Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.
University of Chinese Academy of Sciences, Beijing, China.
Microbiol Spectr. 2022 Jun 29;10(3):e0089221. doi: 10.1128/spectrum.00892-21. Epub 2022 May 17.
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 O) 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 O). We found the sinking of into deep water was far more efficient than that of , suggesting 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 O) Tara Ocean and high-hypoxic (>20 to ≤60 μM O) BoB samples, we found more SAR11- sequences (responsible for reducing nitrate to nitrite) in low-hypoxic (>5 to ≤20 μM O) BoB waters. This suggested SAR11- 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 in the BoB OMZ and then accumulated in the form of nitrate-N. However, the lack of N 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 N production in the BoB. Recognizing the prokaryotic community and its functions in hypoxic (>5 to ≤60 μM O) environments before further expansion of OMZs is critical. We demonstrate the prokaryotic community and its potential functions in nitrogen metabolism in the Bay of Bengal (BoB), where oxygen concentration is barely above suboxic level. This study highlighted that might be an essential carbon and nitrogen source in the maintenance of the BoB OMZ. Additionally, we suggest that the lack of N production in the BoB would change if the BoB OMZ became anoxic, and the expansion of OMZs in the global ocean may potentially increase the use of nitrate by SAR11.
全球海洋的海洋缺氧区（OMZ）正在水平和垂直方向上扩张。多项研究已经确定了缺氧条件（≤1μM O）对海洋原核生物群落和元素生物地球化学循环的重大影响。然而，对于氧气水平仍高于缺氧水平的扩张低氧区，人们关注甚少。在这里，我们研究了孟加拉湾（BoB）原核生物群落的丰度、分类和功能特征，该地区的氧气浓度勉强高于亚缺氧水平（5μM O）。我们发现下沉到深水中的效率远远高于，这表明可能是维持 BoB OMZ 的重要碳氮源。除了原核生物群落组成的变化外，一些功能基因的丰度也随着氧气浓度的变化而变化。与含氧（>60μM O）的 Tara 海洋和高缺氧（>20 至≤60μM O）的 BoB 样本相比，我们在低缺氧（>5 至≤20μM O）的 BoB 水中发现了更多的 SAR11-序列（负责将硝酸盐还原为亚硝酸盐）。这表明由于 OMZ 的扩张，SAR11-基因会更加广泛。似乎亚硝酸盐-N 没有通过反硝化进一步还原为氮气，而是很可能在 BoB OMZ 中被氧化为硝酸盐，然后以硝酸盐-N 的形式积累。然而，如果 BoB OMZ 变得缺氧，BoB 中的硝态氮产量将发生变化。总之，这些结果表明，氧气浓度的降低和 OMZ 的扩张可能会增加 SAR11 对硝酸盐的利用和 BoB 中的氮素产生。在 OMZ 进一步扩张之前，认识到缺氧（>5 至≤60μM O）环境中原核生物群落及其功能至关重要。我们展示了孟加拉湾（BoB）原核生物群落及其在氮代谢中的潜在功能，该地区的氧气浓度勉强高于亚缺氧水平。这项研究强调，可能是维持 BoB OMZ 的重要碳氮源。此外，如果 BoB OMZ 变得缺氧，BoB 中的硝态氮产量将发生变化，全球海洋 OMZ 的扩张可能会增加 SAR11 对硝酸盐的利用。
