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Chapter 2: Biological Reactions in Microbial Cells

1. Introduction to Microbial Reactions

• Microorganisms play a vital role in breaking down large biological molecules, essential for waste decomposition in the environment.

• Diagnostic microbiology depends on the growth of pathogens on specialized media to identify species that may appear morphologically identical.

2. Media for Culturing Microorganisms

2.1 Selective Media

• Contains chemical compounds to inhibit certain microorganisms while allowing others to grow (e.g., high salt concentration).

2.2 Differential Media

• Contains indicators (like dyes) that allow differentiation between species based on chemical reactions during growth.

• Example: Growth on mannitol salt agar distinguishes between Staphylococcus aureus (which ferments mannitol and produces acid turning the medium yellow) and Staphylococcus epidermidis (which does not change the medium's color).

3. Metabolic Pathways and Enzymes

• Microorganisms can adapt their metabolic pathways based on available nutrients, synthesizing only the necessary enzymes for immediate needs.

• Example: Sulfur bacteria thrive in hot springs by utilizing sulfur compounds as electron acceptors.

• Enzyme measurement can inform about a cell's overall functioning, as seen in human liver function tests (e.g., hepatitis, cirrhosis).

4. Industrial Applications of Microbial Metabolism

4.1 Uses in Food Production

• Microorganisms like yeast and lactic acid bacteria are crucial in food industry.

  • Fermented Products:

    • Wine: Fermented grape juice using yeasts (e.g., Saccharomyces ellipsoideus).

    • Beer: Made from malted barley, using specific yeast strains (e.g., Saccharomyces cerevisiae).

    • Bread: Yeast fermentation causes dough to rise through carbon dioxide production.

    • Cheese & Yogurt: Lactic acid bacteria convert milk sugars into lactic acid, souring the milk.

4.2 Cultivating Specific Microbes for Benefits

• Examples include using Rhizobium for nitrogen fixation in leguminous plants, and mushrooms cultivated for food.

5. Enzyme Reactions and Diagnostic Microbiology

• A battery of biochemical tests in microbiology helps identify specific microorganisms based on their enzymatic reactions.

• Tests can measure gas production or enzymatic breakdown reactions, aiding in rapid diagnosis of infections (e.g., urine tests).

6. Types of Metabolites

6.1 Primary Metabolites

• Produced via major fermentation pathways and can be harvested in significant yields. Examples: citric acid, ethanol, lactic acid.

6.2 Secondary Metabolites

• Non-essential compounds produced when nutrients are scarce, such as antibiotics.

  • Antibiotics significantly impact medicine; they are mostly produced by fungi or specific bacteria.

7. Microorganisms in Scientific Research

• Similarities in metabolic processes in microorganisms and higher organisms unique for genetic research (e.g., genetic mapping).

• Techniques developed from microbial studies apply to advanced genetic engineering methods to synthesize valuable compounds like insulin, growth hormones, and vaccines.

8. Environmental Applications

• Microorganisms contribute to nutrient recycling and organic matter decomposition, making them essential in ecosystem functioning.

9. Summary of Key Concepts

• Metabolism: Overall reactions of catabolism, anabolism, and repair in living cells.

• Biological Molecules: Comprised mainly of carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, and trace elements.

• Carbohydrates: Organic compounds consisting of sugars.

• Lipids: Fats containing glycerol and fatty acids.

• Proteins: Composed of 20 different amino acids; essential for various biological functions.

• Hydrocarbon Metabolism: Few microorganisms can utilize hydrocarbons (e.g., certain Pseudomonas strains). Used in bioremediation, such as oil spill clearance.

10. Antibiotics Overview

References

• Lee, G. & Bishop, P. (2015). Microbiology and Infection Control for Health Professionals. Pearson Education Australia.