New functions for the second messenger cyclic-di-GMP in E. coli




Hwang, Yunesahng

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c-di-GMP is one of the most versatile second messengers in bacteria. It controls a variety of bacterial cellular processes, primarily promoting biofilms while inhibiting motility. c-di-GMP is synthesized from two GTP molecules by diguanylate cyclases (DGCs). Bacteria encode multiple DGCs that are activated by specific environmental signals. Their catalytic activity is modulated by c-di-GMP binding to autoinhibitory sites (I-sites). In E. coli, the most potent DGCs is YfiN, which lacks I sites. Instead, YfiN activity is repressed by periplasmic YfiR, which is inactivated by redox stress to produce c-di-GMP, inhibiting swimming and activating biofilm production. A second envelope stress causes YfiN to relocate to the mid-cell to inhibit cell division by interacting with the division machinery. Here, we report third function for YfiN, where cell growth is inhibited without YfiN relocating to the division site. This action of YfiN is only observed when the bacteria are cultured on gluconeogenic carbon sources, and is dependent on absence of I sites. Arrested cells are tolerant to a wide range of antibiotics. We show that the likely cause of growth arrest is depletion of cellular GTP from unregulated synthesis of c-di-GMP, explaining the dependence of growth arrest on gluconeogenic carbon sources that exhaust more GTP during production of glucose. This is the first report of c-di-GMP-mediated growth arrest by altering metabolic flow. We have also discovered a new role for c-di-GMP in regulating swarming motility, wherein bacteria move over semi-solid surfaces as a collective. This movement is driven by flagella and facilitated by secretion of surfactants and wetting agents, the latter typically composed of polysaccharides. Having adequate water on the surface is required for flagella to work. We show that contrary to the canonical role of c-di-GMP in inhibiting flagella-driven swimming, c-di-GMP is required for swarming in E. coli. Our data suggest that c-di-GMP may positively regulate the production of colanic acid, a polysaccharide that could serve as a wetting agent. This is the first report of c-di-GMP being required for motility.


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