Decarboxylase; part of the gene cluster that mediates the biosynthesis of orsellinic acid, as well as of the cathepsin K inhibitors F9775 A and F9775 B (PubMed:19666480, PubMed:20174687). The non-reducing polyketide synthase orsA produces orsellinic acid by condensing acetyl-CoA with 3 malonyl-CoA units (PubMed:19666480, PubMed:20174687). Further modifications by the decarboxylase orsB and the tyrosinase-like protein orsC lead to the production of F9775 A and F9775 B (PubMed:20174687). The functions of orsD and orsE remain unclear since only orsB and orsC are required to convert orsellinic acid into F9775 A and F9775 B (PubMed:20174687). Secondary metabolite biosynthesis. Expression is induced by an intimate physical interaction of the fungal mycelia with the bacterium Streptomyces hygroscopicus (PubMed:19666480). Expression is repressed by VeA and MvlA via histone 3 acetylation by the SAGA/ADA complex (PubMed:23892751, PubMed:23841751). Fails to produce F9775 A and B, but accumulates gerfelin and continues to yield orsellinic acid (PubMed:20174687). Belongs to the metallo-dependent hydrolases superfamily. ACMSD family.