Factors Affecting Microbial Growth

Key Considerations

• Temperature
• pH
• Water Availability
• Oxygen

These factors impact microbial growth and will be discussed in detail.

Temperature and Microbial Growth

• Temperature affects the molecular components of the cell.

Cardinal Temperature

• Minimum Cardinal Temperature:
  • Membrane lacks fluidity and gels.
  • Impacts transport, slowing growth until it stops.
• Maximum Cardinal Temperature:
  • Membrane becomes too fluid, causing thermal lysis.
  • Proteins denature, losing function.
• Optimal Cardinal Temperature:
  • Enzymes operate at optimum for maximum growth.
  • For every 10°C rise in temperature, enzymatic reaction rate doubles.

Temperature Growth Rates

• Organisms thrive in upper temperature regions.
• Graph trends lean to the right, indicating optimal growth.

Microorganism Temperature Classifications

• Organisms are grouped by required temperature ranges for growth.

Psychrophiles

• Definition: "Psycho" means cold, "phile" means liking.
• Characteristics:
  • Prefer cold temperatures.
  • Found in cold environments (e.g., Antarctica).
  • Example: Polomonas vaculata

Mesophiles

• Definition: "Meso" means middle.
• Characteristics:
  • Prefer mid-range temperatures.
  • Found in warm-blooded animals, terrestrial, aquatic environments.
  • Example: E. coli
  • Optimal temperature: 39°C

Thermophiles

• Definition: "Thermo" means heat.
• Characteristics:
  • Prefer high temperatures.
  • Found in hot environments (e.g., hot springs, ocean sediments).
  • Example: Geobacillus stereothermophilus

Hyperthermophiles

• Definition: "Hyper" means above or beyond.
• Characteristics:
  • Prefer very high temperatures.
  • Found in extreme environments (e.g., hydrothermal vents).
  • Example: Thermococcus cellar, Pileuberus fumari
  • Optimal temperature: 113°C

Extremophiles

• Definition: Organisms living in extreme conditions.

Important Concepts

• Understanding the classifications and characteristics of microorganisms based on temperature preferences is crucial for studying microbial growth.
• The trend in temperature growth rates is important for identifying optimal growth conditions.