Collaborative Research: Microbial Ecology of Nitrogen Cycling in the Oxygen Minimum Zone of the Arabian Sea

阿拉伯海虽然只占世界海洋面积的2%，但其发达的氧气最小区(OMZ)占水柱反硝化作用的20%，对海洋氮收支的贡献不成比例且显著。OMZ中原位反硝化活性的分布通常是通过指示化学变量之间的相关性来推断的，最重要的是硝酸盐亏缺、亚硝酸盐、氧气和悬浮颗粒物。氧、硝酸盐和有机碳的有效性调节反硝化细菌的潜力是众所周知的，并很容易在培养和沉积物环境中得到证明。在OMZ的水柱中，直接测量反硝化速率一直非常困难，因此，实际控制该环境中反硝化细菌活动的因素只能通过推理才能知道。最近认识到的厌氧氨氧化可能是反硝化信号的一部分(在固定氮的损失中)，这充分表明科学界对控制OMZ的N循环的因素缺乏预测性的了解。在这项研究中，普林斯顿大学和华盛顿大学的研究人员将调查OMZ细菌组合的群落结构，以评估多样性和生物地球化学之间的可能关系。科学家团队将分析编码反硝化关键酶(亚硝酸还原酶)的基因表达，以此作为反硝化活性的指标。基因丰度和表达数据将与常规用来推断反硝化速率的化学变量的分布进行比较，以研究反硝化活性的调节。除通常的化学指示剂外，还将涉及痕量金属形态，如铜的生物有效性，以调节反硝化细菌群落的组成和活性。以前的研究表明，反硝化细菌可以受到培养中铜的限制，并表明在OMZ中铜与硫化物的紧密络合将导致一氧化二氮的积累，这是在OMZ中观察到的特征。这一铜假说将通过比较添加和不添加铜的处理的反硝化率和基因表达来验证。就更广泛的影响而言，该项目显然将建立在一些主要海洋氮素专家之间强有力的国际合作的基础上。

ABSTRACTOCE- 0350720 / OCE- 0350683Although the Arabian Sea covers only 2 % of the area of the world ocean, it's well developed Oxygen Minimum Zone (OMZ) accounts for 20 % of the water column denitrification, a disproportionate and significant contribution to the marine nitrogen budget. The distribution of in situ denitrification activity in the OMZ is usually inferred from the correlation among indicator chemical variables, most importantly nitrate deficit, nitrite, oxygen, and suspended particulate material. The potential for oxygen, nitrate and organic carbon availability to regulate denitrifying bacteria is well known and easily demonstrated in culture and in sediment environments. Direct measurements of denitrification rates have been very difficult in the water column of the OMZ, and the factors that actually regulate the activity of denitrifying bacteria in this environment are therefore known only by inference. The recently recognized potential for anaerobic ammonia oxidation to account for part of the denitrification signal (in loss of fixed N) makes it abundantly clear that the scientific community lacks predictive understanding of factors controlling the N cycle of the OMZ. In this study, researchers at Princeton University and the University of Washington will investigate the community structure of the bacterial assemblage in the OMZ in order to evaluate the possible relationships between diversity and biogeochemistry. The team of scientists will assay gene expression for the gene that encodes the key enzyme in denitrification (nitrite reductase) as an indicator of denitrifying activity. Gene abundance and expression data will be compared with the distribution of the chemical variables that are used by convention to infer denitrification rates to investigate regulation of denitrifying activity. In addition to the usual chemical indicators, trace metal speciation such as copper bioavailability will be involved to regulate the denitrifying bacterial community composition and activity. Previous studies have demonstrated that denitrifying bacteria can be limited by copper in culture, and suggest that the tight complexation of copper with sulfides in the OMZ will lead to the accumulation of nitrous oxide that is characteristically observed in the OMZ. This copper hypothesis will be tested by comparing the denitrification rates and gene expression in treatments with and without copper additions. In terms of broader impacts, it is clear that this project that will build upon strong international collaboration among some of the premier marine nitrogen experts.