Abstract Nitrate reduction plays a key role in the biogeochemical dynamics and microbial ecology of coastal upwelling systems. Seasonal upwelling in the eastern Arabian Sea entrains nitrate rich waters to the surface, the intense productivity that follows leads to oxygen depletion and then denitrification. Heterotrophic bacteria comprise diverse functional groups. Both aerobic and facultative anaerobic heterotrophic bacteria capable of nitrate reduction are important functional groups in the nitrogen cycle due to their ability to respire anaerobically using nitrogen oxides as electron acceptors, which are reduced to nitrous oxide and dinitrogen. However little is known from the coastal Arabian Sea on the types/species of culturable bacteria catalyzing this crucial step. To recognize the species composition of the culturable fractions involved in nitrate reduction and nitrous oxide production, as many as 360 cultures of native heterotrophic bacteria were isolated and screened for nitrate reduction. Isolates were identified by sequencing their 16S rRNA gene and the rate of nitrate reduction and production of nitrous oxide by representatives of 30 different species of bacteria were measured. Close to 77% (or 277 of 360) of the cultures were found to be nitrate reducers, which grouped into 30 different species. Further, the nitrate reduction rates and nitrous oxide production by these 30 representative nitrate reducing species were measured. Cultures were capable of nitrate reduction up to 2.40 (×10−14) mol cell−1 and 5.54 (×10−15) mol cell−1 of nitrous oxide. This high fraction of culturable bacteria reducing nitrate and producing N2O in low oxygen conditions ought to reflect their important role in biogeochemical processes in the tropical coastal water experiencing hypoxia during SuM (Summer monsoon) and FIM (Fall intermonsoon) in the monsoon affected regions.

中文翻译：

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来自沿海地区的可培养细菌的反硝化率暂时缺氧

摘要 硝酸盐还原在沿海上升流系统的生物地球化学动力学和微生物生态学中起着关键作用。阿拉伯海东部的季节性上升流将富含硝酸盐的海水带到地表，随之而来的强烈生产力导致氧气耗尽，然后反硝化。异养细菌包含不同的官能团。能够还原硝酸盐的需氧和兼性厌氧异养细菌都是氮循环中的重要官能团，因为它们能够使用氮氧化物作为电子受体进行厌氧呼吸，将氮氧化物还原为一氧化二氮和二氮。然而，在阿拉伯海沿岸地区，人们对催化这一关键步骤的可培养细菌的类型/种类知之甚少。为了识别参与硝酸盐还原和一氧化二氮产生的可培养部分的物种组成，分离并筛选了多达 360 种天然异养细菌的培养物以进行硝酸盐还原。通过对它们的 16S rRNA 基因进行测序来鉴定分离株，并测量了 30 种不同种类细菌代表的硝酸盐还原率和一氧化二氮的产生率。发现接近 77%（或 360 个中的 277 个）的培养物是硝酸盐还原剂，分为 30 个不同的物种。此外，测量了这 30 种代表性的硝酸盐还原物质的硝酸盐还原率和一氧化二氮产生量。培养物能够将硝酸盐还原多达 2.40 (×10-14) mol cell-1 和 5.54 (×10-15) mol cell-1 的一氧化二氮。