Investigation of the methanotrophic communities of the hot springs of the Uzon caldera,Kamchatka, by molecular ecological techniques

The methane-oxidizing microbial communities inhabiting the bottom sediments of 36 hot springs of the Uzon caldera (Kamchatka, Russia) located in the thermal fields Vostochnoe, Oranzhevoe, and Severnoe, as well as near the lakes Fumarol’noe and Khloridnoe and the Izvilistyi stream, were studied. Methanotrophic bacteria were detected by PCR and FISH in only 8 hot springs. The highest numbers of copies of the pmoA gene (molecular marker of methanotrophy) (2.8 × 10⁷ and 1.1 × 10⁷ copies/mL sediment) were detected in the Kul’turnyi and Kvadrat springs; however, in other springs, the numbers of the pmoA gene copies were significantly lower (5.4 × 10³–2.8 × 10⁶ copies/mL sediment). By using the FISH method, only type I methanotrophs were detected in these springs, with their percentage ranging from 0.3 to 20.5% of the total number of eubacteria. PCR-DGGE analysis of the pmoA gene showed that the diversity of methanotrophs was extremely low (no more that two components). Analysis of the deduced PmoA amino acid sequences demonstrated that methanotrophic bacteria of the genus Methylothermus, closely related to representatives of two valid species, widely occurred in the thermal springs near Lake Fumarol’noe. Other bacteria differing considerably from the detected Methylothermus species were detected as well. In the springs with low pH values (2.6–3.8), methanotrophic Gammaproteobacteria most closely related to the genera Methylomonas and Methylobacter were detected for the first time.