Downloaded from www.microbiologyresearch.org by IP: 54.167.185.24 On: Fri, 28 Oct 2016 13:32:00 International Journal of Systematic and Evolutionary Microbiology (2000), 50, 955–969 Printed in Great Britain Methylocella palustris gen. nov., sp. nov., a new methane-oxidizing acidophilic bacterium from peat bogs, representing a novel subtype of serine-pathway methanotrophs Svetlana N. Dedysh, 1,5 Werner Liesack, 2 Valentina N. Khmelenina, 3 Natalia E. Suzina, 3 Yuri A. Trotsenko, 3 Jeremy D. Semrau, 4 Amy M. Bares, 4 Nicolai S. Panikov 1 and James M. Tiedje 5 Author for correspondence : Svetlana N. Dedysh. Tel : 7 95 135 0591. Fax: 7 95 135 6530. e-mail : dedyshinmi.host.ru 1 Institute of Microbiology, Russian Academy of Sciences, Moscow 117811, Russia 2 Max-Planck-Institut fu  r Terrestrische Mikrobiologie, D-35043 Marburg, Germany 3 Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow region 142292, Russia 4 Department of Civil and Environmental Engineering, The University of Michigan, Ann Arbor, MI 48109-2125, USA 5 Center for Microbial Ecology, Michigan State University, East Lansing, MI 48824-1325, USA A new genus, Methylocella, and a new species, Methylocella palustris, are proposed for three strains of methane-oxidizing bacteria isolated from acidic Sphagnum peat bogs. These bacteria are aerobic, Gram-negative, colourless, non-motile, straight and curved rods that utilize the serine pathway for carbon assimilation, multiply by normal cell division and contain intracellular poly-β- hydroxybutyrate granules (one at each pole). These strains use methane and methanol as sole sources of carbon and energy and are moderately acidophilic organisms with growth between pH 45 and pH 70, the optimum being at pH 50–55. The temperature range for growth is 10–28 SC with the optimum at 15–20 SC. The intracytoplasmic membrane system is different from those of type I and II methanotrophs. Cells contain an extensive periplasmic space and a vesicular membrane system connected to the cytoplasmic membrane. The strains grew only on media with a low salt content (02–05gl N1 ). All three strains were found to possess soluble methane monooxygenase and are able to fix atmospheric nitrogen via an oxygen-sensitive nitrogenase. No products were observed in a PCR with particulate methane monooxygenase-targeted primers ; hybridization with a pmoA probe was also negative. The major phospholipid fatty acids are 18 : 1 acids. The GMC content of the DNA is 612 mol %. The three strains share identical 16S rRNA gene sequences and represent a novel lineage of methane-oxidizing bacteria within the α-subclass of the class Proteobacteria and are only moderately related to type II methanotrophs of the Methylocystis–Methylosinus group. The three strains are most closely related to the acidophilic heterotrophic bacterium Beijerinckia indica subsp. indica (965 % 16S rDNA sequence similarity). Collectively, these strains comprise a new species and genus Methylocella palustris gen. nov., sp. nov.; strain K T ( ATCC 700799 T ) is the type strain. Keywords : Methylocella palustris gen. nov., sp. nov., acidophilic methane-oxidizing bacteria, serine-pathway methanotrophs INTRODUCTION Methane-oxidizing bacteria (MOB) are a ubiquitous group of micro-organisms possessing the unique ability to utilize methane as the sole source of carbon ................................................................................................................................................. Abbreviations : FAME, fatty acid methyl ester ; ICM, intracytoplasmic membrane ; MOB, methane-oxidizing bacteria ; pMMO, particulate meth- ane monooxygenase ; sMMO, soluble methane monooxygenase. The EMBL/GenBank/DDBJ accession number for the 16S rRNA gene of Methylocella palustris strain K T is Y17144. and energy. The current classification separates all the known methanotrophs into three groups (types I, II and X) by multiple criteria, including cell morphology, the arrangement of intracytoplasmic membranes, the pathway for formaldehyde assimilation, the DNA GC content and the major phospholipid fatty acids. Both 5S rRNA and 16S rRNA sequence analyses indicated that all known MOB form phylogenetically coherent clusters within the α- and γ-subclasses of the Proteobacteria (Hanson & Hanson, 1996). Although MOB have been isolated from diverse 01279  2000 IUMS 955