Sugars and amino acids as factors affecting the synthesis of fumonisins in liquid cultures by isolates of the Gibberella fujikuroi complex

The capacity of four isolates belonging to the Gibberella fujikuroi complex to produce fumonisin B1 and fumonisin B2 when grown in liquid medium supplemented with one sugar and one amino acid at various concentration levels has been investigated. The sugars used for supplementing the medium were glucose, fructose, rhamnose, sucrose, maltose, and trehalose at 5, 10 or 20 g/l. The amino acids used were serine, threonine, glutamic acid, aspartic acid, valine, isoleucine, methionine, glycine, alanine, and cystine at 1 or 10 g/l. Fumonisins were extracted from culture filtrates, purified by SAX column and determined by reversed-phase C18 HPLC with fluorescence detection of the o-phthaldialdehyde derivatives. Two isolates produced very low concentrations of fumonisins with all sugars. The remaining isolates provided increased contents of fumonisins when sugar level increased. Concerning the amino acids, production of fumonisins was also dependent on the isolate, although at 1 g/l, the production of fumonisins was greater than at 10 g/l. The results indicate that the sugar–amino acid-isolate combination is basic in fumonisin biosynthesis and that the particular behaviour of each isolate in the different nutritional conditions may constitute a piece of interesting information in the fields of the Taxonomy, Physiology and Toxicology of these fungi. This is the first report on the influence of the carbon and nitrogen sources on fumonisin production by isolates of the G. fujikuroi complex.