Programmed bacterial lysis in vivo alters host immune responses and microbial pathogenesis

Vibrio cholerae injects toxic type VI secretion system (T6SS) effectors to lyse sensitive intestinal commensals, but how this bacterial antagonism enhances mucosal host immune responses and its pathogenicity remains unknown. To mimic T6SS-mediated killing, we engineered V. cholerae lysis strains by using CRISPR interference (CRISPRi) to knockdown essential genes in peptidoglycan biogenesis or lipopolysaccharide (LPS) transport. Our results indicate that controlled bacterial lysis in vivo leads to divergent mucosal immune responses that directly modulate colonization and pathogenicity of a bystander, non-lysing V. cholerae ΔT6SS strain. Mass spectrometric analysis of the lysis debris revealed proinflammatory muropeptides correlating with these changes. We confirmed that oral co-administration of a synthetic peptidoglycan-derived metabolite with a V. cholerae ΔT6SS mutant, but not the wild type, shows dramatic enhancement of disease symptoms. These findings show that intestinal exposure to discrete bacterial cell wall metabolites can differentially modulate host innate immune responses and consequently bacterial pathogenesis.