The dominance of non-halophilic archaea in autotrophic ammonia oxidation of activated sludge under salt stress: A DNA-based stable isotope probing study.

Dynamics of nitrification activity, ammonia-oxidizing archaea (AOA) and bacteria (AOB) abundance and active ammonia oxidizers of activated sludge were explored under different salinities. Results showed that specific ammonium oxidation rates were significantly negative with increasing salinity. The responses of AOA and AOB populations to salt stress were distinct. AOA abundance decreased at moderate salinities (2.5, 5 and 7 g L) and increased at high salinities (10, 15, 20 and 30 g L), while AOB abundance showed opposite tendency. DNA-based stable isotope probing assays indicated AOA exclusively dominated active ammonia oxidation of test samples under different salinities. The active AOA communities retrieved were all non-halophilic and regulated by salinities. Candidatus Nitrosocosmicus exaquare and Ca. Nitrosocosmicus franklandus were the predominantly active AOA in both salt-free and salt-containing microcosms, while C-labeled Nitrososphaera viennensis and Ca. Nitrososphaera gargensis were only retrieved from the microcosms amended with 0 and 30 g L salinity, respectively.