Part of the energy-coupling factor (ECF) transporter complex CbiMNOQ involved in cobalt import. The complex confers cobalt uptake upon expression in E.coli; can also transport nickel with a very low affinity. Cofactor biosynthesis; adenosylcobalamin biosynthesis. Forms an energy-coupling factor (ECF) transporter complex composed of an ATP-binding protein (A component, CbiO), a transmembrane protein (T component, CbiQ) and 2 possible substrate-capture proteins (S components, CbiM and CbiN) of unknown stoichimetry. Expression of just CbiMN in E.coli confers some cobalt uptake. Belongs to the CbiM family.