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 Δpst mutant, PhoB is constitutively activated and regulates the expression of genes from the Pho regulon. In E. coli O157:H7, the Δpst mutant, biofilm, and autoagglutination were increased. In the double-deletion mutant Δpst ΔphoB,

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... film 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 Δpst 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 Δpst mutant. Interestingly, waaH, encoding a glycosyltransferase associated with LPS modifications in E. coli K-12, was highly expressed in the Δpst mutant of E. coli O157:H7. Deletion of waaH from the Δpst 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 Δpst 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.