Escherichia coli genes regulated by cell-to-cell signaling

Utilizing the bicistronic reporter transposon mini-Tn5 lacZ-tet/1, we have identified lacZ fusions to four Escherichia coli genes/operons that are strongly activated by the accumulation of self-produced extracellular signals. These fusions were designated cma9, cma48, cma113, and cma114 for conditioned medium activated. Each of the cma fusions was expressed in a growth phase-dependent manner, and the presence of conditioned medium from a stationary phase E. coli culture resulted in the premature activation of these fusions in cells at early to mid-logarithmic phase. The cma48 and cma114 fusions were dependent on RpoS for growth phase expression and response to extracellular factors. The extracellular factors that activated the cma9, cma48, and cma114 fusions were produced in both rich complex and defined minimal media. The cma fusions were shown to be within the cysK (cma9), astD (cma48), tnaB (cma113), and gabT (cma114) genes. These genes function in the uptake, synthesis, or degradation of amino acids that yield pyruvate and succinate.