(a) The FK506 producer S. sp. KCTC 11604BP synthesizes allylmalonyl-CoA, which derives from a multi-step pathway involving the ketosynthase TcsB, the cognate acyltransferase and acyl-carrier protein TcsA, the crotonyl-CoA carboxylase TcsC, and the dehydrogenase TcsD. (b) The enzymatic machineries for FK506 (a) and isobutyrylmalonyl-CoA (c) biosynthesis were combined from two different streptomycetes to generate the hybrid pathway of 36-methyl-FK506 in Streptomyces sp. KCTC 11604BP ΔtcsB. (c) The ansalactam producer S. sp. CNH189 assembles isobutyrylmalony-CoA using the FabH-like β-ketoacyl-ACP-synthase AnlF, the dehydrogenase AnlG, and the crotonyl-CoA carboxylase AnlE.