Fermentation Sp25

Fermentation Overview

  • Definition: Fermentation is the process that allows for the completion of glucose catabolism in an anaerobic environment.

  • Electrons: Electrons are sourced from NADH (or NADPH) and donated to pyruvate.

  • Byproducts: Common byproducts include alcohols, carboxylates, hydrogen, and carbon dioxide.

  • Energy Storage: Most fermentations do not produce ATP beyond what is generated during glycolysis. Microbes respond by heaving high substrate consumption and excreting large amounts of byproducts.

Glycolysis and Energy Production

  • ATP Yield:

    • Produces a net gain of 2 ATP through substrate-level phosphorylation.

  • Steps Involved:

    • 2-Phosphoglycerate, pyruvate[ADP, P] transition to produce phosphoenolpyruvate (PEP) and back to pyruvate. This results in the release of energy during glycolysis.

Pathways of Fermentation

  • Alcoholic Fermentation:

    • Converts pyruvate into ethanol and carbon dioxide.

    • Involves the formation of molecules such as acetaldehyde and ethanol from pyruvate.

  • Heterolactic Fermentation:

    • Produces 1 molecule of lactic acid, 1 molecule of ethanol, and 1 molecule of carbon dioxide.

  • Homolactic Fermentation:

    • Produces two molecules of lactic acid.

  • Mixed-Acid Fermentation:

    • Produces various acids including acetate, formate, lactate, and succinate, alongwith ethanol, hydrogen, and carbon dioxide.

Diagnostic Applications in Microbiology

  • Purpose: Rapid biochemical tests help identify disease-causing microbes and facilitate antibiotic prescriptions.

    • Tests:

      • Phenol Red Broth Test: Tests the fermentation ability of the microbe.

      • Sorbitol MacConkey Agar: Identifies strains like O157:H7, which fail to ferment sorbitol compared to nonpathogenic E. coli species.

Methyl Red and Voges-Proskauer Tests

  • Methyl Red Test:

    • Tests for mixed acid fermentation; turns red below pH 4.4 and yellow above pH 6.2. Positive Result: Red color indicates acid production.

  • Voges-Proskauer Test:

    • Indicates production of acetoin; positive result shows deep red color. Negative results appear copper-colored.

Summary of Key Concepts

  • Energy Sources: ATP, NADH, and FADH2 are critical for cell energy management.

  • Catabolic Pathways:

    • Main types include fermentation, respiration, and photoheterotrophy, emphasizing that prokaryotes can metabolize diverse organic materials, including sugars and lipids.

  • Glucose Catabolism Pathways:

    • Glycolysis: Produces 2 ATP and 2 NADH.

    • Entner-Doudoroff (ED) Pathway: Produces 1 ATP, 1 NADH, and 1 NADPH.

    • Pentose Phosphate Pathway: Yields 1 ATP and 2 NADPH.

  • Fermentation Completion: Finalizes catabolism without utilizing an electron transport chain.