Escherichia coli O157:H7 responds to phosphate starvation by modifying LPS involved in biofilm formation

In open environments such as water, enterohemorrhagic Escherichia coli O157:H7 responds to inorganic phosphate (Pi) starvation by inducing the Pho regulon controlled by PhoB. The phosphate-specific transport (Pst) system is the high-affinity Pi transporter. In the Δ pst mutant, PhoB is constitutively activated and regulates the expression of genes from the Pho regulon. In E. coli O157:H7, the Δ pst mutant, biofilm, and autoagglutination were increased. In the double-deletion mutant Δ pst Δ phoB , biofilm and autoagglutination were similar to the wild-type strain, suggesting that PhoB is involved. We investigated the relationship between PhoB activation and enhanced biofilm formation by screening a transposon mutant library derived from Δ pst mutant for decreased autoagglutination and biofilms mutants. Lipopolysaccharide (LPS) genes involved in the synthesis of the LPS core were identified. Transcriptomic studies indicate the influence of Pi-starvation and pst mutation on LPS biosynthetic gene expression. LPS analysis indicated that the O-antigen was deficient in the Δ pst mutant. Interestingly, waaH , encoding a glycosyltransferase associated with LPS modifications in E. coli K-12, was highly expressed in the Δ pst mutant of E. coli O157:H7. Deletion of waaH from the Δ pst mutant and from the wild-type strain grown in Pi-starvation conditions decreased the biofilm formation but without affecting LPS. Our findings suggest that LPS core is involved in the autoagglutination and biofilm phenotypes of the Δ pst mutant and that WaaH plays a role in biofilm in response to Pi-starvation. This study highlights the importance of Pi-starvation in biofilm formation of E. coli O157:H7, which may affect its transmission and persistence.