Fig 7.

Model for Sal4-induced EPS production and biofilm formation. (A) Schematic linear depiction of the structure of YeaJ, highlighting the putative N-terminal signal sequence, periplasmic Cache domain, a transmembrane (TM) domain, and the GGDEF domain; (B) ClustalW-sequence alignment of the Cache domains of YeaJ from S. Typhimurium (ST) and E. coli (Ec). (C) Proposed mechanism for YeaJ-mediated c-di-GMP signal transduction in S. Typhimurium in response to Sal4. Sal4 binding to the O-Ag results in OM stress, including a transient reduction in the PMF. We propose that the Cache domain of YeaJ senses Sal4-induced changes in membrane integrity and, in turn, activates the GGDEF domain of YeaJ to produce c-di-GMP. Elevated levels of c-di-GMP stimulate EPS production and reduce both bacterial motility and T3S. We speculate that the cognate phosphodiesterase (PDE) YhjH degrades the c-di-GMP produced by YeaJ.