CO-oxidizing Microorganisms

Abstract

CO is metabolized by a wide variety of microorganisms. A sharp division exists between aerobic and anaerobic species, as they contain fundamentally different enzyme systems for CO biotransformation. Aerobic CO-oxidizing bacteria may be divided in two groups: metabolic, in which CO oxidation provides energy for growth, and co-metabolic, in which CO is used as pseudo-substrate for the enzyme system, but does not provide a nutritional value (Colby et al. Trends Biotechnol 3:12–17, 1985). The latter is observed during aerobic CO oxidation by methane-oxidizing bacteria employing the methane monooxygenase complex, which is rather unspecific with respect to its substrate (Higgins et al. Nature 286:561–564, 1980; Daniels et al. J Bacteriol 132:118–126, 1977). Aerobic metabolic CO-oxidizing bacteria or aerobic carboxydotrophs use CO as a source of energy, which is oxidized with O₂ as terminal electron acceptor. These bacteria contain a specific CO-tolerant cytochrome b1 oxidase and O₂-insensitive Mo–Fe-flavin carbon monoxide dehydrogenase. The diversity and ecology of bacteria that grow aerobically with CO has been intensively studied and reviewed (Zavarzin and Nozhevnikova Microb Ecol 3:305–326, 1977; Meyer et al. FEMS Microbiol Rev 87:253–260, 1990; Conrad Microbiol Rev 60:609–640, 1996; King and Webber Nat Rev Microbiol 5:107–118, 2007). Aerobic carboxydotrophs include CO-utilizing microorganisms that belong to α-proteobacteria, Firmicutes, and Actinobacteria (Table 3.1).