The role of microbial communities within the Arabian Sea oxygen minimum zones (AS-OMZ), is critical for understanding the microbes-mediated biogeochemical and climatic processes. Here, we perform comparative analysis of structure and diversity of bacterial communities within the OMZ depths and non OMZ (NOMZ) depths of the Arabian Sea and Central Indian Ocean basin (CIOB) respectively, using v3-v6 region of the 16S rRNA gene. Proteobacteria was the predominant phylum in both regions. Gammaproteobacteria was the major class and Alteromonadaceae was the primary family at the OMZ depths. Whereas Gamma- and Alphaproteobacteria were the dominant classes with Pelagibacteraceae as the major family in NOMZ depths. Significantly, sequences affiliated to Synechococcaceae were exclusively detected at 250 m within the OMZ depths across all seasons. Presence of isolates linked to Rhodospirillales, Phycisphaerales and Thiotrichales/Desulfobacterales indicate potential involvement in denitrification, anammox, and sulfur oxidation /reduction process respectively. Overall, bacterial diversity was greater in NOMZ depths, while higher number of OTUs were detected in OMZ depths. Within the OMZ, diversity indices and the number of OTUs revealed greater bacterial richness and diversity at 250 m compared to 500 m. Canonical correspondence analysis (CCA) highlighted dissolved oxygen (DO), silicate and nitrate as the primary factors contributing to the variability of the bacterial diversity at NOMZ site whereas salinity, ammonia and nitrite had more influence at OMZ sites. In conclusion, our study demonstrates distinct variation in bacterial diversity between anoxic/hypoxic vs oxygenated marine habitats with no observed temporal variation.
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