THE FORMATION OF OXALIC ACID BY ASPERGILLUS NIGER

Abstract

CERTAIN strains of A spergillus niger produce large quantities of oxalic acid in the presence of a wide variety of organic substrates. The formation of oxalic acid by A. niger was first investigated by Wehmer (I89I a, b), but he made no attempt to explain the chemical nature of the changes involved. At the present day, despite the attention of many workers, there is still surprisingly little exact knowledge of the chemistry of the process. Almost all research on the mechanism of the conversion of glucose into oxalic acid has been based on feeding experiments, in which it is assumed that if the substance under investigation is a member of the normal sequence of reactions it should yield oxalic acid at least as quickly as glucose. Failure to obtain oxalic acid is taken to indicate that the substance supplied plays no part as an intermediate product. The most noteworthy work of this type was carried out by Raistrick & Clark (I9I9), who grew A. niger on culture solutions containing salts of various organic acids. After the lapse of about 5 weeks it was found that oxalic acid had been produced in quantity from the salts of malic, tartaric, succinic, fumaric, and acetic acids. The case of lactic acid was outstanding for, although growth was heavier than in any other instance, no oxalic acid was detected. From the fact that oxalic acid was not obtained from the salts of the 3-carbon acids, Raistrick & Clark concluded that glucose degradation does not follow the Neuberg reactions in A spergillus. They held the view that i molecule of glucose gives rise to i molecule each of oxalacetic acid and acetic acid. The oxalacetic acid is said to be hydrolysed into oxalic and acetic acid, and both molecules of acetic acid arising from the glucose are believed to undergo further oxidation to oxalic acid. This hypothesis, according to which oxalacetic acid is the immediate precursor of oxalic acid, has the advantage of