Methanotrophy below pH 1 by a new Verrucomicrobia species

Passing the acid test Bacteria that consume the greenhouse gas methane are potentially important players in the atmospheric budget, with the potential to sop up methane from the Earth's crust that would otherwise contribute to the atmospheric budget. Two new methane-utilizing bacteria have been isolated independently and both break new ground: unlike previous methanotrophic isolates, which are proteobacteria, they belong to the widely distributed Verrucomicrobia phylum. And both isolates display optimum growth and methane oxidation in remarkably acidic conditions, at pHs as low as 0.8 to 2.5. Acidimethylosilex fumarolicum SolV was isolated from a fuming vent on the Solfatara volcano near Naples, Italy, and Methylokorus infernorum from hot soil in the Hell's Gate (Tikitere) geothermal area of New Zealand. The isolation of the acidophilic bacterium Acidimethylosilex fumarolicum SolV from a fumarole is described. Unlike all previous methanotrophic isolates, which belong to the Alpha- or Gammaproteobacteria, it belongs to the widely distributed Verrumicrobia. Mud volcanoes, mudpots and fumaroles are remarkable geological features characterized by the emission of gas, water and/or semi-liquid mud matrices 1 with significant methane fluxes to the atmosphere (10 -1 to 10 3 t y -1 ) 2 , 3 , 4 . Environmental conditions in these areas vary from ambient temperature and neutral pH to high temperatures and low pH. Although there are strong indications for biological methane consumption in mud volcanoes 4 , 5 , no methanotrophic bacteria are known that would thrive in the hostile conditions of fumaroles (temperatures up to 70 °C and pH down to 1.8) 2 . The first step in aerobic methane oxidation is performed by a soluble or membrane-bound methane mono-oxygenase. Here we report that pmoA (encoding the β-subunit of membrane-bound methane mono-oxygenase) clone libraries, made by using DNA extracted from the Solfatara volcano mudpot and surrounding bare soil near the fumaroles, showed clusters of novel and distant pmoA genes. After methanotrophic enrichment at 50 °C and pH 2.0 the most distant cluster, sharing less than 50% identity with any other described pmoA gene, was represented in the culture. Finally we isolated an acidiphilic methanotrophic bacterium Acidimethylosilex fumarolicum SolV belonging to the Planctomycetes/Verrucomicrobia/Chlamydiae superphylum 6 , ‘outside’ the subphyla of the Alpha- and Gammaproteobacteria containing the established methanotrophs. This