Abstract:
Vibrio cholerae causes cholera in humans. During outbreaks, infections initiate due to ingestion of a small number of V. cholerae cells. Upon reaching the small intestine, V. cholerae begins to form biofilms, multicellular communities that protect bacterial cells from the host environment and the immune system. In this environment, bacteria are also exposed to host-derived antimicrobial peptides (AMPs), many of which are cationic. While AMPs are primarily studied for their bactericidal activity, their potential to modulate bacterial behavior at sublethal concentrations remains underexplored. Using an imaging guided biofilm formation model, I examined how sublethal concentrations of the NCR247 peptide might modify V. cholerae biofilm and individual cell behavior. NCR247, a cationic peptide, belongs to the broader NCR family of plant peptides that alter bacterial cell cycle and morphology during legume-rhizobia symbiosis. To my surprise, V. cholerae adopts a filamentous morphotype during the early stages of biofilm development. This morphotype has been proposed to be efficient at colonizing the host and establishing infection. Super resolution and time-lapse 20x-imaging revealed that filamentous cells developed multiple constriction sites over time and subsequently divided into shorter cells, suggesting a transient block in cell division during early growth that is relieved as cell density increases. Importantly, NCR247 suppresses V. cholerae filamentation. Using a series of NCR247 peptide variants, I identified peptide cationicity as the key determinant underlying this suppression. Consistent with this, the intestinal cationic peptide LL-37 also suppressed filamentation. Based on these results, I propose a model in which sublethal concentrations of cationic AMPs modulate V. cholerae morphological transitions by suppressing filamentation through an as yet unknown mechanism, potentially limiting V. cholerae pathogenesis.
