Comammox Nitrospira clade A recovers faster than clade B after cyanobacteria outbreak in the Three Gorges tributary, China

Purpose Comammox Nitrospira can complete nitrification independently, and they are important participants in the nitrogen cycle. In this study, we investigated the comammox Nitrospira in the sediments of Xiaojiang River basin, a tributary of the Three Gorges, and explored the differences in the responses of its different clades to water quality recovery during a cyanobacteria outbreak period and a water quality recovery period. Materials and methods Sediment samples were taken from the two water quality periods of the Yangtze River tributary Xiaojiang, namely, the cyanobacteria outbreak period and the water quality recovery period. The diversity of comammox Nitrospira clade A and comammox Nitrospira clade B, and the abundance of comammox Nitrospira clade A, comammox Nitrospira clade B, ammonia-oxidizing archaea (AOA), and ammonia-oxidizing bacteria (AOB) were measured. Results and discussion The results showed that during the water quality recovery period, the abundance of both comammox clade A amoA (4.32 × 10 6 ± 1.32 × 10 6 copies g −1 ) and comammox clade B amoA (4.06 × 10 6 ± 2.91 × 10 6 copies g −1 ) exhibited an increasing trend. Compared with that in the cyanobacteria outbreak period, the abundance of comammox clade A was increased by 450% during the water quality recovery period, while comammox clade B was increased by 195%. During the water quality recovery period, both comammox Nitrospira species richness (Chao1) and species diversity (Pielou, Shannon, and Simpson) were increased. Conclusions During the water quality recovery period, comammox clade A amoA exhibited a greater increase in abundance and a quicker response to water quality recovery than comammox clade B. Water quality recovery favored the growth of comammox Nitrospira .