Assessing the Biosynthetic Potential of the Bioherbicide <i>Colletotrichum spinosum</i> CBS 515.97: Discovery of 3”‐Demethylthielavin M and Assorted Alkaloids

Colletotrichum spinosum has demonstrated potential as a bioherbicide against the invasive and noxious weed Xanthium spinosum. Here, we take a genome mining approach to uncover the biosynthetic potential of C. spinosum CBS 515.97 in parallel to the one strain many compounds approach for understanding which natural products are produced under lab conditions. The tridepside 3''-demethylthielavin M (1)_, two primary metabolites tryptophol (2) and anthranilic acid (3), five alkaloids including chrysogine (4) and the diketopiperazines (DKPs; 5-8), were isolated from the ethyl acetate extracts of C. spinosum and subject to full structural elucidation, including high-resolution electrospray ionization mass spectrometry, one- and two-dimensional nuclear magnetic resonance. The stereochemistry of the DKPs was determined by Marfey's method. In-depth bioinformatic analysis identified the putative biosynthetic gene cluster encoding 3''-demethylthielavin M (1), and a biosynthetic pathway is proposed. Biological testing of metabolites 1-8 on leaves of the model plant Nicotiana benthamiana indicated that 3''-demethylthielavin M (1) induced moderate effects, whereas tryptophol (2) induced more severe effects.