Use of stable isotope probing to identify bacterial species involved in CO₂ fixation in the water just below the oxycline of the meromictic Lake Suigetsu, Japan

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In this study, stable isotope probing was used to identify a bacterial community involved with bicarbonate fixation in the water just below the oxycline of the meromictic Lake Suigetsu, Japan. Water samples were incubated with ¹³C-labeled bicarbonate under either light or dark conditions. The identity of active bicarbonate-fixing bacteria was revealed by 16S rRNA gene clone library analysis of ¹³C-labeled DNA fractions. Bacterial clones closely related to the green sulfur bacterial genus Chlorobium were detected under light conditions. Clone sequences phylogenetically affiliated with the genera Arcobacter and Desulfocapsa were also detected under light conditions. In the dark incubation, clones belonging to the class Epsilonproteobacteria were detected. Clone sequences belonging to a clade containing the genus Thiomicrospira were also retrieved from dark incubation samples. These results indicated that phylogenetically diverse bacteria might fix CO₂ in the water below the oxycline of Lake Suigetsu.