HEAT-TOLERANT METHANOTROPHIC BACTERIA FROM THE HOT-WATER EFFLUENT OF A NATURAL-GAS FIELD

Methanotrophic bacteria were isolated from a natural environment poten tially favorable to heat-tolerant methanotrophs. An improved colony pl ate assay was developed and used to identify putative methanotrophic c olonies with high confidence. Fourteen new isolates were purified and partially characterized. These new isolates exhibit a DNA sequence hom ology of up to 97% with the conserved regions in the mmoX and mmoC gen es of the soluble methane monooxygenase (MMO)-coding gene duster of Me thylococcus capsulatus Bath. The copper regulation of soluble MMO expr ession in the same isolates, however, differs from that of M. capsulat us Bath, as the new isolates can tolerate up to 0.8 mu M copper withou t loss of MMO activity while a drastic reduction of MMO activity occur s already at 0.1 mu M copper in M. capsulatus Bath. The isolates can b e cultivated and utilized at elevated temperatures, and their copper- and heat-tolerant MMO activity makes these bacteria ideal candidates f or future biotechnological use.