Chapter Six: Microbial Growth - Part One

Overview

• Importance of microbial growth:
  • Research on pathogens for disease treatment
  • Biotech applications such as food production (yeast growth for bread) and genetic engineering (recombinant DNA for vaccines and hormones)
• Focus on bacteria and growth requirements
  • Bacteria are living, metabolizing cells
  • Requirements divided into physical and chemical categories

Physical Requirements for Growth

Temperature

• Optimal Temperature: Where microbes grow fastest
• Temperature Range: Minimum and maximum temperatures for growth
• Types of temperature requirements:
  • Psychrophiles:
    • Cold-loving; optimal at ~10°C
    • Range: -10°C to 20°C
    • Found in polar regions, ocean depths
  • Cyclotropes:
    • Optimal at ~22°C (room temperature)
    • Range: 0°C to 30°C
    • Can spoil food at refrigerator temp (4°C)
  • Mesophiles:
    • Optimal at ~37°C (body temperature)
    • Range: 10°C to 50°C
    • Includes human pathogens
  • Thermophiles:
    • Optimal at ~60°C
    • Range: 40°C to 70°C
    • Found in hot springs
  • Hyperthermophiles:
    • Optimal at 90°C to 100°C
    • Range: 70°C to 110°C
    • Found in hydrothermal vents

pH

• pH Scale: 0 (acidic) to 14 (basic), with neutral around 7
• Types of pH requirements:
  • Neutrophils: Prefer neutral pH (optimal ~7)
  • Acidophiles: Optimal pH ~3, range: 1 to 5.5
  • Alkylophiles: Optimal pH ~9.5, range: 7.5 to 11.5

Osmotic Pressure

• Osmosis: Diffusion of water across a membrane
• Isotonic: Same solute concentration; no osmosis
• Hypotonic: Lower solute concentration; osmotic lysis possible if cell wall is weak
• Hypertonic: Higher solute concentration; causes plasmolysis and cell death

Chemical Requirements for Growth

Macronutrients

• Carbon: Forms basis of all organic molecules
• Nitrogen: Essential for nucleic acids and proteins
• Phosphorus: Important for nucleotides and ATP
• Sulfur: Found in amino acids and important for disulfide bonds in proteins

Micronutrients

• Growth Factors: Organic molecules required in small amounts
• Trace Elements: Inorganic metals serving as cofactors
• Essential for forming active sites on enzymes

Key Takeaways

• Bacterial growth relies on maintaining specific physical and chemical conditions
• Enzyme activity and metabolism are regulated by these conditions
• Laboratory growth of bacteria involves controlling these conditions in media and environment