Fast Modulation of Phenotypic Diversity in Bacterial Chemotaxis*

A central question in cell biology is how cell populations deal with ever-changing environments. It has been shown that gene regulatory networks can modulate in an environment-dependent manner not only the average phenotype, but also its diversity within isogenic populations. Here, we demonstrate that cells can also tune the level of phenotypic diversity much more rapidly than is possible by gene expression, using covalent modification of signaling proteins. In the E.coli chemotaxis pathway, we find that the diversity of a key sensory parameter, the response sensitivity, is modulated depending on the presence or absence of ambient chemoattractant molecules. We show how this diversity tuning originates from an environment-dependent mapping between the sensitivity phenotype and the standing cell-to-cell variation in the number of allosterically-coupled receptors. This diversity tuning enhances the population’s readiness for uncertain future signals in the absence of any signal, but allows the population to rapidly switch to tracking the signal once it is perceived.