Mechanism of oxidation of carbon monoxide by bacteria

Double label experiments were performed employing ¹³CO and either H₂¹⁸O or ¹⁸O₂ in the presence of a CO utilizing bacterium. CO₂ generated was trapped and $\text{m}\text{e}$ ratios $\text{47}\text{45}$ showed that the second oxygen atom in the oxidation of CO to CO₂ by this bacterium comes neither from O₂ nor H₂O.