FAD-binding monooxygenase; part of the gene cluster that mediates the biosynthesis of calidodehydroaustin, a fungal meroterpenoid (PubMed:28233494, PubMed:29076725). The first step of the pathway is the synthesis of 3,5-dimethylorsellinic acid by the polyketide synthase ausA (PubMed:28233494). 3,5-dimethylorsellinic acid is then prenylated by the polyprenyl transferase ausN (PubMed:28233494). Further epoxidation by the FAD-dependent monooxygenase ausM and cyclization by the probable terpene cyclase ausL lead to the formation of protoaustinoid A (By similarity). Protoaustinoid A is then oxidized to spiro-lactone preaustinoid A3 by the combined action of the FAD-binding monooxygenases ausB and ausC, and the dioxygenase ausE (By similarity). Acid-catalyzed keto-rearrangement and ring contraction of the tetraketide portion of preaustinoid A3 by ausJ lead to the formation of preaustinoid A4 (By similarity). The aldo-keto reductase ausK, with the help of ausH, is involved in the next step by transforming preaustinoid A4 into isoaustinone which is in turn hydroxylated by the P450 monooxygenase ausI to form austinolide (By similarity). The cytochrome P450 monooxygenase ausG modifies austinolide to austinol (By similarity). Austinol is further acetylated to austin by the O-acetyltransferase ausP, which spontaneously changes to dehydroaustin (PubMed:28233494). The cytochrome P450 monooxygenase ausR then converts dehydroaustin is into 7-dehydrodehydroaustin (PubMed:28233494). The hydroxylation catalyzed by ausR permits the O-acetyltransferase ausQ to add an additional acetyl group to the molecule, leading to the formation of acetoxydehydroaustin (PubMed:28233494). The short chain dehydrogenase ausT catalyzes the reduction of the double bond present between carbon atoms 1 and 2 to convert 7-dehydrodehydroaustin into 1,2-dihydro-7-hydroxydehydroaustin (PubMed:28233494). AusQ catalyzes not only an acetylation reaction but also the addition of the PKS ausV diketide product to 1,2-dihydro-7-hydroxydehydroaustin, forming precalidodehydroaustin (PubMed:28233494). Finally, the iron/alpha-ketoglutarate-dependent dioxygenase converts precalidodehydroaustin into calidodehydroaustin (PubMed:28233494). AH2 + O2 + preaustinoid A = A + H2O + preaustinoid A1 Binds 1 FAD per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. In A.calidoustus, the austinoid gene cluster lies on a contiguous DNA region, while clusters from E.nidulans and P.brasilianum are split in their respective genomes. Genetic rearrangements provoked variability among the clusters and E.nidulans produces the least number of austionoid derivatives with the end products austinol and dehydroaustinol, while P.brasilianum can produce until acetoxydehydroaustin, and A.calidoustus produces the highest number of identified derivatives. Belongs to the FAD-binding monooxygenase family.