Organic Acid Production by Basidiomycetes III. Cultural Conditions for L-Malic Acid Production

Cultural conditions were examined for the purpose of increasing yields of l-malic acid by the Basidiomycetes Schizophyllum commune and Merulius tremellosus, which have the ability to produce this acid as a main product in CaCO3-containing medium in shaken culture. The most favorable nitrogen sources selected were 0.3% (NH4)2SO4 and 0.18% NH4Cl. Effective combinations of inorganic salts in the medium were 0.1% KH2PO4, 0.05% MgSO4·7H2O, and 0.05% KCl, and suitable concentrations of glucose were 5 to 10%. Several nonionic surface-active agents promoted the filamentous mycelial growth of these strains and increased acid production. In particular, Tween 80 in 0.3% concentration markedly stimulated malic acid production by S. commune, and yields greater than 50% based on available glucose, were obtained after 10 to 14 days. Acid production by M. tremellosus was stimulated most with 0.5% Carbowax 4000 (polyethylene glycol), and the resultant yields were more than 40%.