Isolation and characterization of CO2-fixing hydrogen-oxidizing marine bacteria

A CO2-fixing bacterium, strain YN-1, that can fix CO2 under chemoautotrophic conditions but not photoautotrophic conditions was isolated from seawater. Identification of the isolate was carried out using biochemical tests and 16S rDNA sequence analysis, and its characteristics were investigated. From the results of partial 16S rDNA sequence analysis, strain YN-1 showed low identity with previously reported hydrogen-oxidizing bacteria, Hydrogenovibrio marinus MH-110 and Hydrogenophilus thermoluteolus. This result indicates that strain YN-1 may be a new hydrogen-oxidizing marine bacterium. Strain YN-1 showed considerable CO2 fixation ability during continuous cultivation even at high CO2 concentration. Strain YN-1 used H2 and CO2 as energy and carbon sources, respectively. Growth characteristics were examined in batch and continuous cultivation with a view to improving the CO2 fixation rate. The results showed that CO2 fixation occurred in the absence of a light source and that the strain exhibited good growth at high CO2 concentration (40%). On the other hand, the dry cell weight was 13.4 g/l following continuous cultivation for 76 h in 10% CO2 (0.1 l/min), and at that time the amount of fixed CO2 was 18.08 g CO2/l. This indicates that strain YN-1 can efficiently fix CO2 even at high CO2 concentrations, which would allow its application to the removal of industrially discharged CO2.