Date of Award
Doctor of Philosophy in Pharmaceutical Sciences
Biomedical and Pharmaceutical Sciences
David C. Rowley
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 contributions to two manuscripts involving human pathogens. In 2021, a publication in the Journal of Antibiotics outlined the discovery, synthesis, and putative mechanism of action of a small molecule antibiotic against a multi-drug resistant strain of Acinetobacter baumannii.1 A screen of the University of Rhode Island, Principle Rhode Island Secondary Metabolite (PRISM) library led to the discovery of a known molecule produced by the tulip popular that has anti-Staphylococcus aureus properties. This paper, pending publication the Journal of Natural Products, describes structure activity relationships of a class of sesquiterpene lactones and their bioactivity.
For two semesters in graduate school, I had the pleasure of assisting Dr. Matthew Bertin in teaching an undergraduate research course, BPS 451: Techniques in Medicinal Chemistry and Molecular Biology. In this course, students are immersed in Natural Product Chemistry and utilize complex techniques including HPLC and LCMS. Two publications (1 published, 1 pending publication) in the ACS Journal of Chemical Education describe the pipeline, methods, and techniques used for a successful lab-based semester.2
- Deering, RW, Whalen KE, Alvarez I, Daffinee K, Beganovic M, LaPlante KL, Kishore S, Zhao S, Cezairliyan B, Yi S, Rosario M, Mincer TJ, Rowley DC. 2021. Identification of a bacteria-pro duced benzisoxazole with antibiotic activity against multi-drug resistant Acinetobacter baumannii. J. Antibiot. 74, 370–380. doi: 10.1038/s41429-021-00412-7
- Kirk, RD, Carro MA, Wu C, Aldine MJ, Wharton AM, Goldstein DG, Rosario MD, Gallucci GM, Zhao Y, Leibovitz E, Bertin MJ. 2020. Integrating Natural Product Chemistry Workflows into Medicinal Chemistry Laboratory Training: Building the PRISM Library and Cultivating Independent Research. J. Chem. Educ. 98, 410–415. doi: 10.1021/acs.jchemed.0c00396
Rosario, Margaret, "CHEMICAL INVESTIGATION OF METABOLITES PRODUCED BY MARINE PSEUDOALTEROMONAS SPP." (2022). Open Access Dissertations. Paper 1368.