A Population-Level Analysis of Novel Antimicrobial Production Among Wild Marine Vibrio Bacteria

Pathogenic, disease-causing Vibrio bacteria are persistent in U.S. coastal waters, as made evident by recurrent outbreaks originating from contaminated seafood or exposure to beaches. An extreme Vibrio cholerae outbreak occurred in Haiti after the 2010 catastrophic earthquake where 439,000 cases of cholera were reported, and over 6,200 deaths occurred. Previously, Haiti had been cholera free for over 100 years. Interestingly, Vibrio populations (i.e., closely related isolates that cluster as distinct phylogentic groups) sampled from the same coastal waters in the absence of an outbreak typically lack virulent strains, suggesting pathogenic vibrios have a decreased fitness at the population level. A likely but unexplored factor is the ability of other vibrios, belonging to non-pathogenic groups,to synthesize compounds that antagonize nearby competitors, and likewise have the ability to resist such compounds. <p/>To this end, we propose to study antagonistic interactions among wild culturable marine bacteria using an established population-level approach under the hypothesis that pathogenic vibrios are outcompeted through population-wide interactions as a direct result of antimicrobial production by wild isolates. Preliminary results show we have identified wild strains that are capable of inhibiting growth of most other distantly related Vibrio within their proximal environment, but are themselves resistant; we refer to these isolates as 'Super Killers' (SKs). Seven SKs have been identified with differential activities and from multiple species. <p/>Here, we will 1) characterize the SK antimicrobial/resistance mechanisms, 2) investigate SK dynamics over time, and 3) test their ability to directly inhibit pathogens. We have developed and optimized a working genetic system for the manipulation of Vibrio environmental isolates (i.e., mutagenesis, gene deletions/insertions, and ectopic expression), such that we are able to efficiently identify and characterize the genetic loci involved in each compound's synthesis and corresponding resistance. <p/>In preliminary investigations with a single SK, we have identified a candidate genetic locus that encodes a putatively novel non-ribosomal peptide synthetase with antimicrobial function, and have begun to characterize the gene region and products, and associated resistance mechanism. This work has research merit in the identification of natural antimicrobial compounds and resistance mechanisms with the potential for new leads on drug development. The research plan has been designed in consideration of a high level of student involvement and training in an important and comprehensive study designed to characterize naturally occurring antimicrobial products and resistance mechanisms. The specific research itself offers much direct, hands-on involvement, using methodologies that are relatively straightforward, with little risk, and with a high likelihood of success. <p/>Finally, the project has been designed to impact student exposure to a range of topics (i.e., factors that influence pathogenicity, emergence of pathogens, antimicrobial compounds/resistance mechanisms, population-level interactions, etc.) and offers a smooth transition into a variety of biomedical interests.