The consequences of niche and physiological differentiation of archaeal and bacterial ammonia oxidisers for nitrous oxide emissions

The authors are members of the Nitrous Oxide Research Alliance (NORA), a Marie Skłodowska-Curie ITN and research project under the EU's seventh framework program (FP7). GN is funded by the AXA Research Fund and CGR by a Royal Society University Research Fellowship (UF150571) and a Natural Environment Research Council (NERC) Standard Grant (NE/K016342/1). The authors would like to thank Dr Robin Walker and the SRUC Craibstone Estate (Aberdeen) for access to the agricultural plots, Dr Alex Douglas for statistical advice and Philipp Schleusner for assisting microcosm construction and sampling.Peer reviewedPublisher PD

Crenothrix are major methane consumers in stratified lakes

Methane-oxidizing bacteria represent a major biological sink for methane and are thus Earth's natural protection against this potent greenhouse gas. Here we show that in two stratified freshwater lakes a substantial part of upward-diffusing methane was oxidized by filamentous gamma-proteobacteria related to Crenothrix polyspora. These filamentous bacteria have been known as contaminants of drinking water supplies since 1870, but their role in the environmental methane removal has remained unclear. While oxidizing methane, these organisms were assigned an 'unusual' methane monooxygenase (MMO), which was only distantly related to 'classical' MMO of gamma-proteobacterial methanotrophs. We now correct this assignment and show that Crenothrix encode a typical gammaproteobacterial PmoA. Stable isotope labeling in combination swith single-cell imaging mass spectrometry revealed methane-dependent growth of the lacustrine Crenothrix with oxygen as well as under oxygen-deficient conditions. Crenothrix genomes encoded pathways for the respiration of oxygen as well as for the reduction of nitrate to N2O. The observed abundance and planktonic growth of Crenothrix suggest that these methanotrophs can act as a relevant biological sink for methane in stratified lakes and should be considered in the context of environmental removal of methane

Thermodynamic and hydrochemical controls on CH4 in a coal seam gas and overlying alluvial aquifer: new insights into CH4 origins

Using a comprehensive data set (dissolved CH(4), δ(13)C-CH(4), δ(2)H-CH(4), δ(13)C-DIC, δ(37)Cl, δ(2)H-H(2)O, δ(18)O-H(2)O, Na, K, Ca, Mg, HCO(3), Cl, Br, SO(4), NO(3) and DO), in combination with a novel application of isometric log ratios, this study describes hydrochemical and thermodynamic controls on dissolved CH(4) from a coal seam gas reservoir and an alluvial aquifer in the Condamine catchment, eastern Surat/north-western Clarence-Moreton basins, Australia. δ(13)C-CH(4) data in the gas reservoir (−58‰ to −49‰) and shallow coal measures underlying the alluvium (−80‰ to −65‰) are distinct. CO(2) reduction is the dominant methanogenic pathway in all aquifers, and it is controlled by SO(4) concentrations and competition for reactants such as H(2). At isolated, brackish sites in the shallow coal measures and alluvium, highly depleted δ(2)H-CH(4) (<310‰) indicate acetoclastic methanogenesis where SO(4) concentrations inhibit CO(2) reduction. Evidence of CH(4) migration from the deep gas reservoir (200–500 m) to the shallow coal measures (<200 m) or the alluvium was not observed. The study demonstrates the importance of understanding CH(4) at different depth profiles within and between aquifers. Further research, including culturing studies of microbial consortia, will improve our understanding of the occurrence of CH(4) within and between aquifers in these basins