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Secondary metabolites are chemical compounds, that are synthesized by fungi, bacteria and plants. In contrast to primary metabolites, secondary metabolites are not necessary for the sur- vival of an organism, but have advantages over other organisms. The secondary metabolites include microbial biosurfactants, which always show the same composition. They consist of a hy- drophilic and a hydrophobic part. This amphiphilic structure leads to the typical surface-active properties. In contrast to industrially produced surfactants, biosurfactants are biodegradable, non-toxic and heat-stable. Glycolipids are a group of biosurfactants. They consist of one or more sugars, which are decorated with hydroxy fatty acids. In the kindom of fungi many different glyco- lipids can be found, including ustilagic acid and mannosylerythritol lipids, which are synthesized by the phytopathogenic basidiomycete Ustilago maydis. These two glycolipids are synthesized under nitrogen starvation conditions. Ustilagic acid has a strong surface activity and shows an antibiotic effect against yeasts and Gram-positive bacteria. Besides the strong surface activity, the mannosylerythritol lipids also exhibit haemolytic activity. The biosynthesis pathways of these two glycolipids have already been well characterized.
During the screening of many different fungal isolates, two further basidiomycetes have been found, named Macalpinomyces eriachnes and Sporisorium scitamineum, which are also able to synthesize different variants of these glycolipids. The glycolipids produced by M. eriachnes are surface-active and have a hemolytic effect. S. scitamineum glycolipids are also surface-active and have an antibiotic effect towards yeasts. Besides these two phytopathogenic fungi, another unidentified fungus was found which is able to produce a sugar containing secondary metabolite. By sequencing, this black yeast was identified as Dothiora cannabinae. Under nitrogen starvation conditions, D. cannabinae is able to synthesize a glycolipid-like substance. By mass spectrometry analysis and nuclear magnetic resonance spectroscopy the substance was identified as glyco-oligo- hydroxy-alkanoate. This substance is surface active and shows haemolytic activity.
The hexadecanoic acid of the ustilagic acid is found in U. maydis in di- and trihydroxylated form. The hydroxylations are catalyzed by the two P450 monooxigenases Cyp1 and Cyp2. The overexpression of Cyp1 in a U. maydis strain, which does not synthesize ustilagic acid, results in a monohydroxylation of the hexadecanoic acid of the MELs. The overexpression of both P450 monooxigenases leads to a dihydroxylation of the hexadecanoic acid of the MELs. However, this modification of the MELs had no effect on the properties of this glycolipids.