Team:Hong Kong HKUST/InterLab

iGem HKUST 2018 Hielo by TEMPLATED
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INTERLAB

OUR INTERLAB OBJECTIVES

The 2018 year iGEM interlab aimed at reducing Lab-to-lab variability in fluorescence measurement as previous interlab studies have shown the variation in using optical density (O.D.) to measure level of GFP expression per cell. It was hypothesized that the large variability in fluorescence measurement is due to the O.D. being an approximation of cell number. To address this issue, this year’s interlab studies will focus on two approaches, the use of absolute cell count and colony forming units (CPU), to replace the use of O.D. measurements.

Method:

All procedures were performed according to the protocols given by iGEM. However, the OD measurement was changed from OD600 to OD595, due to the limited options of plate reader available in HKUST. With approval from the iGEM headquarter, we retained using the OD595 data. Summary of material used and data we have collected will be described below.

Machines, materials and parts:

    Machines:


  • Envision Multilabel Reader

*To know more about the setting of EnVision multilabel reader, please click

  • LUDOX CL-X,/b>: 45% colloidal silica suspension, use as single reference point for converting absorbance (Abs600) to OD600
    .
  • Silica beads: Microsphere suspension that mimic the shape and size of typical E.coli cell. With known concentration, it is used as conversion of absorbance measurement to universal standard concentration of bead measurement.

  • Fluorescein: fluorescent molecules for create standard fluorescence curve.

  • E.coli strain DH5αCompetent cell: use for transformation, the protocol used for making it can view in here

parts:

Parts Parts location on the kits plate Parts used as the promoter(strength) Parts used as the RBS(Efficiency) Reporter Gene Parts used as the Terminator
Positive Control(BBa_I20270) Plate 7 Well 2B BBa_J23151 (nil) BBa_B0032 (0.3) GFP BBa_B0010, BBa_B0012
Negative Control (BBa_R0040) Plate 7 Well 2D BBa_R0040 (nil) nil
Test Device 1 (BBa_J364000) Plate 7 Well 2F BBa_J23101 (1791au) BBa_B0034 (1.0)
Test Device 2 (BBa_J364001) Plate 7 Well 2H BBa_J23106 (1185au)
Test Device 3 (BBa_J364002) Plate 7 Well 2J BBa_J23117 (162au)
Test Device 4 (BBa_J364007) Plate 7 Well 2L BBa_J23100(2547au) BBa_B0034* (nil)
Test Device 4 (BBa_J364007) Plate 7 Well 2L BBa_J23100(2547au) BBa_B0034* (nil)

Result:

Calibrations:

Conversion factor of OD600(OD600/Abs600) = 3.036
LUDOX CL-X H20
Replicate 1 0.045 0.024
Replicate 2 0.045 0.025
Replicate 3 0.044 0.024
Replicate 4 0.049 0.027
Arithmethic mean 0.046 0.025
Corrected Abs600 0.021
Reference OD600 0.063
OD600/Abs600 3.036
Table2: Conversion factor calculation

Responsive image
Fig. 2a Particle Standard Curve
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Fig.2b Particle Standard Curve (log scale)
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Fig.3a Fluorescein standard curve
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Fig.3a Fluorescein standard curve (log scale)

Converting between absorbance of cells to absorbance of a known concentration of beads.

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Fig.4 Average uM Fluorescein / OD600 of each devices
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Fig.3a Fluorescein standard curve (log scale)

Counting colony-forming units (CFUs) from the sample


Colonies count:
Negative control (BBa_R0040):

Dillution 3 Dillution 4 Dillution 5
Colony 1, Replicate 1 180 13 3
Colony 1, Replicate 2 120 14 3
Colony 1, Replicate 3 197 33 2
Colony 2, Replicate 1 283 33 2
Colony 2, Replicate 2 214 28 3
Colony 2, Replicate 3 218 29 1
Positive control ((BBa_I120270):
Dillution 3 Dillution 4 Dillution 5
Colony 1, Replicate 1 228 29 1
Colony 1, Replicate 2 184 25 1
Colony 1, Replicate 3 153 25 1
Colony 2, Replicate 1 254 19 3
Colony 2, Replicate 2 168 27 2
Colony 2, Replicate 3 213 24 3
Colony-forming unit (CFU): Negative control (BBa_R0040):
Dillution 3 Dillution 4 Dillution 5
Colony 1, Replicate 1 1.44E+07 1.04E+07 2.40E+07
Colony 1, Replicate 2 9.60E+06 1.12E+07 2.40E+07
Colony 1, Replicate 3 1.58E+07 2.64E+07 1.60E+07
Colony 2, Replicate 1 2.26E+07 1.84E+07 1.60E+07
Colony 2, Replicate 2 1.71E+07 2.24E+07 2.40E+07
Colony 2, Replicate 3 1.74E+07 2.32E+07 8.00E+06
Average
  • Colony 1: 1.69E+07 CFU/ml/0.1OD
  • Colony 2: 1.88E+07 CFU/ml/0.1OD
  • Average: 1.785E+07 CFU/ml/0.1OD
  • Using conversion factor OD/Abs= 3.036
  • Conversion factor: CFU/Abs/ml= 54.34 CFU/Abs/ml

Conclusion:

Overall, the result obtained was reasonable. Among all device, device 1 reach overall highest fluorescence level while device show the lowest, the outcome is due to the different of promoter of GFP. Since the strength of promoter of device affect the expression of GFP. According to the Part Registry, promoter strength of device 1 (BBa_J23101), device 2 (BBa_J23106), device 3 (BBa_J23117), device 4 (BBa_J23100), device 5 (BBa_J23104) and device 6 (BBa_J23116) are 1791, 1185, 162, 2547, 1830 and 396 au respectively. This may explain the difference levels of GFP produced.

REFERENCES:

The 2018 International Genetically Engineered Machine. (17 July, 2018). Tracks/Measurement/Interlab study/Plate Reader Protocol. Retrieved from https://static.igem.org/mediawiki/2018/0/09/2018_InterLab_Plate_Reader_Protocol.pdf

Registry of Standard Biological Parts (2018-04-17) Retrieved from http://parts.igem.org/assembly/plates.cgi?id=5641

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