Vibrio fischeri Amidase Activity Is Required for Normal Cell Division, Motility, and Symbiotic Competence.

-Acetylmuramoyl-l-alanine amidases are periplasmic hydrolases that cleave the amide bond between -acetylmuramic acid and alanine in peptidoglycan (PG). Unlike many Gram-negative bacteria that encode redundant periplasmic amidases, appears to encode a single protein that is homologous to AmiB of We screened a transposon mutant library for strains altered in biofilm production and discovered a biofilm-overproducing strain with an insertion in (). Further characterization of biofilm enhancement suggested that this phenotype was due to the overproduction of cellulose, and it was dependent on the cellulose synthase. Additionally, the mutant was nonmotile, perhaps due to defects in its ability to septate during division. The amidase mutant was unable to compete with the wild type for the colonization of 's symbiotic host, the squid In single-strain inoculations, host squid inoculated with the mutant eventually became colonized but with a much lower efficiency than in squid inoculated with the wild type. This observation was consistent with the pleiotropic effects of the mutation and led us to speculate that motile suppressors of the mutant were responsible for the partially restored colonization. In culture, motile suppressor mutants carried point mutations in a single gene (), resulting in a partial restoration of wild-type motility. In addition, these point mutations reversed the effect of the mutation on cellulosic biofilm production. These data are consistent with AmiB possessing amidase activity; they also suggest that AmiB suppresses cellulosic biofilm formation but promotes successful host colonization. Peptidoglycan (PG) is a critical microbe-associated molecular pattern (MAMP) that is sloughed by cells of during symbiotic colonization of squid. Specifically, this process induces significant remodeling of a specialized symbiotic light organ within the squid mantle cavity. This phenomenon is reminiscent of the loss of ciliated epithelium in patients with whooping cough due to the production of PG monomers by Furthermore, PG processing machinery can influence susceptibility to antimicrobials. In this study, we report roles for the PG amidase AmiB, including the beneficial colonization of squid, underscoring the urgency to more deeply understand PG processing machinery and the downstream consequences of their activities.