Regulation of waaH by PhoB during Pi Starvation Promotes Biofilm Formation by Escherichia coli O157:H7.

ABSTRACT

In open environments such as water, enterohemorrhagic Escherichia coli O157H7 responds to inorganic phosphate (Pi) starvation by inducing the Pho regulon controlled by PhoB. This activates the phosphate-specific transport (Pst) system that contains a high-affinity Pi transporter. In the Δpst mutant, PhoB is constitutively activated and regulates the expression of genes in the Pho regulon. Here, we show that Pi starvation and deletion of the pst system enhance E. coli O157H7 biofilm formation. Among differentially expressed genes of EDL933 grown under Pi starvation conditions and in the Δpst mutant, we have found that a member of the PhoB regulon, waaH, predicted to encode a glycosyltransferase, was highly expressed. Interestingly, WaaH contributed to biofilm formation of E. coli O157H7 during both Pi starvation and in the Δpst mutant. In the Δpst mutant, the presence of waaH was associated with lipopolysaccharide (LPS) R3 core type modifications, whereas in E. coli O157H7, waaH overexpression had no effect on LPS structure during Pi starvation. Therefore, waaH participates in E. coli O157H7 biofilm formation during Pi starvation, but its biochemical role remains to be clarified. This study highlights the importance of the Pi starvation stress response to biofilm formation, which may contribute to the persistence of E. coli O157H7 in the environment.IMPORTANCE Enterohemorrhagic Escherichia coli O157H7 is a human pathogen that causes bloody diarrhea that can result in renal failure. Outside of mammalian hosts, E. coli O157H7 survives for extended periods of time in nutrient-poor environments, likely as part of biofilms. In E. coli K-12, the levels of free extracellular Pi affect biofilm formation; however, it was unknown whether Pi influences biofilm formation by E. coli O157H7. Our results show that upon Pi starvation, PhoB activates waaH expression, which favors biofilm formation by E. coli O157H7. These findings suggest that WaaH is a target for controlling biofilm formation. Altogether, our work demonstrates how adaptation to Pi starvation allows E. coli O157H7 to occupy different ecological niches.