题目:   Insights into prokaryotic community and its potential functions in nitrogen metabolism in the Bay of Bengal, a pronounced oxygen minimum zone

作者:  Bowei Gu, Jiaxing Liu, Shunyan Cheung, Ngai Hei Ernest Ho, Yehui Tan, Xiaomin Xia

刊物: Microbiology Spectrum

年卷期页: 2022, 118565

摘要：Ocean oxygen minimum zones (OMZs) around the global ocean are expanding both horizontally and vertically. Multiple studies have identified the significant influence of anoxic conditions (≤1?μM O2) on marine prokaryotic communities and biogeochemical cycling of elements. However, little attention has been paid to the expanding low-oxygen zones where the oxygen level is still above the anoxic level. Here, we studied the abundance and taxonomic and functional profiles of prokaryotic communities in the Bay of Bengal (BoB), where the oxygen concentration is barely above suboxic level (5?μM O2). We found the sinking of Trichodesmium into deep water was far more efficient than that of Prochlorococcus, suggesting Trichodesmium blooms might be an essential carbon and nitrogen source for the maintenance of the BoB OMZ. In addition to the shift in the prokaryotic community composition, the abundance of some functional genes also changed with the change of oxygen concentration. Compared to oxic (>60?μM O2) Tara Ocean and high-hypoxic (>20 to ≤60?μM O2) BoB samples, we found more SAR11-nar sequences (responsible for reducing nitrate to nitrite) in low-hypoxic (>5 to ≤20?μM O2) BoB waters. This suggested SAR11-nar genes would be more widespread due to the expansion of OMZs. It seems that the nitrite-N was not further reduced to nitrogen through denitrification but likely oxidized to nitrate by Nitrospinae in the BoB OMZ and then accumulated in the form of nitrate-N. However, the lack of N2 production in the BoB would change if the BoB OMZ became anoxic. Together, these results suggested that reduction of oxygen concentration and OMZ expansion may increase the use of nitrate by SAR11 and N2 production in the BoB.