FAD-dependent monooxygenase; part of the gene cluster that produces the tetronate natural products trihazones (PubMed:33570538). Transcription analysis of thnD confirmed this gene is expressed, hence its role in the biosynthetic pathway remains cryptic (PubMed:33570538). The pathway begins with the formation of trihazone A by the hybrid PKS-NRPS synthetase thnA and the trans-enoyl reductase thnE. Trihazone A is further decarboxylated by the 2-oxoglutarate-dependent dioxygenase thnC to produce trihazone D. The function of the FAD-dependent monooxygenase thnD has still to be identified (PubMed:33570538). Belongs to the paxM FAD-dependent monooxygenase family.