Microbial Diversity And Microbe-environment Relationship In Sediments From Qi'ao Island (Pearl River Estuary)

Sediments samples from Qi'ao Island(Pearl River Estuary), southern China, were analyzed to gain insight into the microbes present, especially which involved in methane metabolism by molecular phylogenetic methods and geochemical data analyses.Profiles of CH4 and SO₄^2- in pore-water with the increasing depth for the sedimentary cores were detected. The results showed that methane concentration changes dramatically at the base of the sulfate-reducing zone and sulfate concentration gradients are linear. The geochemical profiles of pore-water render indirect evidence for sulfate-reducing process and methane metabolism, especially anaerobic oxidation of methane(AOM).The analysis of PLFA shows that microbial diversity was decreased as the depth increased in the sediments and there are great differences in community constructure in top, middle and bottom sediments. Sulfate-reducing bacteria dominated in the sediment core and sulfur-oxidizing bacteria were dominated in surface sediment(0-12cm). None of lipid biomarkers associated with methanotrophs were detected in sediments, suggesting an extremely low abundance of methanotrophs. These results are supported by the molecular phylogenetic methods 16S rRNA gene analysis revealed that most bacteria along the sediment core belonged toδ-proteobacteria.γ-,β-,α-,ε-proteobacteria and aerobic methane oxidization were also detected in the study. Archaeal sequence analysis showed that the archaeal diversity was high in estuarine sediments. The Crenarchaota was predominated along the sediment core. The community structure and diversity of archaea shifted greatly within vertical distance. Most of archaeal sequences from the surface layer fell into marine nitrification Creanarchaeon; most of archaeal sequences from the middle and bottom layers were closely related to environmental clones from rich-methane environments and 15% archaeal sequences in the middle layer clustered with Methanosarcinales and Methanomicrobiales. The number of bacteria(5.2-14.6×10⁸ 16S rDNA copies/g sediment) is 1-2 orders of magnitude higher than that of Archaea(0.19-6.5×10⁷ 16S rDNA copies/g sediment) alonge the sediments core.The specific primers for the microbes involving in the metabolism of CH₄ were used to evaluate the roles of microbes in methane cycle in estuarine sediment. Functional gene analysis of the pmoA revealed that type I methanotrophs and typeâ…¡methanotrophs were both detected in this sediment core and typeâ… methanotrophs were the dominant aerobic methanotrophs. Quantitative-PCR suggested that the number of methanotrophs was low and below the detection limit of 2.8×10⁴ pmoA copies/g sediment. The investigation based on the mcrA gene indicated there were present methane production and anaerobic methane oxidization along the sediment core. Methanomicrobiales was predominated along the sediment core. Howere, Rice clusterI was dominated in the sulfate-methane transition zone, suggesting that the group could play an important role in anaerobic methane-oxidization. The biomass of methanogens were 0.99±0.74-5.90±0.22×10⁵ mcrA copies/g sediment.Our data suggest that the community structure and diversity of microorganisms can shift greatly within small vertical distance, possibly in response to changes in the physical and chemical conditions and AOM can dominate in methane oxidation in Pearl River Estuary system. This study provides for the first time an insight into the diversity of microbes in the Pearl River Estuary sediments, especially which participated in methan metabolism.