The anammox activity of a freshwater anammox consortium was strongly inhibited at low-salinity level. Stepwise adaptation from 0 to 3 g NaCl L took 153 days. Further adaptation to high-salinity concentration (from 3 to 30 g L) took only 40 days, and no inhibition was observed. A comprehensive insight into the salinity-induced successions of the total and the anammox communities was obtained by 454 pyrosequencing of 16S rRNA gene amplicons and statistical analysis. A major succession in the anammox community was observed at 3 g L where the dominating population shifted from Candidatus Brocadia fulgida to Ca. Kuenenia stuttgartiensis. The latter dominated at high salinity and seemed to be essential for the high (˃96%) ammonium and nitrite removal efficiencies achieved. SIMPER analysis indicated that these two dominating anammox species explained most to the differences in community structure among samples and helped in identifying other important members at different salinities.
In this study, nitrification before and after abrupt cross-transfer in salinity was investigated in two moving bed biofilm reactors inoculated with nitrifying cultures that had adaptation to freshwater (FR) and seawater salinities (SR). FR and SR MBRRs were exposed to short and long term cross-transfer in salinity, and the functional capacity of nitrifying microbial communities was quantified by the estimation of ammonia and nitrite oxidation rates. Salinity induced successions were evaluated before and after salinity change by deep sequencing of 16S rRNA gene amplicons and statistical analysis. The bacterial community structure was characterized and Venn diagrams were included. The results indicated that after salinity cross-transfer, the FR was not significantly recovered at seawater salinity whereas SR showed high resistance to stress caused by low-salt. Succession and physiological plasticity were the main mechanisms of the long-term adaption of the nitrifying communities exposed to abrupt salinity changes. Independently of salinity, some nitrifiers presented high physiological plasticity towards salinity and were very successful at both zero and full seawater salinity. SR culture is robust and suitable inoculum for ammonium removal from recirculating aquaculture systems and industrial wastewaters with variable and fast salinity changes. Our findings contradict the current perspective of the significance of salinity on the structure of nitrifying communities.
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