Greenhouse gas - nitrous oxide (N2O)- production by marine nitrifiers

一氧化二氮(N2O)是一种平流层臭氧消耗剂，也是一种强有力的温室气体，其全球变暖潜力是二氧化碳的300倍。全球约三分之一的N2O排放发生在海洋中。尽管它的产生在所谓的氧气最低限度内的缺氧水域特别强烈，但至少有一半发生在更广泛的含氧海洋中。海洋硝化菌由两组微生物组成，它们分别将氨氧化成亚硝酸盐，然后再氧化成硝酸盐，已知能够产生N2O。最值得注意的是，培养研究和自然稳定的N2O同位素特征表明，氨氧化古生菌是海洋N2O产生的主要原因[1]。然而，古生菌产生N2O的分子机制仍然知之甚少。尽管实验室研究对可能的途径提出了一些假设(例如[2])，但它们在环境中的重要性仍未得到证实，而且在缺氧和缺氧条件下是否采用相同的机制尚不清楚。与此同时，最近发现亚硝酸盐氧化菌亚硝酸球菌在全球海洋中普遍存在，它还能够产生N2O[3]。该项目旨在利用最先进的分子技术，结合活性测量，研究海洋硝化菌产生N2O的分子机制。

Nitrous oxide (N2O) is a stratospheric ozone-depleting agent and a potent greenhouse gas with a global warming potential 300 times that of CO2. Approximately 1/3 of global N2O emissions occur in the oceans. Although its production is particularly intense in oxygen-deficient waters within the so-called oxygen minimum zones, at least half occurs in the wider oxic ocean. Marine nitrifiers - comprising two groups of microorganisms that respectively mediate the oxidation of ammonia to nitrite and then to nitrate - are known to be capable of producing N2O. Most notably, culture studies and natural stable isotopic signatures of N2O have shown that ammonia-oxidising archaea are largely responsible for oceanic N2O production [1]. However, the molecular mechanisms of such archaeal N2O production remain poorly understood. Despite some postulations on possible pathways from laboratory studies (e.g. [2]), their importance remains unconfirmed in the environment, and whether the same mechanism is employed in both oxic and oxygen-deficient conditions is unknown. Meanwhile, the nitrite-oxidiser Nitrococcus has recently been found to be ubiquitous across global oceans and it is also able to produce N2O [3]. This project aims to employ state-of-the-art molecular techniques, combined with activity measurements, to investigate the molecular mechanisms dictating the production of N2O production by marine nitrifiers.