Date of Award

2019

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Department

Fisheries, Animal and Veterinary Science

First Advisor

Marta Gomez-Chiarri

Abstract

Bivalve hatcheries include microalgae culture operations as a food source for stock, and these algae cultures harbor dynamic bacterial communities. Because algae from these cultures and their commensal microbiota are distributed to stock larval tanks daily upon feeding, the presence of pathogenic Vibrio spp. in hatchery microalgae cultures is a threat to stock health and survival. This study investigates the algal/bacterial and bacterial/bacterial interaction between four popular species of microalgae feedstock, a Vibrio sp. of known pathogenicity to bivalves (V. coralliilyticus RE22 [RE22]), a probiotic marine bacterium with demonstrated effectiveness in reducing larval shellfish mortality in culture operations (Phaeobacter inhibens S4 [S4]), and bacteria strains isolated directly from these algal cultures. Algal growth was unaffected by the addition of probiotics and/or RE22. Results showed that RE22 and S4 have different abilities to grow and persist in coculture, and that the four microalgae species studied have species specific effects on the levels of RE22 and S4. For example, S4 titers were unaffected by coculture with the microalga Pavlova pinguis, yet significantly decreased more than 3- log10 when cocultured with Tisochrysis lutea. An antibiotic knockdown experiment and a zone of inhibition assay with commensal isolates suggest that RE22 and S4 do interact with commensal bacteria. Probiotics cocultured with algae and RE22 did not increase the effect of the algae on RE22 levels, and probiotics did not reach high enough levels in coculture to contribute to stock health via routine algae feeding protocols. For these reasons, benefits of supplementing probiotic to microalgal cultures cannot be claimed without further research and development. This research enhances our understanding of algal/bacterial interaction in shellfish hatcheries and informs methods of probiotic delivery to larvae in bivalve hatcheries.

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