Highly reducing polyketide synthase; part of the gene cluster that mediates the biosynthesis of viriditoxin, one of the 'classical' secondary metabolites produced by fungi and that has antibacterial activity (PubMed:31304040). The first step is performed by the polyketide synthase VdtA which condenses one acetyl-CoA and 6 malonyl-CoA units to form the heptaketide monomer backbone of viriditoxin (PubMed:31304040). The product of VdtA is then O-methylated on C7 by the O-methyltransferase VdtC. The O-methyl group is important for the stereoselective coupling of the monomers at the final step of viriditoxin biosynthesis (PubMed:31304040). The short-chain dehydrogenase/reductase VdtF is involved in the reduction of the C3-C4 double bond (PubMed:31304040). The FAD-binding monooxygenase VdtE then converts the ketone group into a methyl-ester group to yield semi-viriditoxin (PubMed:31304040). Finally, the laccase VdtB is involved in dimerization of 2 semi-viriditoxin molecules to yield the final viriditoxin. The non-catalytic carboxylesterase-like protein VdtD affects the stereochemistical outcome of the coupling (PubMed:31304040). The highly reducing polyketide synthase VdtX is not involved in viriditoxin synthesis, but might possibly play a role in the production of additional metabolites not identified yet (PubMed:31304040). Multidomain protein; including a ketosynthase (KS) that catalyzes repeated decarboxylative condensation to elongate the polyketide backbone; a malonyl-CoA:ACP transacylase (MAT) that selects and transfers the extender unit malonyl-CoA; a dehydratase (DH) domain that reduces hydroxyl groups to enoyl groups; a methyltransferase (CMeT) domain responsible for the incorporation of methyl groups; an enoylreductase (ER) domain that reduces enoyl groups to alkyl group; a ketoreductase (KR) domain that catalyzes beta-ketoreduction steps; and an acyl-carrier protein (ACP) that serves as the tether of the growing and completed polyketide via its phosphopantetheinyl arm. Does not affect the production of viriditoxin.