Characteristics of aerobic methane-oxidising bacterial community at the sea-floor surface of the Nankai Trough

Abstract

Methane hydrate is one of the new energy sources, but methane leakage could cause environmental issues such as marine ecosystem changes and global warming. The methane-oxidising bacterial (MOB) community could reflect the methane concentration, thus it may be an indicator of methane leakage. We obtained two sea-floor surface samples from a methane seep area and 12 samples from other general sea-floor areas of the Nankai Trough for the detection and phylogenetic analysis of the particulate methane monooxygenase (pmoA) gene. Using quantitative polymerase chain reaction analysis, the methane seep samples were found to have 106 copies of the pmoA gene per gram of sediment, whereas the general sea-floor area samples of the Nankai Trough contained 103–104 copies of the gene per gram of sediment. Phylogenetic analysis of the pmoA gene sequences showed that the sequences detected in the general and methane seep area samples differed significantly. Specifically, the pmof1–pmor primer pair could detect pmoA genes for the methane seep area, whereas pmoA gene from the general seafloor samples could be detected only using the A189–mb661 primer pair. The results of this study may facilitate the detection of unintended leakage of methane at methane hydrate production sites by monitoring MOB communities using pmoA-targeted phylogenetic analysis and quantification.