Shore-to-water spatial variations of complete ammonia oxidizers in a lake in Wuhan, China

Complete ammonia oxidizers (comammox bacteria) can convert ammonia into nitric acid through single-step nitrification. This study explored the spatial variations of comammox bacteria in the lakeshore area of the Houguan Lake in Wuhan, China. The abundance of the two comammox bacteria clades and two traditional ammonia-oxidizing microorganisms, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), generally showed a gradually decreasing trend from the shore to the water. Moreover, a similar decreasing trend was observed for the respective and total nitrification rate of three types of ammonia-oxidizing microorganisms. The average nitrification rate of AOA, AOB and comammox bacteria was 0.568, 0.718, and 0.935 mg N kg⁻¹ d⁻¹, respectively. Besides, comammox bacteria exhibited a high biological diversity, with clade A and clade B and three subclades of clade A all present. Among different clades, clade B played a dominant role in the ammonia oxidation process. Both the abundance and nitrification rate of comammox bacteria were significantly positively correlated with total carbon and total nitrogen, indicating that these two nutrient substances are important factors influencing this microorganism. Our results demonstrate that the spatial variations of environmental elements in the lakeshore area lead to gradual decreases of comammox bacteria from the shore to the water.