254 BACTERIOLOGICAL CHEMISTRY 



All alternative route is that glycerophosphate is oxidised 

 to phosphoglyceric acid which gives pyruvic acid which 

 is reduced to propionic acid. 



When glucose is dissimilated by propionic acid 

 bacteria, phosphoglyceric acid is produced and can be 

 isolated if toluene and sodium fluoride are present (the 

 latter inhibiting further breakdown of the phospho- 

 glyceric acid). Pjrruvic acid can be fixed by using 

 sodium sulphite, but acetaldehyde cannot be detected. 

 This suggests that the propionic acid bacteria have no 

 carboxylase and do not split pyruvic acid to give acetalde- 

 hyde and carbon dioxide, as do the yeasts. Some strains 

 also produce lactic acid, but others do not. Lactic acid, 

 however, is fermented by all strains with formation of 

 propionic acid. Succinic and acetic acids are also formed, 

 but undergo further breakdown, the ratio of propionic 

 acid to acetic acid increasing during the fermentation. 

 If the culture is buffered by sodium bicarbonate the 

 ratio of propionic acid to acetic acid remains approxi- 

 mately constant. Wood, Stone and Werkman suggested 

 that propionic acid was formed by the following scheme : — 



2H.F0, 



CeHi.Og — > Hexosephosphate ^ CHoO.PO.Ha.CHOH.CHO 



(glucose) _2H20 (Triosc phosphate) 



— HsPO^CHaO.POaHo.CHOH.COOH < Noit-reducing 



(phosphoglyceric acid) substance 



CH3CO.COOH 



~2H 



+ 2H 



CH3CHOH.COOH 



(lactic acid) 



,or 



CH3CO.CHO + H3PO, 



(methylglyoxal) 



+ 2H 

 — H3O 



CH3CH2COOH 



(propionic acid) 



