210 



H. G. WOOD, F. W. LEAVER 



VOL. 12 (1953) 



C4->2C2; 2C4 +2Ca— ^2C6 (i) 



2 C^ — '^ 4 C3 > products of fermentation 



The overall reaction is 3 C4 — -^ 2 Cg — ■-> 4 C3 — > products 



C4 — -^ 2 C2; 2 C4 — ~» 2 C3 + 2 Cii 2 C2 + 2 Ci — -^ 2 C3 (2) 



The overall reaction is 3 C4 > 4 C3 > products 



If the Ci in the second example were CO 2 it is evident that it could be distinguished 

 from the first mechanism by determination of the CO 2 turnover. 



TABLE IV 



RESULTS OF TABLE II EXPRESSED ON THE BASIS OF 30O mAI FERMENTED CARBON 



No. Substrate 



CO, 



Succinate 



Propionate 



Acetate 



Alcohol 



NRC 



Formate 



With adonital and arabinose a cleavage to C3 and C2 compounds may be involved. 

 The fermentation of pentose by Lactobacillus pentosus as investigated by Fred et al}^ 

 and more recently by the tracer technique by Gest and Lampen^^ and Bernstein^^ 

 is an example of such a cleavage. A similar cleavage has been investigated with Lacto- 

 bacillus arabinosum by Rappoport et al.^''. If such a cleavage occurs in the propionic 

 acid fermentation the C^ compounds must have been used in further conversion since 

 per 100 mM of adonital fermented there is far less than the expected 100 mil/ of C2 

 compounds. From the investigations of Akabori^^, Horecker^^, and Racker^" it has 

 become evident that erythrulose and sedoheptulose may be involved in the formation of 

 a C3 from the pentose. These studies indicate that the fermentation of pentose may 

 involve a rather complicated series of reactions. 



•i. 



turnover studies with ^*C02 



Present concepts of CO 2 turnover by the propionic acid bacteria are largely based 

 on the observations of Wood et al.^who obtained the following results from a fermentation 

 of glycerol expressed as atom per cent excess ^^C : Original CO2 = 3-55, final CO2 = 2.53, 

 COOH of propionate = 1.17 and COOH of succinate = 1.12. The ^^C of the carboxyl 

 groups of succinate and propionate though not equal to one-half that of the average 

 of the CO2 did approach the theoretical values as required for the scheme given in Fig. i. 



Erb^i and Werkman and Wood'^ (p. 151) found that succinate was dccarboxylated 

 by the propionic acid bacteria at pH 5.2 and propionate and CO2 were formed^, but 

 the reaction rate was slow. However, Delwiche^ and Johns' concluded from their 

 studies with these bacteria that propionate is most likely formed by this mechanism. At 

 acid pH the rate of decarboxylation of succinate was found to be comparable to the 

 rate of propionate formation. Barban and Ajl^^ have investigated the reversibihty 

 of the decarboxylation of succinate using resting cells of propionic bacteria, ^''COg, 

 succinate, fumarate and malate. It was fotmd that the succinate was labelled but not the 



p. 221I222. 



