Effects of dam building on Niche differentiation of Comammox Nitrospira in the main stream of the Three Gorges Reservoir area

Comammox Nitrospira can completely oxidize ammonia nitrogen to nitrate, and the various habitats of comammox Nitrospira are an important guarantee for its survival. This study investigated comammox in river sediments in the Three Gorges Reservoir area. Comammox clade A and comammox clade B were detected in all samples, in which comammox clade A was dominant, and the OUTs detected from comammox clade B (14 OTUs) were more than those detected from comammox clade A. 1 (11 OTUs) and comammox clade A.2 (4 OTUs). The abundance of comammox Nitrospira clade A and clade B amoA genes in the main stream of the Three Gorges Reservoir indicated an increasing trend along the river stream, and reached the maximum in the of the reservoir area. The highest abundance of AOA amoA genes appeared in the upper stream section of the reservoir area. Comammox Nitrospira clade A exhibited the highest abundance (3.00×10 4 ±8782.37 copies/g), followed by comammox Nitrospira clade B (1.83×10 3 ±1019.82 copies/g), AOB (1.28×10 3 ±574.69 copies/g), AOA (1.73 ×10 2 ±48.05 copies/g). Both the abundances of comammox clade A and B were positively correlated with sediment pH, indicating that pH was an important environmental factor affecting the growth of comammox bacteria. The Mantel test chart indicated that overlying water dissolved oxygen (DO) in the reservoir area had a significant effect on the differentiation of comammox clade A into comammox clade A.1 and comammox clade A.2. This study confirms that the construction of the Three Gorges Dam has an impact on the niche differentiation of comammox Nitrospira in the main stream of the Three Gorges Reservoir area.