PHENOTYPIC HETEROGENEITY IN SUGAR UTILIZATION BY E. COLI

The PTS regulates sugar uptake and metabolism in almost all bacteria. We have previously shown that the major PTS proteins, EI and HPr, which constitute the control center of the PTS system, localize to the E. coli cell poles independent of each other. We now monitored the localization of EI polar clusters, as well as diffuse molecules, in space and time during the lifetime of E. coli cells. We found that EI distribution and cluster dynamics varies among cells in a population, and that the cluster speed inversely correlates with cluster size. In growing cells, EI is not assembled into clusters in almost 40% of the cells, and the clusters in most remaining cells dynamically relocate within the pole region or between the poles. In non-growing cells, the fraction of cells that contain EI clusters is significantly higher, and dispersal of these clusters is often observed shortly after exiting quiescence. Later, during growth, EI clusters stochastically re-form by assembly of pre-existing dispersed molecules at random time points. Using a fluorescent glucose analog, we found that EI function inversely correlates with clustering and with cluster size. Thus, activity is exerted by dispersed EI molecules, whereas the polar clusters serve as a reservoir of molecules ready to act when needed. In agreement with that, EI is present in its diffuse form in cells harboring an HPr mutant, which binds irreversibly to EI, indicating that the diffuse form associates with HPr and, hence, is the active form. Taken together our findings highlight the spatiotemporal distribution of EI as a novel layer of regulation that contributes to the population phenotypic heterogeneity with regard to sugar metabolism, seemingly conferring a survival benefit.