Spatiotemporal conservation of bacteria in the Trichodesmium microbiome

Trichodesmium is a major nitrogen fixer in the nutrient-limited tropical and subtropical ocean, contributing up to 50% of new nitrogen and driving primary productivity. Trichodesmium filaments often aggregate into colonies that host a diverse consortium of microbes that can influence their activity and physiology; however, it is unclear what factors shape community structure. To address this, we used metagenomics of Trichodesmium colonies collected across the subtropical and tropical Atlantic Ocean to examine how Trichodesmium diversity and abundance shape epibiont community composition. Heterotrophic metagenome-assembled-genomes from Trichodesmium colonies and genes specific to the major Trichodesmium subclades were read mapped against Trichodesmium metagenomes from the North Atlantic, the Western Tropical South Pacific, and the Red Sea. Using this global survey of Trichodesmium subclade distribution patterns and their enriched heterotrophs, we found unique core microbiomes that are specific to Trichodesmium subclades across ocean basins. Genome characteristics of the enriched heterotrophs reveal a genomically small, slow-growing community consistently associates with colonies. Our results suggest that Trichodesmium genotype may influence epibiont community structure, indicating a role for deterministic processes in shaping the microbiome.