9.2 .pdf

Oxygen-Free Environments: Some ecosystems lack oxygen, like deep oceans, soil, marshes, and inside animal bodies. Thioglycolate Tube Cultures: Used to test bacterial oxygen needs. Starts with a medium that has low oxygen due to autoclaving. Oxygen gradually enters from the top dur...

Oxygen-Free Environments: Some ecosystems lack oxygen, like deep oceans, soil, marshes, and inside animal bodies. Thioglycolate Tube Cultures: Used to test bacterial oxygen needs. Starts with a medium that has low oxygen due to autoclaving. Oxygen gradually enters from the top during incubation. Bacterial growth varies based on oxygen availability. Bacterial Types and Growth: Obligate Aerobes (Tube A): Grow only at the top where oxygen is abundant (e.g., Mycobacterium tuberculosis). Obligate Anaerobes (Tube B): Grow only at the bottom, where oxygen is absent (e.g., Bacteroidetes in the gut). Facultative Anaerobes (Tube C): Can grow with or without oxygen (e.g., Staphylococci). Aerotolerant Anaerobes (Tube D): Indifferent to oxygen; do not use it but aren't harmed by it (e.g., lactobacilli). Microaerophiles (Tube E): Require low oxygen levels (1%-10%) for growth (e.g., Campylobacter jejuni). Health Implications: Obligate anaerobes can cause infections (e.g., Clostridium difficile, C. tetani, C. perfringens). Antibiotic use can disrupt gut balance, allowing harmful anaerobes to thrive. Special Equipment: Anaerobic jars and chambers are used to grow obligate anaerobes without oxygen. Key Terms: Optimum Oxygen Concentration: Ideal oxygen level for growth. Minimum Permissive Oxygen Concentration: Lowest oxygen level that allows growth. Maximum Permissive Oxygen Concentration: Highest oxygen level tolerated without harm. Reactive Oxygen Species (ROS): Byproducts of aerobic respiration that need to be detoxified. Formed even in organisms that don't use aerobic respiration. Key Enzymes for Detoxification:  1. Superoxide Dismutase (SOD): ○ Breaks down superoxide anions (O2−) into hydrogen peroxide (H2O2) and oxygen (O2). 2. Peroxidase: ○ Converts hydrogen peroxide into water (H2O) and oxidized compounds. 3. Catalase: ○ Converts hydrogen peroxide into water and oxygen. Reactions: 1. Peroxidase Reaction: ○ X− + 2H+ + H2O2 → oxidized-X + 2H2O 2. SOD Reaction: ○ 2O2− + 2H+ → H2O2 + O2 3. Catalase Reaction: ○ 2H2O2 → 2H2O + O2 Types of Organisms: Obligate Anaerobes: Lack all three enzymes. Aerotolerant Anaerobes: Have SOD but no catalase. Testing for Catalase: Used to distinguish between streptococci (catalase-negative) and staphylococci (catalase-positive) by adding hydrogen peroxide, which produces bubbles if catalase is present. Capnophiles: Bacteria that thrive in high CO2 and low oxygen. Can be grown in a candle jar, which burns oxygen and releases CO2.