FIG. 6.

Proposed models of negative regulation of alginate production by KinB in P. aeruginosa. Mutation of kinB in wt mucA strain PAO1 causes alginate overproduction. Alginate overproduction by kinB mutants requires algB and rpoN. In model 1, we propose that mutation of kinB causes loss of expression of a periplasmic protease(s), which leads to accumulation of AlgW-activating factors. In model 2, we propose that algB and rpoN control expression of factors which can activate the AlgW protease to release repression of MucA by proteolytic degradation and activate AlgU. In either case, derepression of MucA by regulated proteolysis causes AlgU activation, which facilitates algU expression, resulting in mucoidy by upregulating the alginate biosynthetic operon. OM and IM, outer membrane and inner membrane, respectively.