Non-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, PubMed:31045362). 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 (PubMed:31304040, PubMed:31045362). The O-methyl group is important for the stereoselective coupling of the monomers at the final step of viriditoxin biosynthesis (PubMed:31304040, PubMed:31045362). The short-chain dehydrogenase/reductase VdtF then acts as a stereospecific reductase converting the pyrone to dihydropyrone via the reduction of the C3-C4 double bond (PubMed:31304040, PubMed:31045362). The FAD-binding monooxygenase VdtE then converts the ketone group into a methyl-ester group to yield semi-viriditoxin (PubMed:31304040, PubMed:31045362). Finally, the laccase VdtB is involved in dimerization of 2 semi-viriditoxin molecules to yield the final viriditoxin (PubMed:31304040, PubMed:31045362). VdtB is responsible for the regioselective 6,6'-coupling of semi-viriditoxin, which yields (M)-viriditoxin and (P)-viriditoxin at a ratio of 1:2 (PubMed:31304040, PubMed:31045362). The non-catalytic carboxylesterase-like protein VdtD affects the stereochemistical outcome of the coupling (PubMed:31304040, PubMed:31045362). 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, PubMed:31045362). acetyl-CoA + 7 H(+) + 7 malonyl-CoA = 7,9,10-trihydroxy-3-(2-oxopropyl)-1H-benzo[g]isochromen-1-one + 7 CO2 + 8 CoA + 2 H2O Secondary metabolite biosynthesis. The vesicles where VdtA is targeted remain unknown. Multidomain protein; including a starter unit:ACP transacylase (SAT) that selects the starter unit; 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 product template (PT) domain that controls the immediate cyclization regioselectivity of the reactive polyketide backbone; and 3 acyl-carrier protein (ACP) domains that serve as the tether of the growing and completed polyketide via its phosphopantetheinyl arm. Abolishes the production of viriditoxin.