THE formation of citric acid in plants and its probable participation in certain phytochemical alkaloid syntheses [cf.Robinson, 1917], together with the facts relating to its production and degradation by various species of Aspergillus and Penicillium, render of interest the study of its behaviour when submitted to the action of biological agents.Several investigations of the actions of various micro-organisms on citric acid and on citrates have been undertaken already; thus Bosworth and Prucha [1911] detected butyric and succinic acids together with hydrogen, carbon dioxide, and ethyl alcohol amongst the products of bacterial action on this acid.They also stated, without giving details, that two equivalents of acetic acid are produced from one equivalent of citric acid by B. lactis aerogenes.Terada [1924] fermented citric acid by a pure culture of an unclassified micro-organism isolated from an aerial infection, and obtained much succinic acid together with an appreciable quantity of acetic acid and a little aconitic acid.In the course of a quantitative investi- gation of the action of B. coli communis on various organic acids in the presence of formates, Grey [1924] found that cultures on citric acid gave rise to two equivalents of acetic acid together with some succinic acid and carbon dioxide.Brown, Duncan and Henry [1924] fermented trisodium citrate by B. suipestifer in the presence of peptone and concluded that the sole volatile acid formed was acetic acid (two equivalents) whilst the other products were carbon dioxide and a trace of succinic acid.During a recent examination of the action of Aspergillus niger on citric acid, Challenger, Subramaniam and Walker [1927] were able to demonstrate the formation of a number of substances, including acetone and malonic acid, which, hitherto, had not been identified amongst the products of mycological degradations of citric acid.It appeared of interest, therefore, to endeavour to ascertain whether the formation of these substances from citric acid by the action of A. niger is to be regarded as specific to this organism.For the purposes of this enquiry B. pyocyaneus was selected, since it may be grown very readily in media in which certain salts of citric acid constitute
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Butterworth et al. (1929) studied this question.