Nitrous oxide (N2O; laughing gas) is a potent greenhouse gas and one of the main causes of ozone layer depletion [1]. Over the last century, human activities have greatly increased N2O emissions, mainly from agriculture, livestock farming and wastewater treatment. N2O is produced by nitrifiers, denitrifiers and microorganisms that catalyse dissimilatory nitrate/nitrite reduction to ammonia (DNRA) [1-3]. However, only one type of nitrous oxide reductase (NosZ) has been described. This enzyme is found in bacterial and archaeal species from several phyla, including Proteobacteria and Firmicutes [2]. Many of these organisms are able to grow by N2O respiration.

Several N2O-reducing strains of the genera Pseudomonas, Alcaligenes and Comamonas were recently isolated from an anaerobic digester and a wastewater treatment plant. Here, the effects of temperature and oxygen availability on these cells were investigated. Growth curves were determined in the range of 15 °C to 37 °C using an acetate-based medium and supplying an atmosphere of pure N2O. Microrespirometry was used to measure specific N2O reduction rates. In all isolates, the presence of oxygen either inhibited or abolished N2O reduction. However, upon oxygen depletion, nitrous oxide reduction rapidly resumed, albeit at a slightly reduced rate. Hypotheses to explain this phenotype at the molecular level will be discussed.

References

1 Stein LY (2020). The long-term relationship between microbial metabolism and greenhouse gases. Trends Microbiol. 28, 500–511

2 Torres MJ, Simon J, Rowley G, Bedmar EJ, Richardson DJ, Gates AJ & Delgado MJ (2016). Nitrous oxide metabolism in nitrate-reducing bacteria: physiology and regulatory mechanisms. Adv. Microb. Physiol 68, 353–432

3 Hein S & Simon J (2019) Bacterial nitrous oxide respiration: electron transport chains and copper transfer reactions. Adv. Microb. Physiol. 75, 137–175