Many fungi in the Stachybotrys genus can produce various isoindolinone derivatives. These compounds are formed by a spontaneous reaction between a phthalic aldehyde precursor and an ammonium ion or amino compounds. In this study, we suggested the isoindolinone biosynthetic gene cluster in Stachybotrys by genome mining based on three reported core genes. Remarkably, there is an additional nitrate reductase (NR) gene copy in the proposed cluster. NR is the rate-limiting enzyme of nitrate reduction. Accordingly, this cluster was speculated to play a role in the balance of ammonium ion concentration in Stachybotrys. Ammonium ions can be replaced by different amino compounds to create structural diversity in the biosynthetic process of isoindolinone. We tested a rational supply of amino compounds ((±)-3-amino-2-piperidinone, glycine, and l-threonine) in the culture of an isoindolinone high-producing marine fungus, Stachybotrys longispora FG216. As a result, we obtained four new kinds of isoindolinone derivatives (FGFC4-GFC7) by this method. Furthermore, high yields of FGFC4-FGFC7 confirmed the outstanding production capacity of FG216. Among the four new isoindolinone derivatives, FGFC6 and FGFC7 showed promising fibrinolytic activities. The knowledge of biosynthesis pathways may be an important attribute for the discovery of novel bioactive marine natural products.
Keywords: Stachybotrys; amino compound; fibrinolytic activity; genome mining; isoindolinone biosynthesis.