Novel coordination of lipopolysaccharide modifications in Vibrio cholerae promotes CAMP resistance

Abstract

Summary In the environment and during infection, the human intestinal pathogen Vibrio cholerae must overcome noxious compounds that damage the bacterial outer membrane. The El Tor and classical biotypes of O1 V. cholerae show striking differences in their resistance to membrane disrupting cationic antimicrobial peptides (CAMPs), such as polymyxins. The classical biotype is susceptible to CAMPs, but current pandemic El Tor biotype isolates gain CAMP resistance by altering the net charge of their cell surface through glycine modification of lipid A. Here we report a second lipid A modification mechanism that only functions in the V. cholerae El Tor biotype. We identify a functional EptA ortholog responsible for the transfer of the amino-residue phosphoethanolamine (pEtN) to the lipid A of V. cholerae El Tor that is not functional in the classical biotype. We previously reported that mildly acidic growth conditions (pH 5.8) downregulate expression of genes encoding the glycine modification machinery. In this report, growth at pH 5.8 increases expression of eptA with concomitant pEtN modification suggesting coordinated regulation of these LPS modification systems. Similarly, efficient pEtN lipid A substitution is seen in the absence of lipid A glycinylation. We further demonstrate EptA orthologs from non-cholerae Vibrio species are functional.

Acidic pH promotes lipopolysaccharide modification and alters colonization in a bacteria–animal mutualism

“…Acid‐induced genes included those that encode several predicted outer membrane porins, including the major outer membrane proteins, OmpU and OmpC, as well as the homolog of a phosphoethanolamine transferase, EptA (also known as PmrC, or polymyxin resistance protein C). EptA homologs have previously been shown to modify the structure of the lipid A portion of lipopolysaccharide (LPS) in Gram‐negative bacteria like Salmonella typhimurium and certain strains of Vibrio cholerae (Lee et al , ; Herrera et al , ). We verified the differential transcription of eptA and ompC (VF_1795) at different growth pHs using qRT‐PCR (Fig.…”

“…Ethanolamine transferase‐catalyzed lipid A modification is a conserved mechanism for resisting host innate immunity derived cationic antimicrobial peptides (CAPs) among diverse pathogenic and mutualistic microbes, including Vibrio spp. (Beceiro et al , ; Chen and Groisman, ; Cullen et al , ; Herrera et al , ). Moreover, we show that ethanolamine transferase activity increases the infectivity of V. fischeri.…”

AlmG, responsible for polymyxin resistance in pandemic Vibrio cholerae, is a glycyltransferase distantly related to lipid A late acyltransferases

“…5 and 6). Similarly V. cholerae EptA is capable of phosphoethanolamine transfer to glycinylated substrates (34). Thus phosphoethanolamine and glycine transfer does not occur at the level of enzymatic substrate specificity.…”

“…Our laboratory recently reported that V. cholerae El Tor has maintained a second LPS modification to promote polymyxin resistance through the addition of phosphoethanolamine residues to lipid A phosphate groups (34). The Vibrio EptA homolog is similar to pEtN transferases found in other pathogens, including Neisseria meningitidis, Salmonella enterica, Campylobacter jejuni, and pathogenic E. coli.…”

“…However, there is coordinated control of LPS glycine and phosphoethanolamine modifications in V. cholerae at the transcriptional level. The responsible regulatory network has not been sorted out, but we do know that expression of eptA is not controlled by the AlmEFG transcriptional regulator VprA (34,36).…”