VOL. 12 (1953) 



CO2 TURNOVER IN FERMENTATION 



215 



succinate to propionate and COg, (3) there is a mechanism for randomization of the 2 and 

 3 positions of propionate, and (4) there is evidence that a C^ other than COg may be 

 formed in the conversion of succinate to propionate. It is apparent that further study 

 is required before it is possible to determine whether or not propionate can be formed 

 without involvement of a C4-dicarboxylic acid. 



The CO 2 turnover studies with erythritol and adonitol are of additional interest 

 as related to the mechanism of fermentation of 4 and 5 carbon compounds. The results 

 in Table VI indicate that extensive formation of exchangeable CO 2 is not a characteristic 

 of these fermentations. Furthermore, judging from the distribution of the fixed ^'^COg, 

 in the products, these fermentations do not involve CO 2 fixation mechanisms which 

 differ from those occurring during dissimilation of Cg and C3 compounds. This is shown 

 in Table VII in which the fixed ^^COg is confined almost entirely to carboxyl groups 



TABLE VII 



14, 



DISTRIBUTION OF FIXED ^'COg IN THE PRODUCTS OF FERMENTATION BY CULTURE 34W 



* The acetate was degraded and found to contain 0.058 cpmjfxM in the carboxyl group and 0.053 

 cpmlfiM in the methyl group. The counting was done on a flow counter and was at a level of 8 and 

 7 cts. above background. The background count was 24. 



Fermentation 16 was similar to Fermentation 14, see Table III. 



Fermentation 25 is described in Table IX. 



just as found previously with C3 and Cg substrates. Thus the CO2 turnover and CO2 

 fixation studies provide no definite clues as to the mechanism of these interesting fer- 

 mentations. Further speculation does not seem profitable at present although it is 

 attractive to consider that C^ compounds such as formaldehyde may play a role in these 

 fermentations^^'^^'^'*. 



Conditions necessary for extensive CO 2 fixation in glycerol fermentations. It is apparent 

 that the fixation of CO2 as reported in the experiments of Table III was far less than in 

 those presented in Table II. Different species of bacteria were used and it seemed 

 possible that this was the cause of the variation. A further difference was the method of 

 growing the cells. The cells used in Table III were cultivated by a special regime with 

 polyhydric alcohols as substrates. This was done in order to obtain cells which were 

 quite active on all four substrates, glycerol, erythritol, adonitol, and mannitol. On the 

 other hand the cells used in Table II were grown on a glycerol-phosphate-yeast extract 

 medium^. It has previously been found^ that the ability to fix CO 2 is markedly in- 

 fluenced by the composition of the growth medium and by far the best results were 

 obtained using the latter medium. 



It seemed advisable to determine if fixation of ^^COg during glycerol fermentation 

 similar to those previously reported^-^ could again be obtained. A number of preliminary 

 tests were run with bacteria grown on the glycerol-phosphate-yeast extract medium 



References p. 221I222. 



