GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

14. TYPES OF FERMENTATION

14.4. PROPIONIC ACID FERMENTATION AND PROPIONIC ACID BACTERIA

14.4.2. Formation of propionic acid

The reduction of lactate or Pyruvate to propionic acid proceeds via the methylmalonyl-CoA pathway (Fig. 14.4).

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Fig. 14.4. Propionic Acid Fermentation

Initially, pyruvate is converted into oxaloacetate, which is reduced via malate and fumarate to succinate. Electron transport in this segment is coupled with phosphorylation (fumarate Respiration). Subsequently, succinate is transformed into succinyl-CoA and methylmalonyl-CoA, the decarboxylation of which yields propionyl-CoA.

This is the pathway by which propionate is formed in most propionic acid Bacteria, as well as in Veillonella alcalescens and Selenomonas ruminantium.

Propionyl-CoA can also be formed via the acrylyl-CoA pathway (see Fig. 14.4). The intermediate in this process is an acrylic acid derivative, acrylyl-CoA. This is how propionate formation occurs in Clostridium propionicum, Bacteroides ruminicola, and Megasphaera elsdenii.



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