Microbial Growth and Physiology Lecture 5

Lecture 5: Growth and Physiology

• Lecture 5 covers microbial growth and physiology, focusing on bacterial growth.
• The lecture discusses prokaryotic cell morphology, bacterial structure, gram staining, bacterial shapes, and bacterial cell structure (G+ve, G-ve, Archaea), including cell walls, outer membranes, and appendages.
• Learning outcomes include microbial growth and physiology, bacterial growth by binary fission, bacterial growth on solid and liquid media, growth phases in liquid bacterial culture, measurements of bacterial growth (direct and indirect), and growth requirements.

Growth of Bacteria

• Bacteria divide by binary fission.
• The chromosome divides into two identical copies.
• The copies segregate to opposite ends of the cell.
• A cell wall forms down the middle of the cell, producing two identical new cells.
• Bacterial growth is exponential (1->2->4->8...).
• Generation times (time for a bacterial mass to double) can be as fast as 20 minutes.
• Rapid growth can contribute to adaptability in hostile environments, leading to selective pressures where mutant cells that survive will rapidly grow and take over,

Growth Media

• Agar melts at 100°C and solidifies at 40°C.
• Agar is sterilized by autoclaving.
• Bacteria grow as colonies on solid media (agar plates).
• Single colony purification is possible.
• Liquid broths and Nutrient agar plates are used for culturing and observing growth in a lab setting.
• A cotton wool bung and gas exchange is used for keeping contents sterile when incubating standing or agitated samples in liquid media.

Growth Phases

• Lag phase: Adaptation period, where cells adjust to new environment.
• Logarithmic (exponential) phase: Cells multiply rapidly at their maximum rate.
• Stationary phase: Lack of nutrients and build-up of toxic metabolic intermediates balance cell multiplication with cell death.
• Death phase: Number of viable cells decreases.

Measurements of Bacterial Growth

• Direct measurements:
  • Total cell count: Using a microscope and counting chamber.
  • Total viable count: Diluting cells in culture and spreading them on nutrient agar plates; only viable cells reproduce into colonies.
  • Counting chamber used for determining cell number in a volume of sample.
• Indirect measurements:
  • Turbidity (cloudiness): Measures live and dead cells using a spectrophotometer to measure the amount of light that passes through a liquid culture.

Bacterial Growth Requirements

• **Nutrients:**Water, carbon (carbohydrate), nitrogen (protein), inorganic salts, iron (siderophores), oxidation of organic compounds (carbohydrates, lipids, proteins).
• Environmental conditions: Temperature (20°C-110°C), pH (4.0-9.0), atmosphere (oxygen/no oxygen),
• Energy: Derived from the enzymatic breakdown of organic substrates (carbohydrates, lipids, proteins) in a process called catabolism. Energy generated from catabolism is used for synthesis of cellular constituents in a process called anabolism.

Extremophiles and Other Environments

• Extremophiles grow in extreme environments (high/low temperatures, pH, pressure, salt).
• Examples include hyperthermophiles (extreme heat), psychrophiles (extreme cold), acidophiles (extreme acidity), alkaliphiles (extreme alkalinity), barophiles (high pressure), halophiles (high salt).
• Enzymes from extremophiles are valuable in protein science and protein engineering.
• Bacteria can obtain energy from diverse sources (plastic, rubber, toxic compounds).

Further Reading

• Recommended textbooks: "Brock, Biology of Microorganisms," by Madigan, Martinko, and Parker (10th ed.).
• Specific chapters to read:
  • Chapter 5 "Nutrition, Laboratory Culture and Metabolism of Microorganisms."
  • Chapter 6 "Microbial Growth."

This quiz covers key concepts from Lecture 5 on microbial growth and physiology. Topics include bacterial cell structure, gram staining, and the process of bacterial growth through binary fission. Test your understanding of prokaryotic morphology, growth phases, and measurement methods in bacterial culture.