS to detect ferulic acid. The ferulic acid production was monitored by periodically taking samples from the supernatant of E. coli carrying piGEM2018-Module001. GC-MS was used to detect the concentration of ferulic acid using the method reported in another paper [1]. Ferulic acid will undergo this reaction and decompose into 9 carbon compounds in the case of ferulic acid in gas chromatography with nitrogen as carrier gas (Fig. 6). Fig.7 is chromatograms of the supernatant samples, the peak of ferulic acid derivative was observed from samples of tobacco carrying piGEM2018-Module001 after 0h and 24h. Most importantly, the peak of ferulic acid derivative increased within 20 hours while ferulic acid derivative was not found in sample of wild-type E. coli. Fig.8 demonstrate that our product is ferulic acid by GC-MS.
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        </div>
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        <div class="chatu" style="padding:20px 10%;"><img src="6" width="100%"></div>
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         <div class="tu">
 
         <div class="tu">
             Figure 6.&nbsp;is chromatograms of the supernatant samples, the peak of ferulic acid derivative was observed from samples of tobacco carrying piGEM2018-Module001 after 0h and 24h. Most importantly, the peak of ferulic acid derivative increased within 20 hours while ferulic acid derivative was not found in sample of wild-type E. coli.
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             Fig. 3 The production of ferulic acid determined using GC. The supernatants of fermented liquid of <i>E. coli</i> BL21(DE3) with or without  piGEM2018-Module001were used for the determination of ferulic acid, respectively. Samples were shaking with corn straw and taken from reaction mixtureat 0h, 24h.
 
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         </div>
         <div class="chatu" style="padding:20px 10%;"><img src="7" width="100%"></div>
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         <div class="chatu" style="padding:20px 20%;"><img src="https://static.igem.org/mediawiki/2018/a/af/T--UESTC-China--dem5.png" width="100%"></div>
 
         <div class="tu">
 
         <div class="tu">
             Figure 7.&nbsp;Chromatogram of Ferulic Acid derivatives and Internal Standard carvarol in supernatant of transgenic E. coli carrying piGEM2018-Module001 and wild-type E. coli. Samples were taken from reaction mixture at 0h, 24h.
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             Fig. Mass spectrums of ferulic acid derivative. Sample was the supernatants of <i>E. coli</i> BL21(DE3) carrying piGEM2018-Module001 after fermentation for 24h.
        </div>
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        <div class="chatu" style="padding:20px 10%;"><img src="8" width="100%"></div>
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        <div class="tu">
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            Figure 8.&nbsp;Mass spectrums of ferulic acid derivative. Sample was transgenic E. coli carrying piGEM2018-Module001 and taken from reaction mixture at 24h.
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        </div>
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        <div class="zhengwen">
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            In order to find out if the cellulases had been expressed successfully in BL21 (DE3), the method of Congo Red assay was performed.
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        </div>
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        <div class="zhengwen">
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            Cellulases can cut CMC-Na into short chains. As Congo Red only binds to long chain polysaccharides CMC-Na but not short chain resulting in halo formation.
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             The results are shown in Fig.9. The strains carrying piGEM2018-Module001 showed a zone of clearance created by hydrolysis of CMC showed that cellulases was successfully transcribed and translated by BL21(DE3). The empty vector control didn't show any zone of clearance around the colonies.
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             The activity of cellulase was determined by using Congo Red assay [6].  As shown in Fig. 5, the strains carrying piGEM2018-Module001 displayed a zone of clearance. Such a zone of clearance was also observed in the positive control carried out by using commercial cellulase, while no zone of clearance was observed with same <i>E. coli</i> strain carrying empty vector. The results indicated that cellulase was successfully extracellularly expressed in <i>E. coli</i> BL21(DE3) with piGEM2018-Module001.  
 
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         <div class="chatu" style="padding:20px 10%;"><img src="9" width="100%"></div>
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         <div class="chatu" style="padding:20px 10%;"><img src="https://static.igem.org/mediawiki/2018/c/c7/T--UESTC-China--dem6.png" width="100%"></div>
 
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             Figure 9.&nbsp;Line 1: BL21(DE3) carrying piGEM2018-Module001 (OD600=1, 3, 5 from left to right) Line 2: Positive control enzyme (concentration=0.2, 0.3, 0.4 mg/ml from left to right) Line 3: BL21(DE3) carrying empty vector control (OD600=1, 3, 5 from left to right)
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             Fig. 5  Activity determination of cellulase using Congo Red assay. (a) CMC agar plate before staining with Congo Red. (b)CMC agar plate after staining with Congo Red. Module001: BL21(DE3) carrying piGEM2018-Module001(OD600: 1, 3, 5 from left to right); Positive Control: commercial cellulase (Enzyme concentration: 0.2, 0.3, 0.4 mg/ml from left to right); Negative Control: BL21 (DE3) carrying empty vector (OD600: 1, 3, 5 from left to right)
 
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            To further detect the function of cellulases, we tested cellulases and cenA activity. Providing data for previously submitted parts ( BBa_K118022, BBa_K118022). Firstly, for quantitative assay, standard curves of ranging from 0-1000mg/L glucose were measured (Fig.10).
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             Figure 10.&nbsp;The standard curve of Glucose.
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             3. Butanol production
 
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             We measured the release of reducing sugar from filter paper by the 3,5-dinitrosalicylic acid (DNS) method for the cellulases activity.
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             <i>E. coli</i> BL21(DE3) carrying piGEM2018-Module002 was used to convert  glucose to butanol. Five enzymes AtoB, Hbd, Crt, Ter and AdhE2 are involved in the pathway, which was validated by monitoring the production of butanol using GC. To test whether this multi-enzyme conversion system could work in our <i>E. coli</i> successfully or not, we detected the production curve of butanol.
 
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             The total amount of reducing sugars was expressed as glucose equivalents according to a standard curve prepared with glucose in the range from 0 to 1000 mg/L−1.
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             The butanol production was determined by periodically taking samples from the supernatant of fermented liquid of BL21(DE3). Isobutanol was used as an internal standard [7]. The results showed that the peak of butanol was appeared after fermentation for 24h with the strain carrying piGEM2018-Module002, while no butanol peak was observed for the negative control <i>E. coli</i> BL23(DE3) with empty vector(Fig. 6).
 
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         <div class="chatu" style="padding:20px 10%;"><img src="11" width="100%"></div>
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         <div class="chatu" style="padding:20px 20%;"><img src="https://static.igem.org/mediawiki/2018/2/21/T--UESTC-China--dem7.png" width="100%"></div>
 
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             Figure 11.&nbsp;Reactions were carried out in 50 ml centrifuge tubes with 50 mg of filter paper (1 cm × 6 cm piece) in 1.0 ml potassium phosphate buffer (50mM, pH 7.0), plus 0.5 ml of the crude enzyme solution. Reaction mixtures were incubated at 40 °C for 3 h, enzyme action was interrupted by the addition of 3,5-dinitrosalisylic acid (DNS) reagent, which was used to quantify the total amount of reducing sugars. Reaction mixtures were then placed in a boiling water bath for 5 min, cooled to room temperature and diluted to 25 ml with water for the measurement of absorbance at 540 nm with a spectrophotometer.
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             Fig. 6  The production of butanol determined using GC. The supernatants of fermented liquid of <i>E. coli</i> BL21(DE3) with or without piGEM2018-Module002 were used for the determination of butanol, respectively. For anaerobic growth, precultures were adjusted to OD600 10 with 2 mL of fresh medium with 50mg/mL kanamycin. The culture was transferred to a sealed 10ml vacuum tube. Cultures were shaken (200 rpm) at 37 °C for 24 h. Then samples were taken from reaction mixture at 0h, 24h.
 
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             In addition, we measured the release of reducing sugar from CMC-Na with the 3,5-dinitrosalicylic acid (DNS) method for cenA activity. As shown in Fig 12, BL21(DE3) carrying piGEM2018-Module001 could Bacteria decompose CMC-Na while wild-type couldn't, which proved that cenA could work successfully.
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             To improve butanol production, the fermentation conditions were optimized by using orthogonal array design by designing 17 three factor analysis. After a serious of butanol-production detection under different cultivating condition, we finally provided the necessary data for modeling. Then detecting the butanol production in 24h under the optimized conditions. (Fig. 7) And the final maximum yield of butanol is 0.406 g / L in 26 hours.
 
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         <div class="chatu" style="padding:20px 10%;"><img src="12" width="100%"></div>
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         <div class="chatu" style="padding:20px 10%;"><img src="https://static.igem.org/mediawiki/2018/1/10/T--UESTC-China--butanolture.png" width="100%"></div>
 
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             Figure 12.&nbsp;The concentration of reducing sugar after 3 hours. Reaction proceeded in 50 mM potassium phosphate buffer (pH = 7.0) at 40°C. Module001: The crude enzyme solution obtained by ultrasonication of BL21(DE3) carrying is involved in the reaction. Wild Type: The crude enzyme solution obtained by ultrasonication of wild-type BL21(DE3) participated in the reaction. CMC-Na:The same amount of CMC-Na participated in the reaction as a control. Each data represents the mean value ± standard deviation from two independent experiments.
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             Fig. The butanol production curve at optimized conditions (temperature=34℃, initial OD=13, initial pH=8)
 
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             Butanol production
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             4. Hydrogen production
 
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             Work validation of multi-enzyme system in BL21(DE3) carrying piGEM2018-Module002. AtoB,Hbd,crt,ter and adhE2 catalyzed six-step reactions converting glucose to butanol. To test whether this multi-enzyme conversion system could work in our E. coli successfully or not, we detected the time production curve of butanol of BL21(DE3) carrying piGEM2018-Module002 under the anaerobic condition. Significantly, the peak of butanol increased within 24 hours while it was not found in sample of wild-type BL23(DE3).(Fig.13)
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             To verify whether the piGEM2018-Module003 plasmid was working normally in <i>E. coli</i> DH5α, we set up an anaerobic fermentation unit. The produced gases flow through the following setup to remove carbon dioxide as much as possible to get hydrogen.
 
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         <div class="chatu" style="padding:20px 10%;"><img src="13" width="100%"></div>
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             Figure 13.&nbsp;Chromatogram of butanol and Internal iosbutanol of transgenic E. coli carrying piGEM2018-Module002 and wild-type E. coli. Samples were taken from reaction mixture at 0h, 24h.
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             Fig. 8 Overall setup of the hydrogen collection device.
 
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             For quantitative assay, standard curves of butanol ranging from 1-5g/L were measured (Fig. 14). The butanol production was monitored using the method of gas chromatography by periodically taking samples from the supernatant of fermented liquid, and the internal standard is isobutanol. [2]
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             The collected gas is qualitatively detected by combustion test. As seen from Video 1, one can clearly hear the sound of boom, while no similar phenomenon was observed for the control group.
 
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            Figure 14.&nbsp;Standard curve of Butanol.
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                <a href="https://static.igem.org/mediawiki/2018/d/d9/T--UESTC-China--H2_%281%29.mp4">Download Video</a>
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            Furthermore, after a serious of butanol-production detection under different cultivating condition, we finally provided the necessary data for modeling. And detecting the butanol production in 48h under the optimized conditions. And the final maximum yield of butanol is 0.37 g / L.
 
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             Figure 15.&nbsp; The butanol production curve at optimized conditions (temperature=34℃, initial OD=13, Initial pH=8)
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             Video 1. The video of gas combustion test. Samples were collected from the engineered <i>E. coli</i> DH5α carrying the plasmid piGEM2018-Module003 and wild type plasmid after shaking 48h in TB medium.
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            Hydrogen production
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            First, in order to verify that the gene expressed the protein in E. coli, we performed SDS-PAGE on the DH5α bacterial solution containing piGEM-Module003 and the control bacterial solution. FhlA has a brighter band at 97.4 kDa and Hyda has a brighter band at 42 kDa.
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Next, we used gas collection devices to quantitatively detect hydrogen production. The recombinant strain and the original DH5α strain were fermented continuously for 36 hours in a 200 ml 1% (W/V) glucose M9 medium. Fig. 9 illustrates that our <i>E. coli</i> DH5α with piGEM2018-Module003 has higher hydrogen production than the original strain. At the same time, the hydrogen production of the recombinant bacteria increased exponentially with time (0-36h). Up to the end of fermentation, the yield of recombinant bacteria was 2.17mL/hr, which was 2.4 times higher than that of the original strain.
 
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         <div class="chatu" style="padding:20px 10%;"><img src="16" width="100%"></div>
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         <div class="chatu" style="padding:20px 10%;"><img src="https://static.igem.org/mediawiki/2018/4/43/T--UESTC-China--dem10.png" width="100%"></div>
 
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             Figure 16.&nbsp; M: Marker, WT: wild type, Module 003: piGEM2018-003 in DH5α. All samples were obtained after breaking the cultivating E.coli DH5α for 4h at 37℃, 180rpm.
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             Fig. 9  A diagram of the volume of hydrogen generated over time in a gas collection device. Recombinant strain and original strain were fermented in 200 ml 1% (W/V) glucose M9 medium.
 
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             Next, it was verified whether the piGEM-Module003 plasmid was working normally in Escherichia coli DH5α. We set up an anaerobic fermentation unit. Because E. coli produces only carbon dioxide and hydrogen under anaerobic conditions, the removal of carbon dioxide theoretically allows us to produce relatively pure hydrogen.
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             Apart from the experiments, here we also carried out some theoretical modeling to provide some guidance to optimize the experimental condition. As demonstrated as following, 1 mol glucose can produce 2 mol hydrogen from the theoretical point of view [8]. In order to explore the optimal conditions for hydrogen production from <i>E. coli</i> DH5α with piGEM2018-Module003 more efficiently, we used vacuum vascularization (10mL) with 1mL 1% (w/v) glucose M9 medium and 100 microliters of recombinant bacteria growing to logarithmic metaphase to ferment under different conditions. Next, we measured the amount of hydrogen and formation rate following the 40hr anaerobic fermentation. The results showed that under the condition of 30°C, 1.13% (W/V), pH=6.8, our recombinant strain has the highest hydrogen production. Based on this, we compare our hydrogen production with relevant literatures. The results are as follows (Fig. 10).
 
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         <div class="chatu" style="padding:20px 10%;"><img src="17" width="100%"></div>
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         <div class="chatu" style="padding:20px 10%;"><img src="https://static.igem.org/mediawiki/2018/e/e9/T--UESTC-China--dem--10.png" width="100%"></div>
 
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             Figure 17.&nbsp; The left side of the apparatus is a carbon dioxide generating apparatus, and carbon dioxide is produced by dropping a dilute hydrochloric acid into a flask containing CaCO3 under the separatory funnel. The middle part of the device is a bacterial liquid fermentation device consisting of a three-necked flask placed on a temperature-controlled magnetic stirrer. The magnetic stirrer can continuously stir the bacteria liquid and keep the temperature constant. The right side of the unit consists of two scrubbers and a sink. The first scrubber bottle is filled with a sodium hydroxide solution to remove carbon dioxide and hydrogen chloride gas from the mixed gas. In the second scrubber is a clarified lime water used to verify that the carbon dioxide gas has been removed. The final product gas is then collected using a drainage gas collection method in the water tank.
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             Fig. 10 Comparing our hydrogen production with relevant literatures.
 
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            Firstly, for quantitative assay, standard curves of ranging from 0-9ml hydrogen were measured (Fig. 17). Then, we measure hydrogen using gas chromatography. Fig.XX is chromatograms of the gas samples, the peak of hydrogen was observed from samples of DH5α carrying piGEM2018-Module003 after 0h and 24h. Most importantly, the peak of butanol increased within 24 hours while it was not found in sample of wild-type BL23(DE3).
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Fig. 10 shows that our <i>E. coli</i> DH5α with piGEM2018-Module003 hydrogen production is higher than most of the knockout and overexpression methods for <i>E. coli</i>'s own genes, but there is still a gap compared with the methods for cloning some heterologous genes into <i>E. coli</i>.  
 
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             Figure 18.&nbsp; Standard curve of Hydrogen.
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         <div class="bigtitle">
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            5. Work going on
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        </div>
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             Import suicide gene
 
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            We use gas chromatography (GC) to verify the gas produced by the fermentation unit. We injected three different gases, 5% hydrogen with 95% carbon dioxide, the gas produced by the DH5α fermentation of the piGEM-Module003 plasmid, and the gas after fermentation of the original DH5α strain. Fig
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The risks of our project are about the antibiotic resistance genes in case of the accident of incorrectly operation. However, it’s not uncontrollable. We plan to add a “suicide gene” leading the bacteria to express endolysin to kill themselves when they escape our cultivate medium.</div>      
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         <div class="smtitle">
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             Import resistance gene
             Figure 19.&nbsp;
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         <div class="zhengwen">
             The theoretical maximum yield of facultative anaerobic bacteria is 2 moles H2 per mole of glucose. Based on the optimum reaction conditions for the modeling guidelines, we tested the hydrogen content and rate of production in the 40-hour anaerobic fermentation gas. The end result is x moles of hydrogen per gram of glucose.
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             GroESL, which is a combination of GroEL and GroES gene has been shown to increase butanol production in <i>E. coli</i> [12]. We have test the tolerance of <i>E. coli</i> BW25113 with GroESL gene and original BW25113 under the condition of 1% (v/V) butanol concentration. The result shows that GroESL has a positive effect on the butanol tolerance of <i>E. coli</i> (Fig. 11). In the future, we will use <i>E. coli</i> BW25113 combining piGEM2018-Module002 with GroESL gene to produce butanol.  
 
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         <div class="chatu" style="padding:20px 10%;"><img src="20" width="100%"></div>
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         <div class="chatu" style="padding:20px 10%;"><img src="https://static.igem.org/mediawiki/2018/1/1c/T--UESTC-China--dem12.png" width="100%"></div>
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         <div class="tu">Fig. 11  After adding 0.3ml butanol in 30ml LB medium, the measurement of optical density (OD600) deference between DH5α with GroESL and Negative Control in 24 hour.</div>
             Figure 20.&nbsp;
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        <div class="smtitle">
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             Knock out relevant gene
 
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             Now, let’s listen to the beautiful sound.
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             Due to limitations of experimental conditions, we are not able to knock out competitive pathway. However, many by-products will produce in the process of butanol production, namely frdABCD for succinate, ldhA for lactate, pta-ack for acetate, and adhE for ethanol (Fig. 12)[13]. If we could knock out these competitive pathway, then our butanol production will be greatly improved.
 
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         video
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         <div class="chatu" style="padding:20px 25%;"><img src="https://static.igem.org/mediawiki/2018/a/aa/T--UESTC-China--dem13.png" width="100%"></div>
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        <div class="tu">Fig. 12  <i>E. coli</i> self-metabolic pathway</div>
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             Work going on
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             7. References
 
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             During the production process, the accumulation of butanol will exert a great inhibitory effect on cell growth. Therefore, we will introduce the GroEL gene and GroES gene from clostridium acetone butanol to make Escherichia coli heterologous expression of heat shock protein -- a molecular chaperone of GroESL, which has been shown to increase butanol production. Fig. 18 shows that GroESL have a good effect on butanol tolerance.
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             <div>[1]Shen C, Li R, Hu T & Yan K. 2011. Determination of xylanase activity with DNS method. Dyeing & Finishing, 2: 35-39.</div>
        </div>
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            <div>[2]Zhang S, Pei X & Wu Z. 2009. Cloning and expression of feruloyl esterase A from Aspergillus niger, and establishment of fast activity detection methods. Chinese Journal of Applied & Environmental Biology, 2: 276-279.</div>
        <div class="chatu" style="padding:20px 10%;"><img src="21" width="100%"></div>
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            <div>[3]Luciano Silveira MH, Rau M, Pinto da Silva Bon E & Andreaus J. 2012. A simple and fast method for the determination of endo- and exo-cellulase activity in cellulase preparations using filter paper. Enzyme and Microbial Technology, 51: 280-285.
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             Figure 21.&nbsp; After adding 0.3ml butanol in 30ml LB medium, the measurement of optical density (A600) deference between DH5α with GroESL and Negative Control in 24 hour.
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            <div>[4]Wood TM & Bhat KM. 1988. Methods for measuring cellulase activities. Methods in Enzymology, 160: 87-112.
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</div>
 +
            <div>[5]Li Q, Gan G, Wang G & Liu Y. 2007. Determination of ferulic acid in ligusticum chuanxiong Hort.Oil by GC. Lishizhen Medicine & Materia Medica Research, 7: 1687-1688.
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</div>
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            <div>[6]Lakhundi SS. Synthetic biology approach to cellulose degradation[D]. Edinburgh: University of Edinburgh, 2012.
 +
</div>
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            <div>[7]Atsumi S, Cann AF, Connor MR, Shen CR, Smith KM, Brynildsen MP & Liao JC. 2008. Metabolic engineering of E. coli for 1-butanol production. Metabolic Engineering, 10: 305-311.
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</div>
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            <div>[8]Hallenbeck PC & Ghosh D. 2012. Improvements in fermentative biological hydrogen production through metabolic engineering. Journal of Environmental Management, 95: 360-364.</div>
 +
            <div>[9]Yoshida A, Nishimura T, Kawaguchi H, Inui M & Yukawa H. 2006. Enhanced hydrogen production from glucose using ldh- and frd-inactivated Escherichia coli strains. Applied Microbiology and Biotechnology, 73: 67-72.</div>
 +
            <div>[10]Akhtar MK & Jones PR. 2009. Construction of a synthetic YdbK-dependent pyruvate:H2 pathway in Escherichia coli BL21(DE3). Metabolic Engineering, 11: 139-147.</div>
 +
             <div>[11]Chittibabu G, Nath K & Das D. 2006. Feasibility studies on the fermentative hydrogen production by recombinant escherichia coli, bl-21. Process Biochemistry, 41: 682-688.
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</div>
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            <div>[12]Abdelaal AS, Ageez AM, El AEHAA & Abdallah NA. 2015. Genetic improvement of n-butanol tolerance in Escherichia coli by heterologous overexpression of groESL operon from Clostridium acetobutylicum. 3 Biotech, 5: 401-410.</div>
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            <div>[13]Shen C & Liao J. 2008. Metabolic engineering of Escherichia coli for 1-butanol and 1-propanol production via the keto-acid pathways. Metabolic Engineering, 10: 312-320.</div>
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            Reference
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        <div class="zhengwen">[6]Fiddler, W., Parker, W. E., Wasserman, A. E., & Doerr, R. C. (1967). Thermal decomposition of ferulic acid. Journal of Agricultural and Food Chemistry, 15(5), 757-761.</div>
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        <div class="zhengwen">[7] Atsumi, S., Cann, A. F., Connor, M. R., Shen, C. R., Smith, K. M., Brynildsen, M. P., ... & Liao, J. C. (2008). Metabolic engineering of Escherichia coli for 1-butanol production. Metabolic engineering, 10(6), 305-311.</div>
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Latest revision as of 03:25, 18 October 2018

team

  • 1. Pathway construction
    For efficient expression of multiple enzymes in E. coli, codon optimization of all target genes were performed before DNA synthesis. The obtained genes were subsequently cloned into different expression vectors by using Gibson Assembly and Golden Gate strategies. The resulting vectors piGEM2018-Module001, piGEM2018-Module002, and piGEM2018-Module003 are listed in Table 1.
    Table 1   Illustration of the three constructed vectors.
    No. Vector E. coli resistance Description
    1 piGEM2018-Module001 Amp BBa_J23100-RBS-pelB+5D-Xyn10D-Fae1A-RBS-pelB+5D-Xyl3A-RBS-pelB+5D-Cex-RBS-pelB+5D-CenA-Ter
    2 piGEM2018-Module002 Kan Ter-Ter-RBS-Fdh-RBS-FRE_adhE-FRE_ackA-RBS-AtoB-RBS-AdhE2-RBS-Crt-RBS-Hbd-Ter
    3 piGEM2018-Module003 Kan BBa_J23100-RBS-FhlA-RBS-HydA-Ter
    Before DNA sequencing, those vectors were verified by restriction enzyme digestion. After electrophoresis analysis, the samples which contained the desired bands were selected and sent for sequencing. The sequencing results showed that all the above constructed vectors were successful. (Fig. 1)
    Fig. 1 Double restriction enzyme digestion of three constructed vectors analyzed by using agarose gel electrophoresis.
    (a) piGEM2018-Module001 digested by Eco32Ⅰ+NcoⅠ(lane 1), piGEM2018-Module001 digested by NcoⅠ+XhoⅠ(lane 2);
    (b) piGEM2018-Module002 digested by PstⅠ+KpnⅠ(lane 1), piGEM2018-Module002 digested by HindⅢ+KpnⅠ(lane 2);
    (c) piGEM2018-Module003 digested by EcoRⅠ+NcoⅠ(lane 1), piGEM2018-Module003 digested by BamHⅠ+BglⅡ(lane 2).
  • 2. From straw to glucose
    E. coli BL21(DE3) carrying piGEM2018-Module001 was used to degrade straw to glucose. Three extracellular expressed enzymes ferulic acid esterase, xylanase and cellulase are involved in the pathway. The expression of the three target proteins were verified by enzyme activity using fermentation liquid and enzyme crude extract, respectively. The results showed that the activities of all three enzymes in fermentation liquid fraction are too low to be detected, which could be due to the fact of low enzyme concentration. We also determined the enzyme activity using enzyme crude extract. The enzyme activity in crude fraction obtained from the strain carrying piGEM2018-Module001 was higher than that without the corresponding vector for all enzymes.
    Fig. 2 Enzyme activity detection using crude extract fraction of strain with or without. Module001:All sample were collected after fermentation for 24 h.
    (a) The activity of xylanase. U/mL definition: 1 ml of enzyme solution (at 40 °C pH = 6.0) 1 h decomposition of xylan to produce 1 mg xylose, regarded as an enzyme unit [1];
    (b) The activity of ferulic acid esterase. U/mL definition: The amount of enzyme (at 40 °C pH = 6.4) required to degrade 1 μmol of 4-nitrophenyl trans-ferulate per minute is one Unit of ferulic acid esterase activity [2];
    (c) The activity of total cellulase. U/mL definition: 1 ml of enzyme solution (at 40 °C pH = 7.0) hydrolyzed the filter paper per minute to produce 1.0 μmol of glucose, which is one Unit of total cellulase activity [3];
    (d) The activity of endoglucanase. U/mL definition: 1 ml of enzyme solution (at 40 ° C pH = 7.0) hydrolyzed CMC-Na per minute to produce 1.0 μmol of glucose, which is one Unit of endoglucanase activity [4].
    In order to further evaluate the extracellular expression of ferulic acid esterase, xylanase and cellulose, the formation of the corresponding intermediates were determined. GC-MS was used to detect ferulic acid. We shaked E. coli BL21(DE3) carrying piGEM2018-Module001 with corn stalk and the ferulic acid production was monitored by periodically taking samples from the fermentation liquid of E. coli BL21(DE3) carrying piGEM2018-Module001. Carvacrol was used as an internal standard for GC measurements [5]. GC results showed that the peak of ferulic acid was appeared after fermentation for 24h with the strain carrying piGEM2018-Module001, while no ferulic acid was detected in the sample of E. coli BL21(DE3) without vector (Fig. 3). The ferulic acid peak was further analyzed by using GC-MS (Fig. 4).
    Fig. 3 The production of ferulic acid determined using GC. The supernatants of fermented liquid of E. coli BL21(DE3) with or without piGEM2018-Module001were used for the determination of ferulic acid, respectively. Samples were shaking with corn straw and taken from reaction mixtureat 0h, 24h.
    Fig. 4 Mass spectrums of ferulic acid derivative. Sample was the supernatants of E. coli BL21(DE3) carrying piGEM2018-Module001 after fermentation for 24h.
    The activity of cellulase was determined by using Congo Red assay [6]. As shown in Fig. 5, the strains carrying piGEM2018-Module001 displayed a zone of clearance. Such a zone of clearance was also observed in the positive control carried out by using commercial cellulase, while no zone of clearance was observed with same E. coli strain carrying empty vector. The results indicated that cellulase was successfully extracellularly expressed in E. coli BL21(DE3) with piGEM2018-Module001.
    Fig. 5 Activity determination of cellulase using Congo Red assay. (a) CMC agar plate before staining with Congo Red. (b)CMC agar plate after staining with Congo Red. Module001: BL21(DE3) carrying piGEM2018-Module001(OD600: 1, 3, 5 from left to right); Positive Control: commercial cellulase (Enzyme concentration: 0.2, 0.3, 0.4 mg/ml from left to right); Negative Control: BL21 (DE3) carrying empty vector (OD600: 1, 3, 5 from left to right)
  • 3. Butanol production
    E. coli BL21(DE3) carrying piGEM2018-Module002 was used to convert glucose to butanol. Five enzymes AtoB, Hbd, Crt, Ter and AdhE2 are involved in the pathway, which was validated by monitoring the production of butanol using GC. To test whether this multi-enzyme conversion system could work in our E. coli successfully or not, we detected the production curve of butanol.
    The butanol production was determined by periodically taking samples from the supernatant of fermented liquid of BL21(DE3). Isobutanol was used as an internal standard [7]. The results showed that the peak of butanol was appeared after fermentation for 24h with the strain carrying piGEM2018-Module002, while no butanol peak was observed for the negative control E. coli BL23(DE3) with empty vector(Fig. 6).
    Fig. 6 The production of butanol determined using GC. The supernatants of fermented liquid of E. coli BL21(DE3) with or without piGEM2018-Module002 were used for the determination of butanol, respectively. For anaerobic growth, precultures were adjusted to OD600 10 with 2 mL of fresh medium with 50mg/mL kanamycin. The culture was transferred to a sealed 10ml vacuum tube. Cultures were shaken (200 rpm) at 37 °C for 24 h. Then samples were taken from reaction mixture at 0h, 24h.
    To improve butanol production, the fermentation conditions were optimized by using orthogonal array design by designing 17 three factor analysis. After a serious of butanol-production detection under different cultivating condition, we finally provided the necessary data for modeling. Then detecting the butanol production in 24h under the optimized conditions. (Fig. 7) And the final maximum yield of butanol is 0.406 g / L in 26 hours.
    Fig. 7 The butanol production curve at optimized conditions (temperature=34℃, initial OD=13, initial pH=8)
  • 4. Hydrogen production
    To verify whether the piGEM2018-Module003 plasmid was working normally in E. coli DH5α, we set up an anaerobic fermentation unit. The produced gases flow through the following setup to remove carbon dioxide as much as possible to get hydrogen.
    Fig. 8 Overall setup of the hydrogen collection device.
    The collected gas is qualitatively detected by combustion test. As seen from Video 1, one can clearly hear the sound of boom, while no similar phenomenon was observed for the control group.
    Video 1. The video of gas combustion test. Samples were collected from the engineered E. coli DH5α carrying the plasmid piGEM2018-Module003 and wild type plasmid after shaking 48h in TB medium.
    Next, we used gas collection devices to quantitatively detect hydrogen production. The recombinant strain and the original DH5α strain were fermented continuously for 36 hours in a 200 ml 1% (W/V) glucose M9 medium. Fig. 9 illustrates that our E. coli DH5α with piGEM2018-Module003 has higher hydrogen production than the original strain. At the same time, the hydrogen production of the recombinant bacteria increased exponentially with time (0-36h). Up to the end of fermentation, the yield of recombinant bacteria was 2.17mL/hr, which was 2.4 times higher than that of the original strain.
    Fig. 9 A diagram of the volume of hydrogen generated over time in a gas collection device. Recombinant strain and original strain were fermented in 200 ml 1% (W/V) glucose M9 medium.
    Apart from the experiments, here we also carried out some theoretical modeling to provide some guidance to optimize the experimental condition. As demonstrated as following, 1 mol glucose can produce 2 mol hydrogen from the theoretical point of view [8]. In order to explore the optimal conditions for hydrogen production from E. coli DH5α with piGEM2018-Module003 more efficiently, we used vacuum vascularization (10mL) with 1mL 1% (w/v) glucose M9 medium and 100 microliters of recombinant bacteria growing to logarithmic metaphase to ferment under different conditions. Next, we measured the amount of hydrogen and formation rate following the 40hr anaerobic fermentation. The results showed that under the condition of 30°C, 1.13% (W/V), pH=6.8, our recombinant strain has the highest hydrogen production. Based on this, we compare our hydrogen production with relevant literatures. The results are as follows (Fig. 10).
    Fig. 10 Comparing our hydrogen production with relevant literatures.
    Fig. 10 shows that our E. coli DH5α with piGEM2018-Module003 hydrogen production is higher than most of the knockout and overexpression methods for E. coli's own genes, but there is still a gap compared with the methods for cloning some heterologous genes into E. coli.
  • 5. Work going on
    Import suicide gene
    The risks of our project are about the antibiotic resistance genes in case of the accident of incorrectly operation. However, it’s not uncontrollable. We plan to add a “suicide gene” leading the bacteria to express endolysin to kill themselves when they escape our cultivate medium.
    Import resistance gene
    GroESL, which is a combination of GroEL and GroES gene has been shown to increase butanol production in E. coli [12]. We have test the tolerance of E. coli BW25113 with GroESL gene and original BW25113 under the condition of 1% (v/V) butanol concentration. The result shows that GroESL has a positive effect on the butanol tolerance of E. coli (Fig. 11). In the future, we will use E. coli BW25113 combining piGEM2018-Module002 with GroESL gene to produce butanol.
    Fig. 11 After adding 0.3ml butanol in 30ml LB medium, the measurement of optical density (OD600) deference between DH5α with GroESL and Negative Control in 24 hour.
    Knock out relevant gene
    Due to limitations of experimental conditions, we are not able to knock out competitive pathway. However, many by-products will produce in the process of butanol production, namely frdABCD for succinate, ldhA for lactate, pta-ack for acetate, and adhE for ethanol (Fig. 12)[13]. If we could knock out these competitive pathway, then our butanol production will be greatly improved.
    Fig. 12 E. coli self-metabolic pathway
  • 7. References
    [1]Shen C, Li R, Hu T & Yan K. 2011. Determination of xylanase activity with DNS method. Dyeing & Finishing, 2: 35-39.
    [2]Zhang S, Pei X & Wu Z. 2009. Cloning and expression of feruloyl esterase A from Aspergillus niger, and establishment of fast activity detection methods. Chinese Journal of Applied & Environmental Biology, 2: 276-279.
    [3]Luciano Silveira MH, Rau M, Pinto da Silva Bon E & Andreaus J. 2012. A simple and fast method for the determination of endo- and exo-cellulase activity in cellulase preparations using filter paper. Enzyme and Microbial Technology, 51: 280-285.
    [4]Wood TM & Bhat KM. 1988. Methods for measuring cellulase activities. Methods in Enzymology, 160: 87-112.
    [5]Li Q, Gan G, Wang G & Liu Y. 2007. Determination of ferulic acid in ligusticum chuanxiong Hort.Oil by GC. Lishizhen Medicine & Materia Medica Research, 7: 1687-1688.
    [6]Lakhundi SS. Synthetic biology approach to cellulose degradation[D]. Edinburgh: University of Edinburgh, 2012.
    [7]Atsumi S, Cann AF, Connor MR, Shen CR, Smith KM, Brynildsen MP & Liao JC. 2008. Metabolic engineering of E. coli for 1-butanol production. Metabolic Engineering, 10: 305-311.
    [8]Hallenbeck PC & Ghosh D. 2012. Improvements in fermentative biological hydrogen production through metabolic engineering. Journal of Environmental Management, 95: 360-364.
    [9]Yoshida A, Nishimura T, Kawaguchi H, Inui M & Yukawa H. 2006. Enhanced hydrogen production from glucose using ldh- and frd-inactivated Escherichia coli strains. Applied Microbiology and Biotechnology, 73: 67-72.
    [10]Akhtar MK & Jones PR. 2009. Construction of a synthetic YdbK-dependent pyruvate:H2 pathway in Escherichia coli BL21(DE3). Metabolic Engineering, 11: 139-147.
    [11]Chittibabu G, Nath K & Das D. 2006. Feasibility studies on the fermentative hydrogen production by recombinant escherichia coli, bl-21. Process Biochemistry, 41: 682-688.
    [12]Abdelaal AS, Ageez AM, El AEHAA & Abdallah NA. 2015. Genetic improvement of n-butanol tolerance in Escherichia coli by heterologous overexpression of groESL operon from Clostridium acetobutylicum. 3 Biotech, 5: 401-410.
    [13]Shen C & Liao J. 2008. Metabolic engineering of Escherichia coli for 1-butanol and 1-propanol production via the keto-acid pathways. Metabolic Engineering, 10: 312-320.
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