<b>GRC Poster:</b> Identifying B-vitamin requirements and phycosphere interactions for the HAB-forming dinoflagellate, <i>Pyrodinium bahamense</i>

<p dir="ltr"><b>Abstract: </b><i>Pyrodinium bahamense, </i>a saxitoxin-producing dinoflagellate,<i> </i>forms harmful algal blooms in tropical and subtropical estuarine systems. In Florida, <i>P. bahamense</i> forms blooms in the Indian River Lagoon on the Atlantic coast and Old Tampa Bay on the Gulf coast, leading to shellfish closures and public health consequences across the state. To minimize impacts, it is necessary to forecast blooms accurately, but factors contributing to bloom timing and intensity remain poorly constrained. While many HAB-forming dinoflagellates are auxotrophic for one or more B-vitamins, <i>P. bahamanse’s</i> B-vitamin requirements have not been fully characterized. In this study, we test the effect of the B vitamins cobalamin, thiamine, and biotin on the growth of<i> P. bahamense</i>. We further test the ability of cocultured bacteria to provide the required B vitamins to <i>P. bahamense</i> and characterize the microbiome composition of both strains through metabarcoding. Our results show that <i>P. bahamense</i> is auxotrophic for cobalamin. The microbiomes associated with the two strains are distinct, which may be due to isolation and culturing methods. Results from this study provide a more complete understanding of the B-vitamin micronutrient requirements of <i>P. bahamense </i>and suggest that cobalamin availability could contribute to bloom formation. This improved understanding of <i>Pyrodinium </i>physiology and interactions with bacteria will equip stakeholders with additional information that could be leveraged to develop improved forecasting and mitigation tools. </p>