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

Methanotrophic bacteria were isolated from a natural environment potentially favorable to heat-tolerant methanotrophs. An improved colony plate assay was developed and used to identify putative methanotrophic colonies with high confidence. Fourteen new isolates were purified and partially characterized. These new isolates exhibit a DNA sequence homology of up to 97% with the conserved regions in the mmoX and mmoC genes of the soluble methane monooxygenase (MMO)-coding gene duster of Methylococcus capsulatus Bath. The copper regulation of soluble MMO expression in the same isolates, however, differs from that of M. capsulatus Bath, as the new isolates can tolerate up to 0.8 mu M copper without loss of MMO activity while a drastic reduction of MMO activity occurs already at 0.1 mu M copper in M. capsulatus Bath. The isolates can be cultivated and utilized at elevated temperatures, and their copper- and heat-tolerant MMO activity makes these bacteria ideal candidates for future biotechnological use.