On the Shoulder of Those Who Came Before Us
After analyzing the experiment result for our pH-sensing system, we have concluded that we should try to improve the pH-sensing device based on gadA promoter which is constructed by 2016 iGEM Dundee team, PgadA (BBa_K1962013). We found out that although PgadA can be induced under neutral and weak acidic condition, the fluorescence intensity is too low to be observed. We planned to increase the fluorescence intensity and shorten the time interval of induction. Thus, we added a RiboJ sequence at the downstream of the PgadA.
Based on our research, RiboJ was first described as an insulator in genetic construct but there has no any data shown this insulation affected the downstream genetic parts. The mechanism of RiboJ is that the upstream sequence, as well as RiboJ sequence, will cleave after the transcription. The cleavage of promoter and RiboJ sequence aids the design of predictable genetic constructs. The 2016 iGEM William and Mary team has reported that RiboJ could increase the expression of the downstream gene. Hence, we decided to enhance the expression of PgadA by adding RiboJ at the downstream of promoter gadA.
To determine the function and compare the improvement of the parts, we have measured the fluorescence intensity (fluorescence (a.u.) / O.D.600) of the construct with and without RiboJ in different pH environment. We incubated the bacteria in pH adjusted M9 medium and measure the fluorescence intensity (absorbance: 480nm, excitation: 510 nm) in a short period of time. The pH value of M9 medium is adjusted with 1M HCl.
Fig 2. The fluorescence of PgadA and PgadA-RiboJ in pH 6 and pH 7.
We observe that with the RiboJ sequence, the fluorescence intensity has risen dramatically at the 14th hour. We also compare the fluorescence at 3rd, 6th, and 9th hour. The fluorescence of the strain that contains RiboJ is more than that does not contain RiboJ. We can conclude that by adding the RiboJ sequence to the construct, the expression of fluorescence protein is increased. We can also conclude that RiboJ could also strengthen the signal and increase the specificity of the downstream gene of it. We improve the PgadA part so the difference of the surrounding pH condition can be observed easier.
- Clifton, Kalen P, et al. “The Genetic Insulator RiboJ Increases Expression of Insulated Genes.” Sept. 2018, doi:10.1101/317875.
- 2016 iGEM Dundee team
- 2016 iGEM William and Mary