A D , D ‐carboxypeptidase is required for V ibrio cholerae halotolerance

Summary The biological roles of low molecular weight penicillin‐binding proteins ( LMW PBP ) have been difficult to discern in G ram‐negative organisms. In E scherichia coli , mutants lacking these proteins often have no phenotype, and cells lacking all seven LMW PBPs remain viable. In contrast, we report here that V ibrio cholerae lacking DacA ‐1, a PBP 5 homologue, displays slow growth, aberrant morphology and altered peptidoglycan ( PG ) homeostasis in Luria–Bertani ( LB ) medium, as well as a profound plating defect. DacA ‐1 alone among V . cholerae's   LMW PBPs is critical for bacterial growth; mutants lacking the related protein DacA ‐2 and/or homologues of PBP 4 or PBP 7 displayed normal growth and morphology. Remarkably, the growth and morphology of the dac A ‐1 mutant were unimpaired in LB media containing reduced concentrations of N a C l (100 mM or less), and also within suckling mice, a model host for the study of cholera pathogenesis. Peptidoglycan from the dac A ‐1 mutant contained elevated pentapeptide levels in standard and low salt media, and comparative analyses suggest that DacA ‐1 is V . cholerae's principal DD ‐carboxypeptidase. The basis for the dac A ‐1 mutant's halosensitivity is unknown; nonetheless, the mutant's survival in biochemically uncharacterized environments (such as the suckling mouse intestine) can be used as a reporter of low N a + content.