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.