METABOLIC PRODUCTS 283 



cate) —> succinate —> fumarate (Thunberg-Wieland condensation). R. 

 nigricans produces high yields of fumaric acid from both ethyl alcohol 

 and acetic acid, which is evidence in favor of this scheme of formation 

 (Foster and Waksman, 1939). 



Other organic acids. Apparently, the first organic acid to be dis- 

 covered as a product of fungus metabolism was oxalic acid. Many fungi 

 in nature contain calcium oxalate crystals. This was noted as early as 

 1887 by De Bary. Many species of Aspergillus and Penicillium produce 

 large amounts of oxalic acid, especially if enough alkali is present in the 

 medium to convert the acid into an oxalate. Many species of Aspergillus 

 which produce oxalate in the presence of a neutralizing agent also produce 

 citric acid in acid media (Currie, 1917). For a recent discussion of oxalic 

 acid production by fungi see Foster (1949). 



Various species of Aspergillus, including .4. oryzae, A. flavus, A. nidu- 

 lans, A. giganteus, and some other fungi produce kojic acid. Kojic acid 

 is a cyclic compound, a pyrone, and has been shown to have antibiotic 

 properties (Morton et al., 1945). 



ESTERS 



Among the esters reported to be formed by fungi are ethyl acetate, 

 methyl cinnamate, methyl p-methoxycinnamate, and isobutyl acetate. 

 Various reports are in the literature concerning a "banana-oil" odor 

 being produced by fungi, but apparently amyl acetate has not been 

 isolated and identified as a product of fungus metabolism. Ethyl acetate 

 is produced by Penicillium digitatum (Birkinshaw et al., 1931) and by 

 Endoconidiophora moniliformis (Gordon, 1950). 



ANTIBIOTICS AND DRUGS 



The inhibition of one organism by another is called antagonism. The 

 phenomenon has been known since the time of Pasteur, and the subject 

 has been reviewed by Waksman (1947) in a book containing over 1,000 

 references. Antagonism occurs in nature as well as in the laboratory 

 and is of such common occurence that it is frequently overlooked. Exam- 

 ples are easily found by examining contaminated plates for clear areas 

 around the contaminants. Antagonism may be due to competition for 

 nutrients or to toxic substances. This discussion will deal wdth the toxic 

 substances produced by fungi which inhibit fungi and bacteria. 



General discussion. Fungi and other organisms produce a variety 

 of toxic substances, which include enzymes, alkaloids, toxins, simple and 

 complex organic compounds, and inorganic compounds. Organic com- 

 pounds produced by fungi and other organisms, especially bacteria and 

 actinomycetes, which inhibit the life processes of microorganisms are 

 called antibiotics. Waksman (1947) would restrict the term antibiotic 



