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Formation of exudate droplets by Metarhizium anisopliae and the presence of destruxins

     Institute of Microbiology, University of Innsbruck, Innsbruck, Austria

Hui Wang ²

     College of Plant Protection, Northwest A&F University, YangLing 712100, Shaanxi, P.R. China

Hermann Strasser
Wolfgang Burgstaller

     Institute of Microbiology, University of Innsbruck, Innsbruck, Austria

Nutritional conditions causing droplet exudation by Metarhizium anisopliae var. anisopliae were studied. Exudation in droplets occurred only on media with more than one carbon source and was highly dependent on the ratio of a well metabolized sugar such as trehalose and a nonpreferred sugar, in particular arabinose. Exuded droplets contained destruxin A, B and E in concentrations similar to those on submerged culture on Czapek Dox medium with equivalent C : N ratios but was clearly less than previously reported on standard Czapek Dox or Sabouraud dextrose broth. Destruxins also were found in agar samples from directly below mycelium and from up to 2 cm from the colony edge. Exudates retrieved from different media were proven to have Pr1 protease-related enzyme activity. Additional HPLC analysis indicated that droplets from diverse media did not differ in their sugar and acid content. A hypothesis is presented regarding the trigger for guttation in Metarhizium during growth under these conditions.

Key words: arabinose, extrolites, fungal guttation, mycotoxins, pathogenic fungi, secondary metabolites