Do methanotrophic and thermoacidophilic Verrucomicrobia possess a biogeographic structure?

Aerobic methane-oxidizing bacteria (MOB) are a ubiquitous group of microorganisms with the capability to use methane as a sole energy and carbon source. Until 2007-2008 when three strains of thermoacidophilic Verrucomicrobial methanotrophs, tentatively named ‘Methylacidiphilum’ spp., were isolated, all MOB belonged to the alpha and gamma subclasses of Proteobacteria. ´Methylacidiphilum´ spp. isolated from distant terrestrial geothermal areas (Kamchatka, Italy and New Zealand) possess three complete but phylogenetically distinct pmoCAB operons, which encode the three subunits of the particulate methane monooxygenase (pMMO) key metabolic enzyme. The low non-synonymous versus synonymous base substitution rates indicate that each pmo orthologue plays an important functional role. The Verrucomicrobial pmo genes display a distant relationship to the Proteobacterial homologues and their distinct phylogenetic clustering indicates an ancient divergence of methanotrophic metabolism. Additional thermoacidophilic and methanotrophic Verrucomicrobia strains were recently isolated from a variety of geothermal locations world-wide; Yellowstone National Park, Iceland, The Azores and The Philippines. Sequence analysis of their rRNA and pmoA genes indicates a close phylogenetic relationship among the isolates and with the previously characterised ´Methylacidiphilum´ isolates. However, serological analyses using rabbit antiserum raised against whole cells of Kam1 revealed significant differences in serological properties among the strains as determined by ELISA and Western blot profiling. Serology in combination with gene sequence analysis might be a powerful tool to determine a possible biogeographic structure among this novel group of methanotrophs. These analyses can possibly give more information about their evolution and adaptation to their narrow and geographically restricted environmental niches.