MgrB affects the acid stress response of Escherichia coli by modulating the expression of iraM

Although MgrB is established to be a feedback inhibitor of the PhoP/Q system in Escherichia coli, the biological functions of MgrB remain largely unknown. To explore new functions of MgrB, a comparative transcriptome analysis was performed (E. coli K-12 W3110 ΔmgrB vs E. coli K-12 W3110). The results showed that many genes involved in acid stress are upregulated, suggesting that MgrB is related to acid sensitivity in E. coli. The survival rates under acid stress of the ΔmgrB mutant and wild-type showed that deletion of mgrB resulted in acid resistance. According to previous research, we deleted phoP, phoQ and iraM in the ΔmgrB mutant, and found that further deletion of phoP/phoQ only partially restored acid sensitivity. Additionally, we found that deletion of mgrB resulted in increased accumulation of RpoS during the exponential growth phase, which could be blocked by further deletion of iraM. Mutation of iraM or rpoS completely suppressed the effect of mgrB mutation on acid resistance. Taken together, the data suggest that MgrB affects the acid resistance of E. coli by modulating the expression of iraM, but not completely through PhoP/Q. This indicates that MgrB may have other protein interactors aside from PhoQ, which merits further investigation.