11:15 AM - 11:30 AM
[MIS21-03] Aerobic and anaerobic methanotrophs and their activity in methane-seep sediments of the northeastern Japan Sea offshore Sakata assessed by 13C-labelling experiments
Keywords:Aerobic/anaerobic oxidation of methane, Archaea, Bacteria, 13C-labelling, Lipid biomarker
Microbial oxidation of methane plays a major role in regulating the release of subsurface methane into the ocean and atmosphere. Up to 80% of methane migrating to the seafloor is consumed by aerobic and/or anaerobic methane-oxidizing microorganisms (Reeburgh, 2007; Boetius and Wenzhöfer, 2013). Identifying microbes involved in methane oxidation and assessing their activity in sediments can provide insights into subsurface microbial diversity and methane dynamics of gas hydrate systems. However, activity of both aerobic and anaerobic methanotrophs in marine sediments has been poorly investigated. Although lipid biomarkers are utilized as strong tools to examine the community structure and distribution of microbes in sediments, they have not been clearly linked to their source organisms, especially aerobic methanotrophs (e.g., Rush et al., 2016).
By combining genetic analysis, lipid biomarker analysis, and incubation experiments with 13C-labelled methane, this study investigated aerobic/anaerobic methanotrophs and their activity in methane-seep sediments of the northeastern Japan Sea offshore Sakata. Push core samples were taken from sediments with microbial-mats like surface and used for the analyses. The sediments from 0–10 cm below seafloor (bsf) were aerobically and anaerobically incubated with CH4 (20% 13C) for more than 100 days at 4°C, both showing 13C uptake into dissolved inorganic carbon due to oxidation of 13C-methane. The detection of both aerobic and anaerobic methanotroph activity in the same sediments is distinct from the predominance of either aerobic or anaerobic methanotrophs in mud volcano sediments (Niemann et al., 2006), and has important implications for the methane flux at the study site. Anaerobic oxidation of 13C-methane was also observed at a much lower rate for deeper sediments (10–14 cmbsf). High-throughput sequencing of archaeal and bacterial 16S rRNA genes showed that anaerobic methane-oxidizing archaeal group ANME-1 was highly abundant in the sediments. The relative abundance of the ANME-1 archaea increased from less than 5% at the surface to more than 50% of the whole microbial communities at 10–14 cmbsf. Lipid biomarkers specific for archaea including ANME groups, archaeol and hydroxyarchaeol, were detected in trace amounts in the surface sediments above 4 cmbsf. From the same sediments, bacteriohopanepolyols, which are characteristic biomarkers for aerobic methanotrophs and other bacteria, were detected as degradation products released by periodic acid treatment of another aliquot of the total lipid extracts. Ongoing analyses of archaeal and bacterial lipids in the deeper sediments and 13C uptake into the lipids will specify which lipids were produced by the source methanotrophs deduced from the gene sequences. The results for the 13C-labelling approach could improve the use of lipid biomarkers in studying the composition, distribution, and activity of methanotrophic communities in methane-rich sediments and sedimentary rocks.
This study was conducted as a part of the methane hydrate research project funded by the Ministry of Economy, Trade and Industry (METI), Japan.
By combining genetic analysis, lipid biomarker analysis, and incubation experiments with 13C-labelled methane, this study investigated aerobic/anaerobic methanotrophs and their activity in methane-seep sediments of the northeastern Japan Sea offshore Sakata. Push core samples were taken from sediments with microbial-mats like surface and used for the analyses. The sediments from 0–10 cm below seafloor (bsf) were aerobically and anaerobically incubated with CH4 (20% 13C) for more than 100 days at 4°C, both showing 13C uptake into dissolved inorganic carbon due to oxidation of 13C-methane. The detection of both aerobic and anaerobic methanotroph activity in the same sediments is distinct from the predominance of either aerobic or anaerobic methanotrophs in mud volcano sediments (Niemann et al., 2006), and has important implications for the methane flux at the study site. Anaerobic oxidation of 13C-methane was also observed at a much lower rate for deeper sediments (10–14 cmbsf). High-throughput sequencing of archaeal and bacterial 16S rRNA genes showed that anaerobic methane-oxidizing archaeal group ANME-1 was highly abundant in the sediments. The relative abundance of the ANME-1 archaea increased from less than 5% at the surface to more than 50% of the whole microbial communities at 10–14 cmbsf. Lipid biomarkers specific for archaea including ANME groups, archaeol and hydroxyarchaeol, were detected in trace amounts in the surface sediments above 4 cmbsf. From the same sediments, bacteriohopanepolyols, which are characteristic biomarkers for aerobic methanotrophs and other bacteria, were detected as degradation products released by periodic acid treatment of another aliquot of the total lipid extracts. Ongoing analyses of archaeal and bacterial lipids in the deeper sediments and 13C uptake into the lipids will specify which lipids were produced by the source methanotrophs deduced from the gene sequences. The results for the 13C-labelling approach could improve the use of lipid biomarkers in studying the composition, distribution, and activity of methanotrophic communities in methane-rich sediments and sedimentary rocks.
This study was conducted as a part of the methane hydrate research project funded by the Ministry of Economy, Trade and Industry (METI), Japan.