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

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.