Abstract
We report that the Bacillus subtilis exopolysaccharide (EPS) is a signaling molecule that controls its own production. EPS synthesis depends on a tyrosine kinase that consists of a membrane component (EpsA) and a kinase component (EpsB). EPS interacts with the extracellular domain of EpsA, which is a receptor, to control kinase activity. In the absence of EPS, the kinase is inactivated by autophosphorylation. The presence of EPS inhibits autophosphorylation and instead promotes the phosphorylation of a glycosyltransferase in the biosynthetic pathway, thereby stimulating the production of EPS. Thus, EPS production is subject to a positive feedback loop that ties its synthesis to its own concentration. Tyrosine kinase-mediated self-regulation could be a widespread feature of the control of exopolysaccharide production in bacteria.