Mechanism of oxalic acid fermentation by Aspergillus niger

Oxalic acid is commonly found in spinach and in other vegetables and some microorganisms. Aspergillus niger produces large amounts of citric acid, and yields gluconic, fumaric and oxalic acids as by-products. As the expectable intermediates producing oxalic acid, pyruvate, citrate, glyoxylate or oxaloacetate was separately added to the growing mycelia of Aspergillus niger during fermentation, and the amount of oxalate was determined during cultivation. Oxalate was produced in all media tested, and was degraded later and a small amount of formate was present in the media. When oxalate was used as a substrate, it decreased, so that it was probably not an end product. Furthermore, it was confirmed that the cell-free extracts of the mycelia in the growth culture had enzyme activities which produced oxalate from both oxaloacetate and glyoxylate and degraded oxalate to formate. Oxalate seemed to be yielded via both oxaloacetate and elvoxvlate and that formate was an intermediate in the nathwav to oxalate deeradation.