Anjali Bhatnagar
Ph.D. Candidate, USC MEB
Spatiotemporal variation in the Trichodesmium microbiome
Abstract: Trichodesmium is an important nitrogen (N) fixing cyanobacterium found in the nutrient-limited, oligotrophic tropical and subtropical oceans where it can contribute up to 50% of the new N, driving primary productivity. In the ocean, Trichodesmium filaments often aggregate into colonies that host a diverse consortium of microbes that can influence their physiology. These associations are thought to be selective, as these phytoplankton-associated microbial communities are often comprised of members of similar lifestyles and are distinct from the communities of the surrounding seawater. Emerging research suggests that phytoplankton genotype may play a role in structuring these communities. While Trichodesmium supports a diverse microbiome, it is unclear what factors may shape the community structure. Using high depth metagenomes of Trichodesmium colonies collected across the subtropical and tropical Atlantic Ocean, we examined how Trichodesmium species abundances shape epibiont community composition. Previously assembled heterotrophic metagenome-assembled-genomes (MAGs) from Trichodesmium colonies and genes specific to species from the two major Trichodesmium clades were read mapped against Trichodesmium metagenomes from the North Atlantic, North Pacific and Red Sea. Trichodesmium community composition differs by ocean region, and we see a corresponding change in the epibiont community composition. Our results suggest that Trichodesmium genotype may enrich for specific heterotrophs.
Yiwei Shang
Ph.D. Candidate, USC MEB
Distribution and Ecological Role of B Vitamins in
Regulating Microbial Dynamics Across the Atlantic Ocean
Abstract: B vitamins are essential organic cofactors for microbial metabolism, driving the proliferation of most marine phytoplankton and bacteria through complex nutritional interdependencies. These vitamins, produced by prototrophic microbes and required by auxotrophic counterparts, assist enzymes in critical metabolic processes, including carbon fixation, nitrogen fixation, and DNA synthesis. However, the role of specific B vitamins and their vitamers in regulating phytoplankton dynamics remains poorly understood, with environmental measurements in the ocean still very limited. Here, we present direct quantifications of thiamins (vitamin B1), cobalamins (vitamin B12), and their chemically related metabolites, across the tropical and subtropical Atlantic Ocean, using liquid chromatography-mass spectrometry (LC-MS) after solid-phase extraction for preconcentration. These vitamins were detected at femto- to pico-molar concentrations in the dissolved pools. We found a strong inverse linear relationship between one of the active (Ado-B12) and storage (CN-B12) forms of cobalamin across all three Atlantic transects, suggesting the potential exchange of this metabolite within the water column. Furthermore, correlations between selected B vitamins and phytoplankton biomass reveal the ecological significance of these micronutrients. Our findings provide evidence of trace-level B vitamins in mediating microbial interactions across expansive regions of the open ocean.
Tuesday, February 25
11:30 AM
AHF 153 (Torrey Webb Room)