Organic acid production by Basidiomycetes. 3. 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 CaCO(3)-containing medium in shaken culture. The most favorable nitrogen sources selected were 0.3% (NH(4))(2)SO(4) and 0.18% NH(4)Cl. Effective combinations of inorganic salts in the medium were 0.1% KH(2)PO(4), 0.05% MgSO(4).7H(2)O, 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%.

Organic acid production by Basidiomycetes. I. Screening of acid-producing strains

Sixty-seven strains belonging to 47 species of Basidiomycetes were examined for their acid-producing abilities in glucose media, in both the presence and absence of CaCO(3), in stationary and shake cultures. Some strains were found to produce large quantities of oxalic acid. The oxalic acid-producing strains could be separated into two groups. Strains of one group (mostly brown-rot fungi) were able to produce oxalic acid, regardless of whether CaCO(3) was present in the medium. Strains of the other group (mostly white-rot fungi) were characterized by their ability to produce oxalic acid only when CaCO(3) was added to the medium. With the latter group, shake-culturing was generally more effective than stationary culturing in respect to acid production. In the CaCO(3)-containing media, Schizophyllum commune, Merulius tremellosus, and Porodisculus pendulus were found to produce substantial amounts of L-malic acid as a main metabolic product, along with small quantities of oxalic and other acids in shake cultures. Especially, S. commune and M. tremellosus may be employed as malic acid-producing species.