The Rcs-regulated colanic acid capsule maintains membrane potential in Salmonella enterica serovar Typhimurium

Abstract

The Rcs phosphorelay and Psp (phage shock protein) systems are envelope stress responses that are highly conserved in γ-proteobacteria. The Rcs regulon was found to be strongly induced during metal deprivation of Salmonella enterica serovar Typhimurium lacking the Psp response. Nineteen genes activated by the RcsA-RcsB response regulator comprise an operon responsible for production of colanic acid capsular polysaccharide, which promotes biofilm development. Despite more than half a century of research, the physiological function of colanic acid has remained elusive. In this study we provide evidence that Rcs-dependent colanic acid production maintains the transmembrane electrical potential (Δψ) and proton motive force (PMF) in cooperation with the Psp response. Production of negatively-charged exopolysaccharide covalently bound to the outer membrane may enhance the surface potential by increasing the local proton concentration. This provides a unifying mechanism to account for diverse Rcs/colanic acid-related phenotypes, including susceptibility to membrane-damaging agents and biofilm formation. This work provides a new and fundamental insight into bacterial physiology.