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E-coli (or any other cells) require growth media, and it follows known growth curve due to limited amount of nutrient in the media. So, either the media should be changed to fresh ones or timely subculture is necessary. Such process causes no trouble in the lab or during research, but now that we are trying to introduce e-coli with many functions to the real world. Therefore, e-coli now needs to overcome its limited life time in the given growth media.
Growth media will always contain limited amount of nutrient, so controlling the growth of e-coli would be one solution. According to growth curve, bacteria grow exponentially until they reach a stationary phase, where bacteria begin to exhaust limited resource and growth rate becomes equal to death rate. What if we intercept this normal growth? We would like to propose a system derived from quorum sensing that can regulate bacterial growth. If this system is applied, instead of growing until they exhaust the resource, bacteria will self-regulate its growth at certain concentration so the resource will be used at a controlled level.
Quorum sensing is an intercellular communication mechanism in which gene expression is regulated by cell population density. We modified this mechanism so that E.coli population can be regulated by its own density. When E.coli genes are expressed, AHL is produced. Our modified quorum sensing uses AHL as the sensor to recognize the density of E.coli population.
The IPTG on the growth media activates LuxI gene of E.coli. This activation synthesizes a molecule called AHL. AHL then binds to LuxR which is induced by other inducer (arabinose for instance). The LuxR-AHL conjugate then can stimulate pLuxR to promote the expression of CcdB. The expression of CcdB will then induce cell death.
So by controlling the concentration of two inducing molecules (IPTG and arabinose) we can find an optimal combination that can appropriately modify the growth curve so that bacteria can survive in a same medium for longer time. Also, if we go to next step, we can find a balance where bacteria survive for appropriate time and still possess good amount of expression.
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