Seasonal variations of n-damo bacterial community in the subtropical Mai Po mangrove wetland of Hong Kong

Mangrove wetland is one of the most important ecosystems along the coast and often suffers from global climate change as well as the anthropogenic activities. Nitrite-dependent anaerobic methane oxidization (n-damo) bacteria play an important role in linking the microbial geochemical cycles of carbon and nitrogen in the wetlands, but the pattern of their diversity and abundance to a changing mangrove wetland is poorly understood. In the present work, we investigated the seasonal variations of n-damo bacteria in vegetated and non-vegetated sediments of a subtropical mangrove wetland by amplifying 16 S rDNA and pmoA gene sequences. Results indicated that n-damo bacterial communities in the surface sediments maintained freshwater lineage characteristics as the majority after the long rainy season, while the abundance of marine lineages dominated in all the subsurface sediments. Shannon-Wiener and Chao1 indices based on 16 S rDNA gene sequences decreased largely in reed sediments by the end of rainy season, but increased in both surface and subsurface sediments of mangrove and mudflat zones, especially in the non-vegetated surface sediments. The majority of n-damo bacterial pmoA gene sequences shifted from Cluster SCS-2 to Cluster SCS-1 by the end of the dry season. Results suggested that Clusters SCS-1 and SCS-3 would be more likely detected in relatively pristine marine sediments, while Cluster SCS-2 tended to be abundant in coastal habitats with a strong terrestrial/anthropogenic influence. Vegetation had either direct or indirect influence on the decrease of alpha diversity of n-damo pmoA gene when the abundance showed an increase by the end of the wet season. The abundances of n-damo bacteria increased by two orders of magnitude to 5.1–9.4 × 10⁷ copies/g dry sediment after the rainy season. Results suggested that NH₄⁺ and NH₄⁺/NO₂⁻ were significant factors governing the diversity of n-damo community in mangrove wetland sediments. The findings of this present work provided an in-depth understanding on the variations of n-damo bacterial community to seasonal changes in the subtropical mangrove wetland.