Viruses in mangrove-cordgrass estuary sediments have a broad genetic repertoire for carbon cycling. Estuarine Metagenome-Assembled Genomes

Coastal ecosystems are among the most productive on the planet. Sediment microbes, and their associated viruses, in estuaries are major players in global carbon and nutrient cycles. However, due to the complexity of these communities, we are just beginning to explore the diversity and functional capacity of these communities. Here, we employed metagenomic sequencing of mangrove-cordgrass estuary sediments in winter/summer, day/night, as well as distinct environments (mangrove and seagrasses). From this we reconstructed 496 metagenomic-assembled genomes (MAGs) and 912 dsDNA uncultivated viral genomes (UViGs). This revealed a core set of microbial taxa that, constrained by depth in the sediments, are capable of organic carbon processing and nutrient cycling including sulfur oxidation, anammox, and nitrite reduction. Viruses (mainly related to Caudovirales) in the ecosystem have a variety of genes predicted to be involved in carbon utilization including simple sugars, carbohydrates, chitin, and sulfur assimilation. This study offers a first glimpse into virally-mediated biogeochemical dynamics in estuaries that are undergoing rapid vegetation shifts.