A novel thermophilic methane-oxidising gamma-Proteobacterium

A novel thermophilic methane-oxidising bacterium was isolated from undergro und hot springs in Hungary. Strain HB grew on methane at up to 72 degrees C , the highest recorded growth temperature for a methanotroph. 16S rDNA phyl ogenetic analysis showed that strain HB was the first known representative of a novel, deep-branching group of the gamma-Proteobacteria quite distinct from extant methanotrophs. The nucleotide sequence of pmoA, encoding parti culate methane monooxygenase, was determined for this novel thermophile. Se quence comparison showed that the methane monooxygenase of this strain was most closely related to that of Methylocaldum and Methylococcus species. Pa rticulate methane monooxygenase gene fragments having a high degree of iden tity to that of pmoA from strain HB were amplified by PCR from DNA isolated from thermophilic methane-oxidising enrichments inoculated with hot spring samples (55-70 degrees C) from Japan, suggesting that this novel genus, fo r which we informally suggest the name 'Methylothermus', is widespread in t hermophilic environments. (C) 1999 Federation of European Microbiological S ocieties. Published by Elsevier Science B.V. All rights reserved.