34 RAPER 



bacteria to produce solvents had been reported, and the retting of plant 

 tissues by related microorganisms to release valuable fibers was reasonably 

 well understood. In the Orient, certain molds in association with yeasts and 

 bacteria were propagated empirically for the production of soy sauce and 

 other fermented foods. 



Nevertheless, the primary emphasis in microbiology, particularly with ref- 

 erence to the bacteria, had been directed principally toward isolating them 

 and elucidating their roles in the disease processes of man, his domestic ani- 

 mals, and his cultivated plants. Thus germs, as they had come to be known, 

 were generally regarded as vicious, if miniscule, enemies to be combated at all 

 costs. There was, of course, ample cause for such concern. Whereas this phase 

 of microbiology has not become less important during the past fifty years and 

 continued efforts and the application of techniques then unknown must be 

 used unrelentingly to hold disease-producing microbes in check, there has 

 developed parallel with it a broad and expanding area of research and tech- 

 nological application directed toward the utilization of microorganisms for 

 constructive ends. I shall direct my attention to this latter development. It 

 is not possible in a brief paper to encompass the whole field of present-day 

 applied microbiology, and I must seek the reader's indulgence as I select, 

 somewhat arbitrarily, certain areas for consideration. 



THE PRODUCTION OF ORGANIC ACIDS 



The microbiological production of organic acids represents one of the older 

 and one of the more productive of these areas — productive not only for the 

 variety of acids that can now be manufactured biosynthetically, but equally 

 important for the background of accumulated information that made possible 

 the large-scale production of antibiotics and other microbial products of more 

 recent date. As early as 1867 the French mycologist van Tieghem demon- 

 strated that the tannin contained in gall nuts was converted to gallic acid 

 by the action of a common saprophytic mold Sterigmatocystis nigra {Aspergil- 

 lus niger). By present standards, the fermentation as conducted was quite 

 empirical, for it consisted merely of piling the substrate into mounds and 

 periodically turning these inside out to provide aeration and thus facilitate 

 the growth of the fungus, following which the acid was recovered by leaching. 

 It is interesting to note that this acid is still produced by mold fermentation, 

 although other tannin-rich materials are now utilized as substrates and the 

 responsible enzyme, tannase, is often freed from the mold prior to being 

 used as the converting agent. The current production of this acid is not large, 

 but it finds important industrial uses in the manufacture of inks and dyes 

 and in the formulation of pharmaceuticals for the treatment of burns. It com- 

 mands a price of ca. $2.00 per pound. 



The mycological production of citric acid represents the next oldest and 



