METABOLISM OF MICROORGANISMS 363 



others. Lactic acid, for example, is produced by many bacteria, but 

 only a few molds make it, and yeasts produce it only in traces or under 

 special conditions. 



Products that are limited to bacteria are hydrogen, the lower fatty 

 acids, butylene glycol, butyl alcohol, acetone, and isopropyl alcohol. 

 Several of these products are closely related, as will be shown later. 



Di- and tri-basic acids are characteristic of molds. Succinic acid is 

 the only one of this type common to all three groups. Although it has 

 been found in yeast fermentations, it appears to originate from oxida- 

 tion and decarboxylation of glutamic acid rather than from glucose. 



If a fourth column to include animals were tabulated, it would be 

 found to be mostly negative, except for carbon dioxide. Lactic acid, 

 acetic acid, and acetone are found at times in the urine, but they are 

 not normal end products of animal metabolism. 



The high yields obtained with some microorganisms have made possible 

 a number of industrial fermentations. The mechanism of the formation 

 of these products will be discussed later. 



Table 14-1 



Characteristic end products of carbohydrate metabolism formed by 

 bacteria, yeasts, and molds * 



Compound Bacteria Yeasts Molds 



Carbon dioxide CI. acetobutylicum, 55 S. cerevisiae, 45 P. chrysogenum, 70 



Lactic acid L. delbrilckii, 90 S. cerevisiae, trace R. oryzae, 75 



Ethyl alcohol T. mobile, 45 S. cerevisiae, 45 F. avenaceum, 40 



Acetic acid L. gayonii, 10 S. cerevisiae, 1-3 A. nigcr, trace 



Glycerol L. lycopersici, 20 S. cerevisiae, 1-40 Aspergillus sp., 10 



Mannitol L. gayonii, 65 None Aspergillus sp., 35 



Gluconic acid A. suboxydans, 95 None A.niger,95 



Propionic acid P. pentosaceum, 60 None ? 



Formic acid E. typhi, 10 None None 



Hydrogen E. coli, 0.5 None None 



Succinic acid E. coli, 12 Doubtful Rhizopus,sp., small 



Acetoin A. aerogenes, 0.5 Trace None 



Butylene glycol A. aerogenes, 45 ? None 



Butyric acid CI. saccharobutyricum. None None 



40 



Butyl alcohol CI. acetobutylicum, 2Q None None 



Acetone CI. acetobutylicum,, 7 None None 



Isopropyl alcohol . . . .CI. butylicum, 6 None None 



Oxalic acid None None A. niger, 80 



Fumaric acid None None R. nigricans, 60 



Citric acid None None A. niger, 90 



* The microorganisms named are typical of the best producers of the compounds. 

 The figures denote the maximum percentage of product, based on glucose or fructose 

 fermented, that has been found in the literature. The yield of product, usually less, 

 will vary with other substrates, microoi-ganisms, and fermentation conditions. 



