FIGURE 8.

Proposed model for the cabABC regulatory network. A regulatory network comprised of the three transcriptional regulators BrpR, BrpT, and BrpS controls expression of the cabABC operon. Intracellular c-di-GMP levels can be altered in response to various environmental signals. Under elevated intracellular c-di-GMP levels, BrpR activates brpT and cabABC in a sequential cascade. BrpT and BrpS constitute a negative feedback loop for brpT regulation, where BrpT activates brpS, but BrpS represses brpT. BrpT and BrpS also form a feedforward loop for positive regulation of cabABC. CabA is secreted through a type I secretion system comprised of CabB, CabC, and the outer membrane protein TolC. CabA in the extracellular matrix contributes to development of robust biofilm structures and rugose colony morphology in cooperation with brp-exopolysaccharide. The red dots represent c-di-GMP molecules.