VOL. 12 (1953) CO2 TURNOVER IN FERMENTATION 209 



were done several years ago, those in Table III are from experiments using ^^COg and 

 were set up under conditions suitable for measurement of CO 2 turnover. The fermenta- 

 tions in Table I were with proliferating cells but in all other fermentations resting cells 

 were used. Arabinose was included as representative of a pentose and galactose of a 

 hexose which had not been previously studied. 



The most noteworthy aspect of the results shown in these tables is that no matter 

 what the length of the carbon chain of the substrate the products are identical and the 

 amounts are very similar. This point is shown more clearly in Table IV in which the 

 results are expressed on the basis of 300 mM of fermented carbon, i.e., equivalent to 

 100 mM of 3-carbon compounds. The level of oxidation or reduction of the substrate, 

 of course, has an effect on the amounts of products in an anaerobic fermentation. Thus 

 glycerol and pyruvate yield a different ratio of products (Table III) ; the fermentation 



TABLE III 



FERMENTATION OF 3, 4 AND 5 CARBON SUBSTRATES BY WASHED CELLS OF P. aVabinOSUm, 34W 



* Formate has not been reported as a product of the propionic acid fermentation but it was found 

 in significant amount - especially from erythritol, see also Table II. 



* * The alcohol was not identified and the values are the volatile acid resulting from oxidation of 

 the neutral distillate. Wood and Werkman^* have identified propyl alcohol as a product of glycerol 

 fermentation and the balances are calculated on the basis that the alcohol is propyl alcohol. 



100 ml of mixture in a i liter flask under Ng at 20 to 30 cm Hg; o.i M substrate, 0.3 M K-phos- 

 phate buffer at pH 7.0, 5% wet cells, NaHi^COj o.oi to 0.03 M {cf. Table VI). Temperature 30° C. 

 Time 43 h except for glycerol 20 h. The bacteria were from 3 days growth on 0.3 % glycerol, 0.05 % 

 i-erythritol, 0.05 % ^-mannitol, 0.05 % 6?-adonitol, 0.5 % yeast extract and o.oi M K-phosphate 

 buffer at pH 7.0. The inoculum for the above medium was grown on 0.3% z-erythritol, 0.05% d- 

 mannitol, 0.05% li-adonitol, 0.005% glucose, 0.5% yeast and o.oi M phosphate buffer at pH 7.0. 

 Methods were as described in text. 



of pyruvate results in more COg and less of the reduced product propionate than the 

 fermentation of glycerol. In general the more reduced the substrate the greater was the 

 utilization of COg. 



The fact that the products of the 3, 4, 5, and 6 carbon compounds are identical 

 and the relative amounts are similar if differences in the oxidation and reduction level 

 of the substrates are taken into consideration is a very interesting observation, and at 

 present there is no adequate explanation of the results. If erythritol underwent a simple 

 cleavage, it would be expected to give rise to C3 + C^ compound, or to Cg compounds. 

 Since only small amounts of C^ and Cg compounds were formed, it is obvious that either 

 the initial reaction was not a simple cleavage or extensive secondary conversion of the 

 cleavage products must have occurred. The fact that all substrates gave similar products 

 raises the question of whether or not these substrates are converted to 6 or 3 carbon 

 compounds. For erythritol the following two examples may serve as illustrations : 

 References p. 221I222. 



