Date of Award
2026
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Biological and Environmental Sciences
Department
Biological Sciences
First Advisor
Marta Gomez-Chiarri
Abstract
Oysters are a commonly farmed shellfish that are economically and environmentally important; however, their populations have significantly diminished. Restoration of oyster populations involves growth in hatcheries to seed and restore dwindling populations in wild ecosystems. Both in hatcheries and in the wild, oysters face diseases that can affect multiple stages of their life. Vibriosis, caused by various pathogenic Vibrio species, is a major disease affecting oysters at the larval stage. A rise in Vibrio species antibiotics resistance requires new treatments and prevention tools to be developed.
Probiotics can generally be defined as live microorganisms that provide animals with beneficial effects against harmful microbes and are a possible preventative treatment in the hatchery setting. Phaeobacter inhibens S4 (S4) has been isolated, characterized, and developed as a commercial formulation of probiont for the prevention of vibriosis in oyster shellfish hatcheries. Similar to other P. inhibens isolates, S4 can produce a secondary metabolite, tropodithietic acid (TDA), which has antimicrobial activity and regulates biofilm formation, as does the quorum-sensing signaling molecule N-acyl-homoserine lactone (AHL). Probiont S4 shows antimicrobial activity against several pathogens of larval bivalves, including Vibrio coralliilyticus RE22, which causes high mortality rates in molluscan shellfish hatcheries, and Aliiroseovarius crassostreae, the causative agent of Juvenile (or Roseovarius) Oyster Disease. According to extensive evaluation of the efficacy of probiont S4 treatment in hatcheries, there is, however, a large variation on the effects of treatment on larval performance and the microbial ecology within tanks within and between trials. Thus, this study seeks to investigate bacteriophages (viruses of bacteria) as a factor in the variability of probiotic efficacy in the hatchery.
Chapter I revealed that Phaeobacter inhibens strain S4Sm had up to nine possible prophage regions. Three of these regions contained an acyl homoserine lactone (AHL) biosynthetic cluster, and two of these AHL regions showed similarity to other Phaeobacter species, indicating evolutionary conservation or a horizontal transfer event. Many prophages were identified to be unique to S4, but one common prophage was discovered to be similar to those in other genera within the Roseobacter. When competing of S4 with pathogen Vibrio coralliilyticus, several prophage genes showed they were transcriptionally regulated which identifies functionality under host threat.
Chapter II isolated JASPR, a newly identified vibriophage against V. coralliilyticus RE22, from seawater containing hard clams recovered from Rhode Island, USA. JASPR was found to be highly specific to strain RE22 and showed no evidence of lysing several Vibrio coralliilyticus, Vibrio neptunius and Vibrio mediterranei strains. JASPR was also efficient at reducing RE22 growth and lacked any virulence or antibiotic-resistant genes. Ultimately, the study characterizes that JASPR has applications as a potential therapeutic treatment for larval shellfish hatcheries.
For the final test in Chapter III, bacteriophages were investigated as a tool for preventing vibriosis in eastern oyster larvae. Vibrio phages JASPR and vB_VcorM-GR23A were tested for their ability to infect and lyse the pathogen Vibrio coralliilyticus RE22 and the probiont Phaeobacter inhibens S4. Despite JASPR's inability to lyse S4, JASPR elicited morphological changes within S4Sm, resulting in elongated cells. Vibrio phages JASPR and 23A significantly protected larvae to challenge with pathogen V. coralliilyticus RE22. Levels of protection provided by phages were higher than those provided by probiont S4.
Recommended Citation
Andrews, Jamal Shinya, "EFFECT OF BACTERIOPHAGES ON PATHOGEN-PROBIOTIC INTERACTIONS IN BIVALVE AQUACULTURE SYSTEMS" (2026). Open Access Dissertations. Paper 4581.
https://digitalcommons.uri.edu/oa_diss/4581