High prokaryotic diversity in the oxygen minimum zone of the Bay of Bengal: Implications for nutrient cycling

The Bay of Bengal hosts the fourth most intense oxygen minimum zone (OMZ) globally, despite low primary productivity. Yet its microbial community and biogeochemical roles remain underexplored. We examined prokaryotic diversity in the euphotic zone and OMZ, revealing significantly higher alpha diversity in the OMZ than surface waters. Community structures varied between coastal and open ocean regions and within the OMZ across oxygen gradients. Proteobacteria dominated bacterial communities, with Cyanobacteria and Actinobacteria prevalent in the euphotic zone. In contrast, Marinimicrobiota, Marine Group B, Crenarchaeota, and others dominated the OMZ. Key genera included Prochlorococcus and SAR11 in the euphotic zone and SUP05 and SAR324 in the OMZ. Functional predictions indicated the prominence of denitrifiers, anammox bacteria, and sulfur oxidizers in the OMZ. This study underscores the critical role of microbial diversity in nitrogen and sulfur cycling in the Bay of Bengal.