Vertical Distribution of Bathyarchaeotal Communities in Mangrove Wetlands Suggests Distinct Niche Preference of Bathyarchaeota Subgroup 6.

Bathyarchaeota is a diverse, abundant, and widespread archaeal phylum that may play an important role in global carbon cycling. The vertical distribution of Bathyarchaeota and environmental impact on bathyarchaeotal community in deep-sea and lake sediments are known; however, little information is available on Bathyarchaeota in eutrophic and brackish environments, such as mangrove wetlands. In the current study, we investigated the bathyarchaeotal community in the mangrove ecosystem of Futian Nature Reserve, Shenzhen. By slicing the profile into 2-cm layers from the surface to bottom, 110 sediment samples were obtained from three mangrove and three mud flat profiles. High-throughput sequencing of archaeal 16S rRNA genes, quantification of bathyarchaeotal 16S rRNA genes with optimized quantitative primers, and the ensuing statistical analyses revealed the vertical distribution of Bathyarchaeota in the mangrove ecosystem, indicating that Bathyarchaeota was the dominant archaeal phylum therein, with Bathyarchaeota subgroups 6, 8, 15, and 17 as the most abundant subgroups. The abundance of Bathyarchaeota was higher in the mangrove than in the mud flat and other oligotrophic or freshwater habitats. Total organic carbon (TOC) and nitric oxide were significantly correlated with the abundance of Bathyarchaeota, and pH was the major factor shaping the community composition. Further, the data suggested that Bathyarchaeota subgroup 6 preferentially dwelled in slightly acidic, high TOC, and subsurface environments, indicating a potentially distinct role in the global geochemical cycle. These findings expand the knowledge of the distribution and niche preference of Bathyarchaeota, emphasizing the need for continuous characterization of bathyarchaeotal subgroups.