Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 10, 1999
Publication Date: N/A
Technical Abstract: The genus Chaetomium was targeted as a potentially rich source of antiinsectan natural products because different Chaetomium species have been shown to be avoided by or harmful to fungus- feeding insects. Chaetomium globosum is recognized for its biocontrol potential in crop protection against fungal plant pathogens. Only recently, however, has experimental evidence been offered to show that chetomin is the chemical basis for this observed antagonism. Bioassay guided studies using both antiinsectan assays (Helicoverpa zea) and antifungal assays (Aspergillus flavus) led us to a variety of known Chaetomium metabolites (i.e., antibiotic 1233A; chaetochromins; chaetoglobosin A, B, D, and F; 19-O-acetylchaetoglobosin A and D; chaetoviridins A, B, and X; chetocin; chetomin; dethiotetra (methylthio)chetomin; cochliodinol, cyclosporin A and C; eugenitin; sterigmatocystin; O-methylsterigmatocystin). Two novel compounds closely related to cytochalasins but with previously undescribed ring systems were discovered to have antiinsectan activity. One of these compounds was chaetochalasin A from Chaetomium brasiliense NRRL 22999, a culture isolated from a sclerotium of Aspergillus flavus that we buried in a corn field near Tifton, Georgia, USA. Among the compounds isolated in this work, only cyclosporin A and sterigmatocystin had been previously reported to have toxicity to insects. Most of these compounds were originally isolated as mycotoxins. The study confirmed our hypothesis that Chaetomium spp. produce potent insecticides as chemical defenses.