Catabolism of flocculosin, an antimicrobial metabolite produced by Pseudozyma flocculosa

Flocculosin is an unusual cellobiose lipid secreted by the yeast-like fungus Pseudozyma flocculosa as part of its biocontrol arsenal against other fungi. Recent observations have suggested that the fungus degrades flocculosin to use it as a nutrient source during periods of food limitation. In this work, we sought to identify the catabolic steps leading to the degradation of flocculosin and its subsequent use by P. flocculosa. To this end, we characterized the catabolism of flocculosin through identification of degradation intermediates in a deprived medium using mass spectrometry. As the pH of the medium increased, the molecule was quickly deacylated and lost its antimicrobial activity thereby explaining conflicting results concerning the antimicrobial activity of this class of glycolipid. Following removal of both acetyl groups and the short fatty acid chain under alkaline conditions, the molecule was quickly and completely metabolized by P. flocculosa. Protein purification of culture filtrates confirmed the presence of degradative enzymes produced by P. flocculosa. These enzymes were found to degrade 3,15-dihydroxy-hexadecyl cellobioside (DHC) but not the acylated molecule, thus confirming the protective role of these groups against catabolism. These results are the first evidence of glycolipid degradation by producing organism and suggest that flocculosin can be recycled by P. flocculosa as a nutrient in addition to protecting its ecological niche.