Involved in some intermediate steps for the synthesis of the antibiotic polyketide bacillaene which is involved in secondary metabolism. It catalyzes the transfer of the malonyl-CoA group to the acyl-carrier-protein AcpK (Mal-AcpK) (By similarity). holo-[ACP] + malonyl-CoA = CoA + malonyl-[ACP] Antibiotic biosynthesis; bacillaene biosynthesis. Belongs to the FabD family.