The significant contribution of comammox bacteria to nitrification in a constructed wetland revealed by DNA-based stable isotope probing

The discovery of Comammox bacteria (CMX) has changed our traditional concept towards nitrification, yet its role in constructed wetlands (CWs) remains unclear. This study investigated the contributions of CMX and two canonical ammonia -oxidizing microorganisms, ammonia -oxidizing bacteria (AOB) and archaea to nitrification in four regions (sediment, shoreside, adjacent soil, and water) of a typical CW using DNA -based stable isotope probing. The results revealed that CMX not only widely occurred in sediment and shoreside zones with high abundance (5.08 x 10 4 and 6.57 x 10 4 copies g -1 soil, respectively), but also actively participated in ammonia oxidation, achieving ammonia oxidation rates of 1.43 and 2.00 times that of AOB in sediment and shoreside, respectively. Phylogenetic analysis indicated that N. nitrosa was the dominant and active CMX species. These findings uncovered the crucial role of CMX in nitrification of sediment and shoreside, providing a new insight into nitrogen cycle of constructed wetlands.