Involved in the maturation of [NiFe] hydrogenases. Involved in the biosynthesis of the Fe(CN)(2)CO cofactor (PubMed:16412426). HybG delivers iron-bound CO(2) to HypD where reduction to CO probably occurs (PubMed:23851071). In complex with HypD, accepts the cyanide ligand generated by HypF and HypE, and also coordinates the carbon monoxide ligand (By similarity). Involved in the maturation of the hydrogenase 2. Also participates in the maturation of hydrogenase 1 (PubMed:11292801). Protein modification; [NiFe] hydrogenase maturation. Forms a complex with HypD and HypE (PubMed:16412426). Interacts with the precursor form of HybC (pre-HybC), the large subunit of hydrogenase 2, and with HyaB, the large subunit of hydrogenase 1 (PubMed:11292801, PubMed:16412426). Deletion of the gene abolishes the generation of active hydrogenase 2, but only reduces hydrogenase 1 activity. It does not affect the maturation of hydrogenase 3. Deletion of both hybG and hypC completely abolishes hydrogenase activity. Belongs to the HupF/HypC family.