GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

14. TYPES OF FERMENTATION

14.6. BUTYRIC ACID AND ACETONE-BUTANOL FERMENTATION. CLOSTRIDIA

14.6.2. Glucose fermentation by clostridia

Glucose Catabolism proceeds via The Glycolytic Pathway. Hydrogen generated during the dehydrogenation of glyceraldehyde 3-phosphate is transferred to organic acids or ketones derived from Pyruvate or acetyl-CoA. A typical pathway of glucose Fermentation by clostridia is characteristic of Clostridium butyricum and Clostridium acetobutyricum (Fig. 14.6).

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Fig. 14.6. Glucose fermentation by Clostridium butyricum and Clostridium acetobutyricum

The formation of butyrate begins with the Condensation of two molecules of acetyl-CoA to yield acetoacetyl-CoA, which is subsequently reduced to β-hydroxybutyryl-CoA and butyryl-CoA. Free acetate and a molecule of ATP can be formed from acetyl-CoA via the action of phosphotransacetylase and acetate kinase. As acetate and butyrate accumulate and the medium becomes increasingly acidic, the synthesis of Enzymes that catalyze the formation of acetone and butanol is induced. Acetoacetyl-CoA is converted to acetoacetate, whose decarboxylation yields acetone. The reduction of acetone yields propanol. The reduction of butyryl-CoA yields butanol. Ethanol may also be produced during glucose fermentation by clostridia (via the reduction of acetyl-CoA). Molecular hydrogen can be released from NADH generated during the dehydrogenation of glyceraldehyde 3-phosphate and the Oxidation of Pyruvate. The greater The amount of molecular hydrogen produced, the fewer organic hydrogen acceptors (acetoacetyl-CoA) need to be synthesized.

Because acetone, 2-propanol, and butanol are important organic Solvents, the fermentation processes carried out by clostridia are of great industrial significance.