Biodiversity And Abundance Of Comammox Bacteria In Sediments Of Lake Donghu And Lake Tangxun In Wuhan

The complete ammonia oxidizers?comammox?bacteria can oxidize ammonia to nitrate directly,and their discovery has changed the long-term understanding of nitrification that ammonia needs to be oxidized to nitrate in two steps.Comammox bacteria have been found in a variety of ecosystems,but there are few studies in urban lakes.In this study,the sediments of two typical urban lakes,Lake Donghu and Lake Tangxun in Wuhan,were selected as the research objects.The diversity of comammox bacteria and the abundance of ammonia-oxidizing bacteria?AOB?,ammonia-oxidizing archaea?AOA?,comammox bacteria,and anaerobic ammonia-oxidizing?anammox?bacteria in sediments were studied by molecular ecology methods,such as DNA extraction,PCR amplification,and clone sequencing,in order to understand the ecological relationship between comammox bacteria and other ammonia-oxidizing microorganisms.The main results are as follows:?1?Comammox bacteria could exist in urban eutrophication lakes.Comammox bacteria in the sediments of Lake Donghu and Lake Tangxun belong to comammox clade A,and Nitrospira nitrosa cluster dominateed in the sediments of Lake Donghu,while Nitrospira nitrosa cluster and Nitrospira inopinata cluster dominated in the sediments of Lake Tangxun,indicating that these two species may play an important role in the process of ammonia-oxidation in the lake.?2?Comammox bacteria,AOA,AOB,and anammox bacteria can co-exist in the sediments of Lake Donghu and Lake Tangxun.The average amo A gene abundance of comammox bacteria,AOA,AOB,and anammox 16S r RNA gene abundance in the Lake Donghu sediments was 2.43×10⁸,1.07×10⁸,3.24×10⁷,3.21×10¹¹ copies·g^-1 dry sediment.The average abundance of comammox bacteria,AOA,AOB amo A gene,and anammox16S r RNA gene in the sediment of Lake Tangxun was 9.57×10⁷,3.51×10⁷,2.48×107,2.71×10¹¹ copies·g^-1 dry sediment.The abundance of comammox bacteria in the sediments of Lake Donghu and Lake Tangxun was higher than that of AOA and AOB,indicating that comammox bacteria may be dominant in the ammonia oxidation process of lake ecosystem.?3?In the five sub-lakes of Lake Donghu,the abundance of comammox bacteria showed the difference.The worse the water quality,the lower the abundance of comammox bacteria.Therefore,the intensification of lake eutrophication may inhibit the growth of comammox bacteria.In Lake Tangxun,the abundance of the comammox amo A gene was lower in the two sewage discharge areas(1.3×10⁷ copies·g^-1 dry sediment)than in the emergent plant areas(1.75×10⁸ copies·g^-1 dry sediment)and the bare sediment area(1.0×10⁸ copies·g^-1 dry sediment),indicating that sewage discharge also inhibited the growth of comammox bacteria.?4?Redundancy analysis?RDA?showed that the abundance of comammox bacteria in Lake Donghu was positively correlated with the concentration of TN and OM in the sediments,and negatively correlated with the concentration of TP,DO,and TN in the overlying water and the concentration of NO₃^--N,TP,and NH₄⁺-N in the sediments.In Lake Tangxun,the abundance of comammox bacteria was positively correlated with the concentration of TN,OM,and NO₂^--N in the sediments,while negatively correlated with the concentration of COD,TP,and TN in the overlying water and the concentration of NO₃^--N,TP,NH₄⁺-N,and p H in the sediments.These results indicate that OM and TN in sediments can promote the growth of comammox bacteria.?5?The abundance of comammox bacteria was positively correlated with the abundance of AOA and AOB in Lake Donghu,but the correlation with the abundance of anammox bacteria was weak.In Lake Tangxun,the abundance of comammox bacteria was positively correlated with the abundance of AOA,AOB,and anammox bacteria.