Activity, Abundance, and Community Composition of Anaerobic Ammonia–Oxidizing (Anammox) Bacteria in Sediment Cores of the Pearl River Estuary

Anaerobic ammonium oxidation (anammox) is an important pathway for the removal of fixed nitrogen from aquatic and terrestrial ecosystems. Previous studies on anammox were focused on the surface sediments in estuaries, but the activity and community composition of anammox bacteria in the estuarine subsurface sediments remained unknown. In this study, we used high-throughput sequencing of 16S rRNA gene combined with ¹⁵N isotope tracing method to investigate the activity, diversity, and spatio-temporal distribution of anammox bacteria in sediment cores of the Pearl River Estuary (PRE). Our results indicated that anammox in the subsurface sediments has significant potential activity, contributing to approximately 17.49% of the total microbial nitrogen loss. A variety of anammox bacteria, including Candidatus Scalindua, Ca. Brocadia, Ca. Jettenia, and Ca. Kuenenia, were all detected in the subsurface sediments. Moreover, the anammox bacterial community had a significant specific geographic distribution but no obvious difference along the sediment depth. Multiple environmental factors including salinity, and NH₄⁺ and NO₃⁻ contents, synergistically shaped the diversity and distribution of anammox bacteria in PRE sediments.