Lecture: Chapter 6 - Microbial Growth (Part Two)

Introduction

• Focus on requirements for microbial growth
• Microbial growth involves cell growth and cell division
• Cells need to metabolize nutrients to grow: involves catabolic reactions for energy and anabolic reactions for macromolecule production
• Functional enzymes are crucial for cell growth

Requirements for Microbial Growth

• Physical Requirements: Temperature, pH, and osmotic pressure
  • Enzymes have optimal temperature and pH
  • Bacteria need isotonic or hypotonic environments; hypertonic environments cause plasmalysis
• Chemical Requirements: Nutrients needed by bacteria
  • Macronutrients: Carbon, Nitrogen, Phosphorus, Sulfur
  • Micronutrients: Growth factors (organic) and trace elements (inorganic)
  • Oxygen: Complex relationship due to its toxicity

Oxygen and Microbial Growth

• Early Earth had no free oxygen
• First cells likely autotrophs, performing photosynthesis
• Oxygen accumulation led to toxic levels and mass extinctions
• Modern cells use enzymes like catalase to detoxify oxides

Oxygen Requirements for Microbes

• Obligate Aerobes: Require oxygen for aerobic respiration
• Facultative Anaerobes: Grow better in oxygen but can also ferment
• Obligate Anaerobes: Cannot survive in oxygen; use anaerobic respiration
• Aerotolerant Anaerobes: Use anaerobic respiration but tolerate oxygen
• Microaerophiles: Require low oxygen levels

Nutritional Classifications

• Energy Sources: Chemicals (chemotrophs) or light (phototrophs)
• Carbon Sources
  • Chemoheterotrophs: Organic molecules
  • Chemoautotrophs: Inorganic carbon (e.g., CO2)
  • Photoheterotrophs: Organic molecules
  • Photoautotrophs: CO2, plants, algae, photosynthetic bacteria

Culturing Bacteria

• Media Types
  • Chemically defined media: Known exact composition
  • Complex media: Made from extracts, unknown composition
  • Reducing media: For obligate anaerobes, impairs oxygen diffusion
  • Selective media: Suppresses unwanted microbes
  • Differential media: Changes color based on microbial growth
  • Enrichment media: Extra nutrients for fastidious bacteria

Bacterial Growth Process

• Binary Fission: Cell duplicates its chromosome, elongates, and divides
• Growth Curve Phases
  • Lag phase: Adjustment period
  • Log phase: Rapid growth
  • Stationary phase: Nutrients deplete, waste accumulates
  • Decline phase: More deaths than replications

Conclusion

• Understanding microbial growth requirements and processes is essential for effectively culturing and studying bacteria in lab environments. This includes knowing environmental conditions, nutrient needs, and the effects of oxygen and other factors on microbial life.