Denitrifying haloarchaea: sources and sinks of nitrogenous gases

Haloarchaea thrive under saline and hypersaline conditions and often dominate microbial communities in saltmarshes, salted lakes/soils and some oceanic areas. Some of the predominant species show denitrifying capabilities, although it remains unclear whether they are complete or partial denitrifiers. As complete denitrifiers, they could play important roles buffering ecosystems in which nitrate and nitrite appear as contaminants. However, partial denitrifying haloarchaea could contribute to the emission of nitrogenous gasses, thus acting as drivers of climate change and ozone depletion. In this review, we summarise some recent results on denitrification in haloarchaea, discuss the environmental implications and outline possible applications in mitigation. Finally, we list questions to be addressed in the near future, facilitating increased understanding of the role of these organisms in N turnover in arid and hypersaline environments.