The diversity and distribution of anammox bacteria in the marine aquaculture zones.

The accumulation of toxic inorganic nitrogen is one of the major water quality problems in intensive aquaculture systems, thus the N removal in aquaculture systems is an important issue for the sustainable development of aquaculture. To understand one of the major microbial N removal processes, anaerobic ammonium oxidation (anammox), phylogenetic diversity, and distribution of anammox bacteria in sediments of four different marine aquaculture zones in Hong Kong (HK) were investigated. The 16S rRNA genes analysis indicated that sequences detected from Cheung Sha Wan (CSW) and Sok Kwu Wan (SKW) were closely related to several clusters within the Scalindua genus of anammox bacteria, including a new habitat-specific group, while only several sequences related to Scalindua and Kuenenia were detected in Sham Wan (SW) and Yim Tin Tsai East (YTTE). Most of the sequences obtained in SW and YTTE with the same PCR primers showed a low similarity to the known anammox bacteria, forming several novel groups within the Planctomycetes. However, results from the hydrazine oxidoreductase (HZO) encoding gene showed that only sequences from SW were related to the genus of Kuenenia, and sequences from other three sites were closely related to the genus of Scalindua. The community analysis showed that CSW and SKW share similar anammox bacterial community structures while SW and YTTE contain a unique anammox bacterial community. Furthermore, correlations reflect that organic matter is positively correlated with Kuenenia-like anammox bacteria, while the redox potential is significantly correlated with Scalindua-like anammox bacteria in marine aquaculture zones. Our results extend the knowledge of anammox bacteria in marine aquaculture systems and highlight the importance of environmental factors in shaping the community structures of anammox bacteria.