Methane release from sediment seeps to the atmosphere is counteracted by highly active Methylococcaceae in the water column of deep oligotrophic Lake Constance.
Methane emissions from freshwater environments contribute substantially to global warming but are under strong control of aerobic methane-oxidizing bacteria. Recently discovered methane seeps (pockmarks) in freshwater lake sediments have the potential to bypass this control by their strong outgassing activity. Whether this is counteracted by pelagic methanotrophs is not well understood yet. We used a (3)H-CH4-radiotracer technique and pmoA-based molecular approaches to assess the activity, abundance and community structure of pelagic methanotrophs above active pockmarks in deep oligotrophic Lake Constance. Above profundal pockmarks, methane oxidation rates (up to 458 nmol CH4 l(-1) d(-1)) exceeded those of the surrounding water column by two orders of magnitude and coincided with maximum methanotroph abundances of 0.6% of the microbial community. Phylogenetic analysis indicated a dominance of members of the Methylococcaceae in the water column of both, pockmark and reference sites, with most of the retrieved sequences being associated with a water-column specific clade. Communities at pockmark and reference locations also differed in parts, which was likely caused by entrainment of sediment-hosted methanotrophs at pockmark sites. Our results show that the release of seep-derived methane to the atmosphere is counteracted by a distinct methanotrophic community with a pronounced activity throughout bottom waters.
Department of Biology, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany.
Maren
M
Bornemann
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Meeresstation Helgoland, Kurpromenade 201, D-27498 Helgoland, Germany.
Ingeborg
I
Bussmann
Department of Biology, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany.
Lucas
L
Tichy
Department of Biology, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany Department of Civil and Environmental Engineering, Stanford University, 318 Campus Drive, Stanford, CA 94305, USA.
Jörg
J
Deutzmann
Department of Biology, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany.
Bernhard
B
Schink
Department of Biology, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany Michael.Pester@uni-konstanz.de.
Michael
M
Pester
D001272:Atmosphere / Q000032:analysis; D019015:Geologic Sediments / Q000382:microbiology*; D005858:Germany; D060106:Lakes / Q000382:microbiology*; D008697:Methane / Q000378:metabolism*; D008772:Methylococcaceae / Q000145:classification* / Q000302:isolation & purification / Q000378:metabolism*; D064307:Microbiota / Q000502:physiology*; D010084:Oxidation-Reduction; D010802:Phylogeny; D014867:Water; D014871:Water Microbiology
D014867:Water; D008697:Methane
Lake Constance; aerobic methanotrophic bacteria; methane oxidation activity; methane seep; pockmark; water column