Bet-hedging and communication in E. coli? - Investigations of heterogeneous gene expression of carbohydrate uptake systems

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Bistable expression of the lac operon has been known for quite a long time. Although the molecular mechanisms of this expression pattern provoked by gratuitous inducers have been clarified, no investigations are available that deal with induction by the original substrate lactose or that try to elucidate the potential benefit of this expression. The project at hand will analyze heterogeneity of lac operon expression after induction with low levels of lactose, the natural substrate that is actively metabolized by the cells. A potential growth benefit of induced cells will be investigated. Another important aspect of the project will be the analysis of cAMP in heterogeneous lac operon expression. It is well established that cAMP represents a hunger signal in E. coli and influences the expression of most carbohydrate uptake systems. Nevertheless the reasons underlying cAMP control have never been investigated in detail. As most cAMP is expelled into the medium this molecule has the potential to serve as a hunger signal not only at the cellular but also at the population level. The investigations carried out in the frame of this project will deal with this topic. Lastly, we will analyze induction properties of carbohydrate uptake systems if cells are subjected to low concentrations of two different carbohydrates. Different induction patterns are possible, cells that induce uptake of both substrates, of one substrate or of none. The results promise to give interesting insights into possible bet-hedging strategies and sociobiology of E. coli.