CHEMICAL INVESTIGATION OF METABOLITES PRODUCED BY MARINE PSEUDOALTEROMONAS SPP.

Abstract

In natural environments, bacteria are surrounded by other organisms such as eukaryotic phytoplankton and other bacterial species. Specialized metabolites are encoded within bacterial genomes and are expected to play a large role in mediating interactions with other cells. Furthermore, chemical communication in bacterial communities is a key component to controlling group behaviors including virulence. Marine Pseudoalteromonas spp. Produce a plethora of specialized metabolites, suggesting a reliance on the biosynthesis, secretion, and response to chemical cues. This dissertation explores the prevalence and function of signaling molecules and specialized metabolites produced by two species of Pseudoalteromonas. The first study, which is reported in chapter 2, describes the role of the quorum sensing molecule, 2-heptyl-4-quinolone (HHQ) in phytoplankton bloom dynamics. This study aims to identify the concentrations of HHQ in a coculture environment with Pseudoalteromonas galatheae A757 and the marine coccolithophore Emiliania huxleyi CCMP2090. Furthermore, this study expands on phytoplankton growth responses to the presence of A757. To further support experiments, it was verified that HHQ is stable over a 28 day incubation period at laboratory conditions that mimic the environmental parameters. When cocultured together, there are two distinct spikes in HHQ, during exponential growth phase and, more interestingly, during a second growth phase of A757 growth. We hypothesize that HHQ is coordinating bacterial phenotypes in response to E. huxleyi cell death and the availability of nutrients. The second study described in Chapter 3, is comprised of a bioinformatic analysis of Pseudoalteromonas sp. JC3 and evaluating possible avenues of probiotic effects against acute hepatopancreatic necrosis disease causing Vibrio parahaemolyticus PSU 5579, a pathogen that infects the white-leg shrimp, Litopeneus vannamei. Genes encoded for production of hydrogen peroxide, biofilm formation, production of outer membrane vesicles, and the production of specialized metabolites including darobactin and alterochromides were identified within the JC3 genome. Experiments were designed to evaluate the influence of potential routes of growth inhibition of V. parahaemolyticus PSU 5579. Interestingly, hydrogen peroxide, biofilm formation and the production of various specialized metabolites were not found to play a role in growth inhibition of V. parahaemolyticus PSU 5579. Other contributions to aquaculture, antibiotic drug discovery and undergraduate teaching manuscripts are reported in this dissertation as appendices. Citations of published manuscripts can be found at the end of this section. Appendix C outlines a LC-MS/MS experiment I developed to detect signaling molecules produced by Phaeobacter inhibens S4 (publication pending in Applied and Environmental Microbiology). I have made