The cell division factor ZapB is required for bile resistance in Salmonella enterica

Abstract

A gene annotated as yiiU in the genome of Salmonella enterica serovar Typhimurium encodes a protein homologous to E. coli ZapB, a non-essential cell division factor involved in Z-ring assembly. ZapB- null mutants of S. enterica are bile-sensitive. The ZapB protein is degraded in the presence of sodium deoxycholate (DOC), and degradation appears to involve the Lon protease. The amount of zapB mRNA increases in the presence of a sublethal concentration of DOC. This increase is not caused by upregulation of zapB transcription but by increased stability of zapB mRNA. DOC-induced increase of the zapB transcript is suppressed by an hfq mutation, suggesting the involvement of a small regulatory RNA. We provide evidence that such sRNA is MicA. Increased stability of zapB mRNA in the presence of DOC may counter degradation of bile-damaged ZapB, thus providing sufficient level of functional ZapB protein to permit Z-ring assembly in the presence of bile.\n\nIMPORTANCEBile salts have bactericidal activity as a consequence of membrane disruption, protein denaturation and DNA damage. However, intestinal bacteria are resistant to bile. Envelope structures such as the lipopolysaccharide and the enterobacterial common antigen act as barriers that reduce intake of bile salts. Remodelling of the outer membrane and the peptidoglycan, activation of efflux pumps, and upregulation of stress responses also contribute to bile resistance. This study adds the cell division factor ZapB (and presumably the Z-ring) to the list of cellular functions involved in bile resistance.