Differences of Rhizopus oryzae strains in organic acid synthesis and fatty acid composition

Two groups of 15 Rhizopus oryzae strains were grown in a liquid medium to analyse metabolic products such as lactic, fumaric, malic and other organic acids and ethanol. Group A produced a large amount of lactic acid, while group B produced a small amount. The addition of calcium carbonate to the medium of group A stimulated the production of lactic acid, but not fumaric and malic acids. As compared with group A, organic acids were only slightly synthesized in group B. Fumaric and malic acids appeared in the medium of group B, which was supplemented with calcium carbonate, but lactic acid was not detected. Myristic, palmitic, palmitoleic, oleic, stearic, linoleic and γ-linolenic acids were determined for total lipids extracted from the fungal cells and subjected to principal component analysis. Group A contained high amounts of unsaturated fatty acids and differed from group B in the proportion of palmitic and γ-linolenic acids. The content of γ-linolenic acid increased by the addition of lactic acid to the medium and not by those of ethanol and NaCl. The physiological differences in R. oryzae strains may depend on the productivity of organic acids, reflecting the composition of fatty acids.