Evidence for Involvement of the Z-Ring Assembly Factors ZapA and ZapB in Resistance to Bile.

Genes annotated as and in the genome of serovar Typhimurium encode proteins homologous to cell division factors ZapA and ZapB, respectively. ZapA and ZapB mutants of are bile-sensitive. The amount of mRNA increases in the presence of a sublethal concentration of sodium deoxycholate (DOC) while mRNA remains unaffected. Increased mRNA level in the presence of DOC is not caused by upregulation of transcription but by increased stability of mRNA. This increase is suppressed by an mutation, suggesting the involvement of a small regulatory RNA. We provide evidence that such sRNA is MicA. The ZapB protein is degraded in the presence of DOC, and degradation appears to involve the Lon protease. We propose that increased stability of mRNA in the presence of DOC may counter degradation of bile-damaged ZapB, thereby providing sufficient level of functional ZapB protein to permit Z-ring assembly in the presence of bile.