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

Abstract

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 {Delta}pst mutant, PhoB is constitutively activated and regulates the expression of genes from the Pho regulon. In E. coli O157:H7, the {Delta}pst mutant, biofilm, and autoagglutination were increased. In the double-deletion mutant {Delta}pst {Delta}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 {Delta}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 {Delta}pst mutant. Interestingly, waaH, encoding a glycosyltransferase associated with LPS modifications in E. coli K-12, was highly expressed in the {Delta}pst mutant of E. coli O157:H7. Deletion of waaH from the {Delta}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 {Delta}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. IMPORTANCEEnterohemorrhagic Escherichia coli O157:H7 is a human pathogen responsible for bloody diarrhea and renal failures. In the environment, O157:H7 can survive for prolonged periods of time under nutrient-deprived conditions. Biofilms are thought to participate in this environmental lifestyle. Previous reports have shown that the availability of extracellular inorganic phosphate (Pi) affected bacterial biofilm formation; however, nothing was known about O157:H7 biofilm formation. Our results show that O157:H7 membrane undergoes modifications upon PhoB activation leading to increased biofilm formation. A mutation in the Pst system results in reduced amount of the smooth type LPS and that this could influence the biofilm composition. This demonstrates how the E. coli O157:H7 adapts to Pi starvation increasing its ability to occupy different ecological niches.