mICROBIO

Microbial Nutrition, Cultivation, and Growth

Microbial Nutrition

• Microorganisms require nutrients for cellular component synthesis and energy production.

• Nutritional requirements vary among species.

Growth Requirements for Microorganisms

• Microbial growth results in population formation; cell size increases through metabolism.

• Requirements classified as:

  • Physical Requirements:

    • Temperature:

      • Psychrophiles: Grow at 0°C, optimum 15°C.

      • Psychrotrophs: Grow at 20-30°C, responsible for low-temp food spoilage.

      • Mesophiles: Optimum 25-40°C, pathogenic bacteria grow best at 37°C.

      • Thermophiles: Thrive at 50-60°C, used in organic composting.

      • Hyperthermophiles: Can grow at 80°C or higher.

    • pH: Optimal near neutrality (pH 6.5-7.5); acidophiles thrive in acidic conditions.

    • Osmotic Pressure: Microbes require appropriate osmotic pressure to retain water and nutrients; high osmotic pressure can cause plasmolysis.

Chemical Requirements

1. Water: Makes up 80-90% of microbial cellular structure.

2. Carbon:

   • Autotrophs use CO2 as carbon source.

   • Heterotrophs use organic compounds.

3. Oxygen:

   • Aerobic bacteria require oxygen; anaerobes avoid it.

4. Nitrogen: Needed for amino acids and nucleic acids; nitrogen-fixing bacteria included.

5. Sulfur: Important for protein synthesis.

6. Phosphorus: Essential for nucleic acids and phospholipids.

7. Trace Elements: Needed for enzyme synthesis (e.g., iron, zinc).

8. Growth Factors: Some microorganisms need organic growth factors (e.g., vitamins).

Microbial Cultivation/Culture Media

• Medium: Growth environments for selected microorganisms, can be defined chemically or organic.

• Culture Types: Pure (single organism) vs. Mixed (multiple organisms).

• Sterility: Required before inoculation.

• Nutrient Sources: Commonly, nutrient broth/agar, or specialized media for fungi and anaerobes.

• Culture Media Types:

  • Simple Media: Non-fastidious bacteria.

  • Enrichment Media: Supports fastidious microbes.

  • Selective Media: Encourages certain microorganisms while inhibiting others.

  • Differential Media: Distinguishes between different bacterial species based on characteristics.

Microbial Growth Patterns

• Reproduction: Takes place through various processes, including binary fission in bacteria.

• Growth Curve Phases:

  1. Lag Phase: Adaptation to new environment.

  2. Log Phase: Rapid, optimal growth; generation time varies.

  3. Stationary Phase: Growth equals death rate; plateau.

  4. Decline Phase: Rapid cell death occurs.

Isolation Methods

• Streak Plate Method: Used for isolating pure cultures.

• Pour Plate Method: Dilution is used for isolation in solidified medium.