Variations in the bacterial and fungal community structure along the hypoxic gradient of the Arabian Sea oxygen-depleted environment based on eDNA metabarcoding analysis

Abstract The Arabian Sea hosts one of the major perennial, oceanic oxygen-depleted environments (ODE) in the water column, influencing the seabed beneath it. These regions harbor a vast diversity of microbial communities, which play a significant role in the global budgets of key biogenic elements like carbon, nitrogen and oxygen. This study assessed the relative importance of bacterial and fungal communities in the Arabian Sea ODE using eDNA metabarcoding tools. Sediment samples from four stations at ∼200–1,200 m depths were analyzed across a hypoxic gradient, with 5–35 μM dissolved oxygen levels. Species diversity and richness indices revealed that bacterial and fungal communities were the highest at an oxygen threshold of 10–20 μM, with variations in their community composition along the hypoxic gradient. The bacterial phylum Proteobacteria was dominant in the sediment of all stations. However, the relative abundances of phyla such as Firmicutes, Chloroflexi, Bacteroidetes, Planctomycetes and Actinobacteria varied across the stations. The phyla Ascomycota and Basidiomycota dominated the fungal communities at all the stations. However, Mucoromycota was present only at stations with 20–35 μM oxygen levels. These results enhance our understanding of microbial community distribution in the Arabian Sea ODE.