Differential Requirement for PBP1a and PBP1b inIn VivoandIn VitroFitness of Vibrio cholerae

Abstract

ABSTRACTWe investigated the roles of theVibrio choleraehigh-molecular-weight bifunctional penicillin binding proteins, PBP1a and PBP1b, in the fitness of this enteric pathogen. Using a screen for synthetic lethality, we found that theV. choleraePBP1a and PBP1b proteins, like theirEscherichia colihomologues, are each essential in the absence of the other and in the absence of the other's putative activator, the outer membrane lipoproteins LpoA and LpoB, respectively. Comparative analyses ofV. choleraemutants suggest that PBP1a/LpoA ofV. choleraeplay a more prominent role in generating and/or maintaining the pathogen's cell wall than PBP1b/LpoB.V. choleraelacking PBP1b or LpoB exhibited wild-type growth under all conditions tested. In contrast,V. choleraelacking PBP1a or LpoA exhibited growth deficiencies in minimal medium, in the presence of deoxycholate and bile, and in competition assays with wild-type cells bothin vitroand in the infant mouse small intestine. PBP1a pathway mutants are particularly impaired in stationary phase, which renders them sensitive to a product(s) present in supernatants from stationary-phase wild-type cells. The marked competitive defect of the PBP1a pathway mutantsin vivowas largely absent when exponential-phase cells rather than stationary-phase cells were used to inoculate suckling mice. Thus, at least forV. choleraePBP1a pathway mutants, the growth phase of the inoculum is a key modulator of infectivity.