384 METABOLISM OF MICROORGANISMS 



Butyric acid, butyl alcohol, and acetone all appear to arise from con- 

 densation of acetic acid by way of acetoacetic acid. 



CH.3 • COOH + CH3 • COOH -^ CH3 • CO • CHo • COOH + HoO 

 CH3 • CO • CHo • COOH + 4H ^ CH3 • CHo • CHo • COOH + HoO 

 CH3 • CHo • CHo • COOH + 4H -> CH3 • CHo • CHo • CH2OH 

 CH3 • CO • CHo • COOH -^ CH3 • CO • CH3 + COo 



The hydrogen for these reductions probably comes from the oxidative 

 steps in the glycolysis scheme that lead to pyruvic acid. There is also 

 hydrogen available from the breakdown of pyruvic acid to acetyl phos- 

 phate and carbon dioxide. 



CH3 • CO • COOH + H3PO4 -> CH3 • CO • • PO3H2 + CO2 + Ha 



Methane arises, in part at least, by reduction of carbon dioxide with 

 hydrogen : 



CO2 + 4H2 -^ CH4 + 2HoO 



A puzzling situation exists in respect to conversion of acetic acid to 

 methane. Isotope studies show that the methyl carbon, represented by 

 (*), is found in the methane, and the carboxyl carbon, indicated by 

 (**), appears in the carbon dioxide; hence methane, in this case, 

 does not arise by reduction of carbon dioxide by hydrogen. The direct 



C*H3C**00H -^ C*H4 + C**02 



decarboxylation as shown in the above equation is probably not the 

 actual mechanism. 



REVIEW QUESTIONS ON METABOLISM OF MICROORGANISMS 



1. Name some present-day foods that are the result of fermentation processes. 

 Name the class of microorganisms involved in each case. 



2. Define the terms "baker's yeast," "press yeast," "active dry yeast." What is 

 the scientific name for these types of yeast? Are any other species of yeast pro- 

 duced commercially? (Consult Chemical Abstracts for references to some of these 

 questions.) 



3. Give the major and minor products in alcoholic fermentation of glucose. How 

 can the ratio of the products be varied? 



4. Make a table of all the microorganisms listed in this chapter, the products 

 formed by them from sugar, and, where given, the percentage of sugar recovered 

 as product. 



5. Compare the fermentation of glucose by yeast with the metabolism of glucose 

 in the animal body. Give similarities and differences. 



6. What determines whether yeast or bacteria will develop in a food that is not 

 sterilized? For example, fmit juices undergo an alcoholic fermentation, whereas 

 milk becomes sour. Cabbage when shredded and packed into vats undergoes a 

 mixed lactic acid fermentation. (Consult a book on bacteriology.) 



7. What products, if any, would you expect to be formed by A. suhoxydans 

 from (1) glycerol, (2) dulcitol, (3) sorbitol, (4) 2,3-butylene glycol, (5) gluco.«e? 



