Evidence for a persistent microbial seed bank throughout the global ocean

Do bacterial taxa demonstrate clear endemism, like macroorganisms, or can one site's bacterial community recapture the total phylogenetic diversity of the world's oceans? Here we compare a deep bacterial community characterization from one site in the English Channel (L4-DeepSeq) with 356 datasets from the International Census ofMarine Microbes (ICoMM) taken fromaround the globe (ranging frommarine pelagic and sediment samples to sponge-associated environments). At the L4-DeepSeq site, increasing sequencing depth uncovers greater phylogenetic overlap with the global ICoMMdata. This site contained 31.7-66.2% of operational taxonomic units identified in a given ICoMM biome. Extrapolation of this overlap suggests that 1.93 × 10¹¹ sequences from the L4 site would capture all ICoMM bacterial phylogenetic diversity. Current technology trends suggest this limit may be attainable within 3 y. These results strongly suggest the marine biosphere maintains a previously undetected, persistent microbial seed bank.