METABOLIC PRODUCTS 295 



citrinin, are antibiotics. The physiological activity of solanione, a purple 

 pigment produced by Fusarium solani, decreases growth and the efficiency 

 of fat formation by F. lini (Weiss and Nord, 1949). Solanione is a 

 1,4-naphthoquinone, and this activity is in accord with the effects of other 

 compounds of this series. F. graminearum synthesizes an orange-red 

 pigment, rubofusarin, Avhich is a xanthone (Ashley et at., 1937). Rubo- 

 fusarin was found to stimulate growth and to inhibit the enzymatic 

 dehydrogenation of isopropyl alcohol by F. lini (Sciarini et al., 1943). It 

 is suggestive that pigment production frequently occurs near the time of 

 maximum development of mycelium. Perhaps pigments influence 

 sporulation in some way. 



Carotene is produced by Mucor hiemalis and Phycomyces blakesleeanus, 

 and probably by Mucor mucedo, Pilairia anomala, and Dicranophora fulva 

 (Schopfer, 1935). The amount of carotene produced by Phycomyces 

 blakesleeanus was increased by increasing the concentration of asparagine 

 in the medium. The plus strain of this fungus synthesized more carotene 

 than the minus strain. Carotene occurs in nature as three isomeric 

 compounds, all of w'hich may be converted into vitamin A. The carotene 

 found in M. hiemalis and P. blakesleeanus is ;S-carotene. Emerson and 

 Fox (1940) found 7-carotene to be associated with the male gametangia 

 of a certain species of Allomyces. Apparently carotene is also common 

 among the yellow or orange Ascomycetes and Basidiomycetes. 



SUMMARY 



The saprophytic fungi play an important, if not indispensable, part 

 in the degradation and decay of plant and animal residues. The most 

 important product of fungus metabolism in nature is carbon dioxide. 

 Humus is in part a result of the activities of soil-inhabiting fungi. 



Various species of fungi have been used for the preparation of food and 

 beverages. Fungi may be used to increase the world's supply of food. 

 Yeasts and other fungi are able to convert w-aste carbohydrate and 

 inorganic nitrogen compounds into protein, fats, and vitamins. Yeast 

 protein, because of its content of essential amino acids, has value as a 

 protein supplement. 



Alcoholic fermentation is not restricted to the yeasts, although these 

 fungi are used almost exclusively in industrj^ for this purpose. The 

 production of alcohol requires anaerobic or partially anaerobic conditions. 



Fungi may be used to produce organic acids, of which citric acid is the 

 most important commercially. In general, a medium high in carbo- 

 hydrate and low in nitrogen favors the production of organic acids, which 

 are synthesized in quantity only after growth is essentially complete. 



In nature one organism may be antagonistic to another because of the 

 competition for nutrients or because of the production of antibiotics. 



