Phosphoethanolamine substitution in the lipid A of Escherichia coli O157 : H7 and its association with PmrC

Abstract

This study shows that lipid A of Escherichia coli O157 : H7 differs from that of E. coli K-12 in that it has a phosphoform at the C-1 position, which is distinctively modified by a phosphoethanolamine (PEtN) moiety, in addition to the diphosphoryl form. The pmrC gene responsible for the addition of PEtN to the lipid A of E. coli O157 : H7 was inactivated and the changes in lipid A profiles were assessed. The pmrC null mutant still produced PEtN-modified lipid A species, albeit in a reduced amount, indicating that PmrC was not the only enzyme that could be used to add PEtN to lipid A. Natural PEtN substitution was shown to be present in the lipid A of other serotypes of enterohaemorrhagic E. coli and absent from the lipid A of E. coli K-12. However, the cloned pmrC O157 gene in a high-copy-number plasmid generated a large amount of PEtN-substituted lipid A species in E. coli K-12. The occurrence of PEtN-substituted lipid A species was associated with a slight increase in the MICs of cationic peptide antibiotics, suggesting that the lipid A modification with PEtN would be beneficial for survival of E. coli O157 : H7 in certain environmental niches. However, PEtN substitution in the lipid A profiles was not detected when putative inner-membrane proteins (YhbX/YbiP/YijP/Ecf3) that show significant similarity with PmrC in amino acid sequence were expressed from high-copy-number plasmids in E. coli K-12. This suggests that these potential homologues are not responsible for the addition of PEtN to lipid A in the pmrC mutant of E. coli O157 : H7. When cells were treated with EDTA, the amount of palmitoylated lipid A from the cells carrying a high-copy-number plasmid clone of pmrC O157 that resulted in significant increase of PEtN substitution was unchanged compared with cells without PEtN substitution, suggesting that the PEtN moiety substituted in lipid A does not compensate for the loss of divalent cations required for bridging neighbouring lipid A molecules.

Modulation of Hexa-Acyl Pyrophosphate Lipid A Population underEscherichia coliPhosphate (Pho) Regulon Activation

“…Also, pEtN substitution was observed in an enterohemorrhagic E. coli strain (EHEC; see Fig. 3A) (24). In our study, lipid A variants were observed in APEC strains but not in porcine ExPEC strains under low-phosphate conditions.…”

“…Since the pst mutants display PMB sensitivity, which could be caused by lipid A modifications (18,35,45), we undertook radiolabeled lipid A analyses by TLC. Because of its known TLC profile, an E. coli O157:H7 strain was used as a control (24). Its profile is similar to that of E. coli K-12 MC1061 except for an additional phosphoethanolamine (pEtN) lipid A variant (24) (Fig.…”

“…Because of its known TLC profile, an E. coli O157:H7 strain was used as a control (24). Its profile is similar to that of E. coli K-12 MC1061 except for an additional phosphoethanolamine (pEtN) lipid A variant (24) (Fig. 3A).…”

Modification of Lipooligosaccharide with Phosphoethanolamine by LptA in Neisseria meningitidis Enhances Meningococcal Adhesion to Human Endothelial and Epithelial Cells

“…The modification of the 4Ј position of the lipid A moiety of LOS (or LPS) with PEA is known to confer resistance to cationic antimicrobial peptides such as polymyxin B on N. meningitidis (41), Salmonella enterica (23), and E. coli (21). However, other biological roles of the modification have not been elucidated.…”

ArnT proteins that catalyze the glycosylation of lipopolysaccharide share common features with bacterialN-oligosaccharyltransferases

“…The lipid A backbone structure is highly conserved in most bacteria, but it is also remodeled by the addition or subtraction of components in response to environmental cues (Needham and Trent 2013). For example, covalent modification of phosphate groups in the lipid A by the addition of positively charged moieties, such as phosphoethanolamine (Kim et al 2006;Raetz et al 2007), galactosamine (Wang et al 2009), glucosamine (Marr et al 2008) and 4-amino-4-deoxy-L-arabinose (L-Ara4N) (Trent, Ribeiro, Doerrler, et al 2001;Molinaro et al 2015), reduce the overall negative charge of the molecule. These covalent modifications confer resistance to cationic antimicrobial peptides such as polymyxin B (PmB) and aminoglycoside antibiotics, and are associated with enhanced bacterial virulence (Needham and Trent 2013).…”