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Team:NJU-QIBEBT/Indicator module
3. Indicator module
In this module, we try to figure out a method to monitor the fatty acids producing status. Specifically, not only could our E.coil automatically “inform” us of when fatty acids have been produced greatly, but it could also “show” us the relative concentration of fatty acids compared to control E.coli. To fulfill this objective, we need to find out something sensitive to fatty acids amounts in E.coli. Thus, we noticed the native regulatory system in E.coli fatty acids metabolism.
Working principle
In E.coli, the fad genes family is responsible for fatty acid degradation while the genes family fab works in the synthetic pathway. The protein FadR is a regulator. Generally, it binds to the promoters of fadD and fabB, and works as repressor and activator, respectively. In the absence of long chain acyl-CoA, the intermediate product of fatty acid synthesis, FadR will repress the fad regulon, activating the transcription of fabB and starting the fatty acid synthesis. Otherwise, the binding of long chain acyl-CoA to FadR will dramatically change the structure of this protein and release it from the operator site. Then the fad regulon transcription increases whereas that of fabB decreases. In this case, redundant fatty acids can be degraded for other usage.
Our circuit
Based on this, we built an indicator structure similar to traffic light by introduced the gfp and rfp genes (see picture 5). As you see, pfadD and pfabB were the promoters of fadD and fabB which we isolated from wide-type E.coli. After assembling them with two fluorescent genes at their downstream, they could regulate the transcription of rfp and gfp. When high concentration of fatty acid have been produced, FadR would dissociate from the binding site and the “red light" would be turned on (RFP would be expressed). In contrast, when the concentration of fatty acid is low, FadR tightly binds to the operator site and the green light will be turned on (with GFP expression).
Reference
1. Yasutaro F, Hiroshi M, Kazutake H: Regulation of fatty acid metabolism in bacteria. Molecular Microbiology 2007, 66(4):829–839
2. Liu H, Yu C, Feng D, Cheng T, Meng X, Liu W, Zou H, Xian M: Production of extracellular fatty acid using engineered Escherichia coli. Microbial Cell Factories 2012, 11:41-53
3. Yasutaro F, Hiroshi M, Kazutake H: Regulation of fatty acid metabolism in bacteria. Molecular Microbiology 2007, 66(4):829–839
4. Feng Y, Cronan JE: Crosstalk of Escherichia coli FadR with Global Regulators in Expression of Fatty Acid Transport Genes. PLOS ONE 7(9): e46275
