A novel North Sea ammonia-oxidizing archaeon Nitrosarchaeum marinum leverages a high abundance of transport systems to grow over a wide salinity range

Ammonia-oxidizing archaea (AOA) are among the most abundant microorganisms in the biosphere. They are crucial for the global nitrogen cycle through catalyzing the oxidation of ammonia to nitrite. The biochemistry, physiology and mechanisms underlying the adaptation of AOA to diverse habitats are not fully understood, partly due to the lack of AOA pure laboratory cultures. In this study, we present the isolation of a novel species, Nitrosarchaeum marinum T12, the first Nitrosarchaeum strain isolated from a fully marine environment. We demonstrate that this AOA can grow over a vast salinity range (1-60 g L-1). Comparative genomics of Nitrosarchaeum and Nitrosopumilus strains revealed a highly diverse genetic repertoire, with many genes unique to single species. N. marinum T12 possesses genes for chemotaxis and motility and encodes 20 different transport systems potentially involved in osmoadaptation. This diversity of transporters might provide a key for flexibility and adaptation to growth over such a wide salinity range. Strain T12 may present an example of successful adaptation to increasing salt concentration, suggesting that these AOA might be, to a certain extent, resilient to future environmental changes.