title: Acid-Tolerant Moderately Thermophilic Methanotrophs of the Class Gammaproteobacteria Isolated From Tropical Topsoil with Methane Seeps.
abstract: Terrestrial tropical methane seep habitats are important ecosystems in the methane cycle. Methane oxidizing bacteria play a key role in these ecosystems as they reduce methane emissions to the atmosphere. Here, we describe the isolation and initial characterization of two novel moderately thermophilic and acid-tolerant obligate methanotrophs, assigned BFH1 and BFH2 recovered from a tropical methane seep topsoil habitat. The new isolates were strictly aerobic, non-motile, coccus-shaped and utilized methane and methanol as sole carbon and energy source. Isolates grew at pH range 4.2-7.5 (optimal 5.5-6.0) and at a temperature range of 30-60°C (optimal 51-55°C). 16S rRNA gene phylogeny placed them in a well-separated branch forming a cluster together with the genus Methylocaldum as the closest relatives (93.1-94.1% sequence similarity). The genes pmoA, mxaF, and cbbL were detected, but mmoX was absent. Strains BFH1 and BFH2 are, to our knowledge, the first isolated acid-tolerant moderately thermophilic methane oxidizers of the class Gammaproteobacteria. Each strain probably denotes a novel species and they most likely represent a novel genus within the family Methylococcaceae of type I methanotrophs. Furthermore, the isolates increase our knowledge of acid-tolerant aerobic methanotrophs and signify a previously unrecognized biological methane sink in tropical ecosystems.
authors.affiliation: Department of Biology, University of Bergen Bergen, Norway.
authors.forename: Tajul
authors.initials: T
authors.lastname: Islam
authors.affiliation: Department of Biology, University of Bergen Bergen, Norway.
authors.forename: Vigdis
authors.initials: V
authors.lastname: Torsvik
authors.affiliation: Department of Biology, University of BergenBergen, Norway; Uni Environment, Uni ResearchBergen, Norway.
authors.forename: Øivind
authors.initials: Ø
authors.lastname: Larsen
authors.affiliation: Oceans and Atmosphere, CSIRO, Hobart TAS, Australia.
authors.forename: Levente
authors.initials: L
authors.lastname: Bodrossy
authors.affiliation: Department of Biology, University of Bergen Bergen, Norway.
authors.forename: Lise
authors.initials: L
authors.lastname: Øvreås
authors.affiliation: Department of Biology, University of BergenBergen, Norway; Centre for Geobiology, University of BergenBergen, Norway.
authors.forename: Nils-Kåre
authors.initials: NK
authors.lastname: Birkeland
keywords: Gammaproteobacteria; acid-tolerant; methanotroph; moderately thermophilic; pMMO; terrestrial