Metabolite diversity in the plant pathogen Alternaria brassicicola: factors affecting production of brassicicolin A, depudecin, phomapyrone A and other metabolites

Abstract

A systematic investigation of the metabolites of Alternaria brassicicola produced under various culture conditions is reported. The phytotoxin brassicicolin A is produced in significantly larger amounts in potato dextrose broth than in minimal medium cultures. In general an increase in the incubation temperature of cultures 23–30 C increases the production of brassicicolin A but decreases depudecin production. Reducing or eliminating nitrate from culture media or adding ammonium chloride increases the production of brassicicolin A at 30 C, depudecin at 23 C and α-acetylorcinol at either temperature, suggesting that nitrogen represses their biosynthesis. Siderophores are detected in cultures of A. brassicicola containing low and high ferric ion concentrations. The metabolites α-acetylorcinol and tyrosol are isolated for the first time from cultures of A. brassicicola, and α-acetylorcinol is synthesized in four steps and 36% overall yield. Only brassicicolin A and no other isolated metabolites, including depudecin and phomapyrone A, display phytotoxicity on leaves of Brassica species (up to 5.0 mM). Epigenetic modifiers, 5-azacitidin (5-AZA), suberoylanilide hydroxamic acid (SAHA) and suberoyl bis-hydroxamic acid (SBHA) do not affect the metabolite profiles of liquid cultures of this fungal pathogen.

• α-acetylorcinol
• HDAC inhibitors
• host-selective
• phytotoxin
• siderophores
• tyrosol

Acknowledgments

We thank K. Thoms from Chemistry and SSSC for HRMS-ESI and HRMS-EI data. Financial support for this work was obtained from the Natural Sciences and Engineering Research Council of Canada (Discovery Grant to MSCP), the Canada Research Chairs program, Canada Foundation for Innovation, as well as the University of Saskatchewan for a dean’s scholarship and teaching assistantship to MRP.