A comparison of bacterial communities from OMZ sediments in the Arabian Sea and the Bay of Bengal reveals major differences in nitrogen turnover and carbon recycling potential

Abstract

Abstract. The Northern Indian Ocean hosts two Oxygen Minimum Zones (OMZ), one in the Arabian Sea and the other in the Bay of Bengal. High-throughput sequencing was used to understand the total bacterial diversity in, the surface sediment off Goa within the OMZ of the Arabian Sea, and from off Paradip within the OMZ of the Bay of Bengal. The dominant phyla identified included Firmicutes (33.08 %) and Proteobacteria (32.59 %) from the Arabian Sea, and Proteobacteria (52.65 %) and Planctomycetes (9.36 %) from the Bay of Bengal. Only 30 % of OTUs were shared between the sites which make up three-fourth of the Bay of Bengal OMZ bacterial community, but only one-fourth of the Arabian Sea OMZ sediment bacterial community. Statistical analysis indicated the bacterial diversity from sediments of the Bay of Bengal OMZ is ~ 48 % higher than the Arabian Sea OMZ. The community analysis combined with a predictive functional profiling of 16S rRNA amplicons pinpointed the occurrence of specific enzymes that are crucial in the cycling of nitrogen and sulfur compounds, with major differences regarding nitrogen fixation and carbon recycling.

Phylogenetic diversity of culturable marine bacteria from sediments underlying the oxygen minimum zone of the Arabian Sea and their role in nitrate reduction

“…Isolates from OMZ sediments common to all three sampling sites, that is, from off‐Goa, off‐Cochin, and off‐Mangalore regions belonged to genera Alteromonas , Salegentibacter , Gracilibacillus , and Bacillus sp. These genera are previously reported from OMZ region of Arabian Sea (Gomes et al., 2019; Lincy & Manohar, 2020; Paingankar et al., 2020) except Gracilibacillus sp., as per our knowledge, not reported in OMZ region of Arabian Sea. Alteromonas sp.…”

“…Previous study on OMZ sediments carried out in deep benthic eastern AS‐OMZby using metagenomic approach has reported a Shannon diversity ( H ) index of 4.4 (Divya et al., 2011), and in South and East China Sea sediment samples, H index is 2.52 and 7.96, respectively (Dang et al., 2008; Zhu et al., 2013). Recent bacterial diversity sediment studies using pyrosequencing method by Lincy and Manohar (2020) has reported a H index of 4.37 and 6.97 for OMZs of Arabian Sea and Bay of Bengal, respectively, while In our study, H index was highest at off‐Cochin, that is, 2.46. Simpson diversity index ranges between 0 and 1, the greater the value, the greater the diversity; the highest diversity was seen in off‐Cochin (0.95), while lowest at off‐Goa (0.79), thus confirming that the microbial population at off‐Cochin is highly diverse.…”

“…Simpson diversity index ranges between 0 and 1, the greater the value, the greater the diversity; the highest diversity was seen in off‐Cochin (0.95), while lowest at off‐Goa (0.79), thus confirming that the microbial population at off‐Cochin is highly diverse. Simpson diversity index was reported as 0.934 at Arabian Sea station (GS1) and 0.998 at Bay of Bengal station (PS1B), respectively, by Lincy and Manohar (2020).…”

“…The presence of gram‐positive bacteria in marine environment is reported in previous study (Da Silva et al., 2013; Gontang et al., 2007; Sass et al., 2008; Zhuang et al., 2003), and in several cases, these microorganisms are dominant among the cultivable bacteria (Gärtner et al., 2011; Toffin et al., 2004; Velmurugan et al., 2011). Recently, while studying bacterial communities from OMZ of the northern Indian Ocean, Lincy and Manohar (2020) reported Firmicutes sp. as dominant phyla underlying the OMZ sediments.…”

Vertical Microbial Profiling of Arabian Sea Oxygen Minimal Zone Reveals Complex Bacterial Communities and Distinct Functional Implications

“…The results obtained in this study corroborate with earlier observations on active sulphur cycle in marine sediments. The presences of members from Planctomycetes group that are involved in anammox reaction in OMZ sediments are consistent with similar studies in Arabian Sea and Bay of Bengal [55]. The OMZ sediments were also replete with methanotrophs including significant representation from the NC10 phylum member methylomirabilis, indicating their strong role in methane oxidation coupled with nitrite reduction.…”