Nigericin (Nig)

Nigericin is an antibiotic derived from Streptomyces hygroscopicus. Nigericin was among the first polyether ionophores to be discovered, but its biosynthesis remains obscure. The biosynthetic gene cluster for nigericin has been serendipitously cloned from Streptomyces sp. DSM4137, and deletion of this gene cluster abolished the production of both nigericin and the closely related metabolite abierixin. Detailed comparison of the nigericin biosynthetic genes with their counterparts in the biosynthetic clusters for other polyketides has prompted a significant revision of the proposed common pathway for polyether biosynthesis. In nigericin, nanchangmycin, and monensin, an unusual ketosynthase-like protein, KSX, transfers the initially formed linear polyketide chain to a discrete acyl carrier protein, ACPX, for oxidative cyclization.