title: Riverbed methanotrophy sustained by high carbon conversion efficiency.
abstract: Our understanding of the role of freshwaters in the global carbon cycle is being revised, but there is still a lack of data, especially for the cycling of methane, in rivers and streams. Unravelling the role of methanotrophy is key to determining the fate of methane in rivers. Here we focus on the carbon conversion efficiency (CCE) of methanotrophy, that is, how much organic carbon is produced per mole of CH4 oxidised, and how this is influenced by variation in methanotroph communities. First, we show that the CCE of riverbed methanotrophs is consistently high (~50%) across a wide range of methane concentrations (~10-7000 nM) and despite a 10-fold span in the rate of methane oxidation. Then, we show that this high conversion efficiency is largely conserved (50%± confidence interval 44-56%) across pronounced variation in the key functional gene (70 operational taxonomic units (OTUs)), particulate methane monooxygenase (pmoA), and marked shifts in the abundance of Type I and Type II methanotrophs in eight replicate chalk streams. These data may suggest a degree of functional redundancy within the variable methanotroph community inhabiting these streams and that some of the variation in pmoA may reflect a suite of enzymes of different methane affinities which enables such a large range of methane concentrations to be oxidised. The latter, coupled to their high CCE, enables the methanotrophs to sustain net production throughout the year, regardless of the marked temporal and spatial changes that occur in methane.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Trimmer
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: Felicity C
authors.initials: FC
authors.lastname: Shelley
authors.affiliation: School of Life Sciences, University of Warwick, Coventry, UK.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Purdy
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: Susanna T
authors.initials: ST
authors.lastname: Maanoja
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: Panagiota-Myrsini
authors.initials: PM
authors.lastname: Chronopoulou
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Grey
authors.forename: Grey
authors.initials: G
authors.lastname: Jonathan
mesh_terms: D001419:Bacteria / Q000302:isolation & purification / Q000378:metabolism; D057965:Carbon Sequestration; D019015:Geologic Sediments / Q000737:chemistry* / Q000382:microbiology; D008697:Methane / Q000378:metabolism*; D042083:Methylocystaceae / Q000235:genetics; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000235:genetics; D010802:Phylogeny; D045483:Rivers / Q000737:chemistry* / Q000382:microbiology
chemical_list: D010105:Oxygenases; C021555:methane monooxygenase; D008697:Methane