CO utilization by a CO2-requiring extremely oligotrophic bacterium, Rhodococcus erythropolis N9T-4 was found when CO2 was removed from the culture environment before cultivation, suggesting that this bacterium can convert CO into CO2. However, the gene encoding putative CO dehydrogenase large subunit in N9T-4 was not induced by CO. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.