Advances in thermoacidophilic methanotrophs from extreme environments

Methane-oxidizing bacteria(methanotrophs) play an important role in the biogeochemical carbon cycle and in controlling global climate change,by converting methane to carbon dioxide or biomass.Although these bacteria have been isolated from a variety of environments,most of which grow best at neutral pH(5-8) and moderate temperature ranges(20-35℃).Based on the phylogenetic analysis,methanotrophs are classified into type I and type II,which belong to the gamma-and alpha-Proteobacteria,respectively.Very recently,three independent studies have isolated methane-oxidizing microorganisms from extreme thermoacidophilic environments with pH values of approximately 1 and temperatures higher than 50℃,these nonproteobacterial strains were all identified as members of the phylum Verrucomicrobia.These new and unusual studies will undoubtedly expand the known phylogenetic and functional diversity of methanotrophs,also indicate that novel methane oxidizing pathways and mechanisms could exist in the methanotrophs.This review illustrates the latest advances in thermoacidophilic methanotrophs,based on the recent three reports on methane oxidation in the extreme environments.