New facet of non-O1/non-O139 Vibrio cholerae hemolysin A: a competitive factor for the environmental niche

Abstract

Different serogroups of Vibrio cholerae may inhabit the same ecological niche. However, serogroup O1/O139 strains are rarely isolated from their ecological sources. Quite plausibly, the non-O1/non-O139 vibrios and other bacterial species suppress growth of the O1/O139 that shares the same niche. Our bacterial inhibition assay data indicated that certain non-O1/non-O139 strains used a contact-dependent type VI secretion system (T6SS) to suppress growth of the O1 El Tor, N16961 pandemic strain. Meanwhile, comparative proteomics of the O1 and the suppressive non-O1/non-O139 co-cultured in the simulated natural aquatic microcosm showed that SecB and HlyD were upregulated in the latter. The HlyD-related effective factor was subsequently found to be HlyA. However, not all hlyA-positive-non-O1/non-O139 strains mediated growth suppression of the N16961 V. cholerae; only the strains harboring intact cluster I HlyA could exert this activity. The demolition feature of the HlyA is located in the ricin-like lectin domain (β-Trefoil) which plays an important role in the target cell binding. In conclusion, the results of this study indicated that non-O1/non-O139 V. cholerae suppressed the growth of the O1 pandemic strain using contact-dependent T6SS as well as secreting the O1 − detrimental hemolysin A during their co-persistence in the aquatic habitat.

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