Investigation of the methanogen-related archaeal population structure in shallow sediments of the Pearl River Estuary, Southern China.

Few studies have specifically dealt so far with methanogen-related archaea in estuarine sediments. In this study, methanogen-related archaeal populations were investigated by 16S rRNA gene clone library, T-RFLP analysis, and methanogen enrichment in Pearl River estuarine sediments. The majority of obtained sequences in clone libraries and T-RF peaks from T-RFLP analysis were assigned mainly to Methanosaeta, Methanomicrobiales, and Methanosarcinales/ANME. The fragments of Methanosarcinales/ANME were most dominant group (mean 47%) and composed largely of ANME-2a which are characterized as anaerobic methane oxidizing archaea in broad environments. Furthermore Methanosaeta and Methanomicrobiales accounted for 23 and 29% of fragments, respectively, for all depths. Therefore, the presence of Methanomicrobiales and Methanosaeta in Pearl River estuarine sediments was indicative of both acetoclastic and hydrogenotrophic methanogenesis. In addition, the enrichments of methanogens also suggested the presence of acetoclastic and hydrogenotrophic methanogens in Pearl River estuarine sediments. This study is a significant step toward understanding methane cycling association of representative archaea in estuarine environments.