Methane release from sediment seeps to the atmosphere is counteracted by highly active Methylococcaceae in the water column of deep oligotrophic Lake Constance

Abstract

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.

Microbial megacities fueled by methane oxidation in a mineral spring cave

“…As shown above, this had the highest methane oxidation rates and methanotroph/methylotroph abundance. The CH 4 consumption rates of up to 25 μmol g biofilm FW −1 day −1 were >4 orders of magnitude higher than rates recently reported for the water column above methane seeps in Lake Constance ( Bornemann et al , 2016 ) and in a similar high range as reported for other methane-venting geothermal sites ( Gagliano et al , 2016 ; Lennon et al , 2017 ). Upscaling this for biofilm mass estimates in the cave, a potential methane turnover of ~1.6 mol day −1 (~35.8 l CH 4 day −1 ) can be extrapolated for the submersed biofilms alone.…”

Ubiquity and quantitative significance of bacterioplankton lineages inhabiting the oxygenated hypolimnion of deep freshwater lakes

“…Recent studies have suggested that dissolved organic matter in the oxygenated hypolimnion is enriched by the slowly consumed semilabile fraction ( Maki et al , 2010 ) and can be transformed into a more recalcitrant form by microbes ( Thottathil et al , 2013 ; Hayakawa et al , 2016 ), as shown by the microbial carbon pump theory proposed for the ocean ( Ogawa et al , 2001 ; Yamashita and Tanoue, 2008 ; Jiao and Zheng, 2011 ; Hansell, 2013 ). Other studies have demonstrated that nitrification ( Small et al , 2013 ), dark carbon fixation ( Callieri et al , 2014 ) and methane oxidation ( Murase and Sugimoto, 2005 ; Bornemann et al , 2016 ) are also present in the oxygenated hypolimnion. The bacterioplankton inhabiting this realm are responsible for these important biogeochemical processes; thus, their ecophysiological characteristics should be studied.…”

Low Abundance of Methanotrophs in Sediments of Shallow Boreal Coastal Zones With High Water Methane Concentrations

“…In addition to Proteobacteria, the phylum Verrucomicrobia has been found to contain thermophilic aerobic methanotrophs (belonging to the family Methylacidiphilaceae) (Erikstad and Birkeland, 2015). The importance of methanotrophs to limit CH 4 emission has previously been shown, e.g., Bornemann et al (2016) used pMMO primers (subunit A, pmoA) and clone-libraries to identify methanotrophs (taxonomic order Methylococcales) in the pelagic area of Lake Constance, and found that these bacteria contributed substantially to CH 4 removal in the bottom water directly above the sediment surface. Bacterial members belonging to the order Methylococcales are ubiquitous (Smith et al, 2018), and metagenome plus metatranscriptome analysis have shown that they dominate aerobic CH 4 oxidation in wetland soil (Smith et al, 2018), and are important in removing CH 4 escaping from benthic CH 4 seeps (Taubert et al, 2019).…”