title: Genetic analysis of biosurfactant production in Ustilago maydis.
abstract: The dimorphic basidiomycete Ustilago maydis produces large amounts of surface-active compounds under conditions of nitrogen starvation. These biosurfactants consist of derivatives of two classes of amphipathic glycolipids. Ustilagic acids are cellobiose lipids in which the disaccharide is O-glycosidically linked to 15,16-dihydroxyhexadecanoic acid. Ustilipids are mannosylerythritol lipids derived from acylated beta-d-mannopyranosyl-d-erythritol. Whereas the chemical structure of these biosurfactants has been determined, the genetic basis for their biosynthesis and regulation is largely unknown. Here we report the first identification of two genes, emt1 and cyp1, that are essential for the production of fungal extracellular glycolipids. emt1 is required for mannosylerythritol lipid production and codes for a protein with similarity to prokaryotic glycosyltransferases involved in the biosynthesis of macrolide antibiotics. We suggest that Emt1 catalyzes the synthesis of mannosyl-d-erythritol by transfer of GDP-mannose. Deletion of the gene cyp1 resulted in complete loss of ustilagic acid production. Cyp1 encodes a cytochrome P450 monooxygenase which is highly related to a family of plant fatty acid hydroxylases. Therefore we assume that Cyp1 is directly involved in the biosynthesis of the unusual 15,16-dihydroxyhexadecanoic acid. We could show that mannosylerythritol lipid production is responsible for hemolytic activity on blood agar, whereas ustilagic acid secretion is required for long-range pheromone recognition. The mutants described here allow for the first time a genetic analysis of glycolipid production in fungi.
authors.affiliation: Philipps-Universität Marburg, Fachbereich Biologie, 35032 Marburg, Germany. marburg.de.
authors.forename: Sandra
authors.initials: S
authors.lastname: Hewald
authors.forename: Katharina
authors.initials: K
authors.lastname: Josephs
authors.forename: Michael
authors.initials: M
authors.lastname: Bölker
mesh_terms: D000595:Amino Acid Sequence; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D006017:Glycolipids / Q000096:biosynthesis*; D016695:Glycosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006461:Hemolysis; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D016415:Sequence Alignment; D013501:Surface-Active Agents / Q000378:metabolism*; D014588:Ustilago / Q000235:genetics* / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D006017:Glycolipids; D013501:Surface-Active Agents; C439671:mannosylerythritol lipid; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D016695:Glycosyltransferases