Physiology and Screening of Microorganisms Chapter 1

Course Information

• Course Title: Physiology and Screening of Industrial Microorganisms
• Course Code: SCCG 3673
• Academic Year: 2024/2025
• Level: 1
• Instructor: Dr. Praseetha Prabhakaran
• Email: [email protected]
• Location: T02, Level 4

Chapters

• Chapter 1: Introduction
• Chapter 2: Microbial Growth Requirement
• Chapter 3: Methods of Isolating Pure Cultures
• Chapter 4: Screening of Anaerobic Microorganisms
• Chapter 5: Screening of Thermophilic Microorganisms
• Chapter 6: Screening of Alkalophilic Microorganisms
• Chapter 7: Screening of Acidophilic Microorganisms

Microbial Growth Based on Oxygen Requirement

• Organism's oxygen requirement
  • Test tubes labelled a to f illustrate growth location based on oxygen requirement in Fluid Thioglycolate Medium (FTM).
  • Images display different growth patterns in the tubes showing how microbes respond to different oxygen conditions.

Anaerobes

• Obligate aerobes
  • Require oxygen at atmospheric levels (21% O₂).
  • Grow as a film (scum) or layer on the top of the liquid medium.
• Obligate anaerobes
  • Killed by exposure to even small amounts of oxygen.
• Facultative anaerobes
  • Grow in both aerobic and anaerobic conditions.
  • Prefer aerobic conditions.
• Aerotolerant anaerobes
  • Only grow in anaerobic conditions.
  • Presence of oxygen has no effect on their growth.
• Microaerophiles
  • Need a low level of oxygen (2-10% O₂).
  • High oxygen concentrations are toxic.

Anaerobe Classification

• Group | Relationship to O₂ | Type of Metabolism | Example | Habitat
• --- | --- | --- | --- | ---
• Obligate | Required | Aerobic respiration | Micrococcus luteus | Skin, dust |
• Microaerophilic | Required but at levels lower than atmospheric | Aerobic respiration | Spirillum volutans | Water |
• Aerotolerant | Not required & presence of O₂ has no effect | Fermentation | Streptococcus pyogenes | Upper respiratory tract |
• Facultative | Not required, but growth is better with O₂ | Aerobic, anaerobic respiration, fermentation | Escherichia coli | Mammalian intestine |
• Obligate | Harmful or lethal | Fermentation or anaerobic respiration | Methanobacterium formicicum | Sewage sludge, digesters, anoxic lake sediments |

Why Oxygen is Lethal to Obligate Anaerobes

• Oxygen is a powerful oxidant and a good electron acceptor for respiration.
• Reduction of oxygen (O₂ to H₂O) in respiration produces harmful oxygen by-products.

Oxygen By-Products and Cellular Defense Mechanisms

• Superoxide dismutase (SOD)
  • Enzyme catalyzing the dismutation of superoxide radicals into oxygen or hydrogen peroxide.
  • Important antioxidant defense mechanism to protect cells from oxygen damage.
• Catalase
  • Enzyme that decomposes hydrogen peroxide into water and oxygen.
  • Protects cells from oxidative damage by Reactive Oxygen Species (ROS).
• Peroxidase
  • Enzyme that converts hydrogen peroxide to water in the presence of hydrogen ions (NADH).
  • Found in oxygen-tolerant anaerobic bacteria.

Types of Respiration

• Aerobic respiration
  • Glucose + Oxygen → Water + Carbon Dioxide + Energy (2870 kJ)
• Anaerobic respiration (alcohol fermentation)
  • Sugar → Ethanol + Carbon Dioxide + Energy (210 kJ)
• Anaerobic respiration (lactic acid fermentation)
  • Sugar → Lactic Acid + Energy (150 kJ)

Other Fermentative Pathways

• Propionibacterium: propionic acid fermentation
• Clostridium: butyric acid fermentation
• Enterobacter: butanediol fermentation

Fermentation Products

• List of organisms and their fermentation products.
• Fermentation products include:
  • Propionic acid
  • Lactic acid
  • Ethanol
  • Acetic acid
  • CO₂ (and more listed in table)

Classification of Important Anaerobes

• Gram-positive Cocci:
  • Anaerobic Streptococcus
  • Anaerobic Staphylococcus -Peptostreptococcus
• (species examples provided)*
• Gram-positive Bacilli: -Sporeforming (species examples provided)
  • Non-sporeforming (species examples provided)
• Gram-negative Cocci: -Veillonella
• (species examples provided)*
• Gram-negative Bacilli: -Bacteroides -Prevotella -Porphyromonas
• Fusobacterium
• (species examples provided)*

Examples of Important Anaerobes

• Escherichia coli:
  • Facultative anaerobe
  • Often harmless; some strains are harmful.
• Streptococcus pyogenes:
  • Aerotolerant anaerobe.
  • Associated with mild to life-threatening infections.
• Staphylococcus genus:
  • Facultative anaerobe.
  • Some strains cause infections; others are harmless.
• Clostridium genus:
  • Obligate anaerobe.
  • Spore-forming; some strains produce toxins causing serious diseases (e.g., botulism, tetanus).