Lecture 7_ Bacterial Nutrient (1)

Learning Objectives

  • Bacterial Nutrition

    • Major nutrients: carbon, oxygen, sulfur, nitrogen

    • Minor nutrients: zinc, manganese, copper

    • Oxygen requirements: some bacteria require oxygen, while others do not

    • Uptake mechanisms for nutrients

  • Culture Strategies & Techniques

    • Enrichment: Growing bacteria by providing specialized nutrients

    • Isolation: Separating specific bacteria from a mixed culture

    • Preservation: Techniques for keeping bacteria alive for future use

Microbial Growth Requirements

  • Autotrophy (Self Feeding)

    • Does not require organic carbon for energy or structure

    • Obtains carbon from inorganic sources (e.g., CO2)

      • Phototrophy: Using light for energy

      • Lithotrophy: Using inorganic materials (e.g., manganese, iron)

  • Heterotrophy

    • Requires organic carbon from other organisms

    • Can be:

      • Parasites/Pathogens: Harmful to hosts

      • Decomposers: Break down dead organic matter

  • Importance:

    • Autotrophs generate oxygen and organic food in ecosystems

    • Heterotrophs are crucial for organic matter recycling

Major Nutrients

  • Nutrients essential for bacterial cell mass, growth, and survival:

    • Carbon (C): ~50% of cell mass, from CO2 and organic sources

    • Nitrogen (N): ~15% of dry weight; some bacteria fix N2 or use ammonia

    • Sulfur (S) and Phosphorus (P): ~4% of dry weight; essential for proteins (S) and nucleic acids/ATP (P)

Micronutrients

  • Micronutrients: Needed in small amounts for enzyme functioning:

    • Organic Trace Elements: Important for cofactors (e.g., FAD, NAD, CoA)

    • Inorganic Trace Elements: Required for enzymatic functions (e.g., magnesium, molybdenum, iron)

    • Iron is essential for the electron transport chain; selenium is incorporated into proteins

Oxygen Requirements

  • Forms of oxygen include:

    • Natural: H2O, CO2, O2

    • Reactive forms: can cause damage to cells

  • Varied oxygen needs:

    • Aerobic bacteria: Require oxygen to survive

    • Anaerobic bacteria: Oxygen is toxic; some use enzymes to detoxify reactive forms

      • Important enzymes: Superoxide dismutase (SOD), Catalase

Bacterial Response to Oxygen

  • Different metabolic responses to oxygen:

    • Obligate aerobes: Need oxygen; e.g., Mycobacterium tuberculosis

    • Facultative aerobes: Can survive with or without oxygen; e.g., E. coli

    • Microaerophiles: Require low oxygen levels, too much is toxic; e.g., Helicobacter pylori

    • Aerotolerant anaerobes: Do not use oxygen but can survive in its presence; e.g., Lactobacillus

    • Obligate anaerobes: Oxygen is lethal; e.g., Clostridium botulinum

Nutrient Uptake

  • Bacteria uptake nutrients through various transport mechanisms:

    • Passive transport: Moves along gradient without energy (e.g., diffusion)

    • Active transport: Moves against gradient; requires energy (ATP)

      • Symport: Both molecules move in the same direction

      • Antiport: One moves in and the other out

  • ABC Transporters: Utilize ATP to change the shape of proteins for nutrient transport

Phosphotransferase (PTS) System

  • Special transport system for sugars (e.g., glucose):

    • Transports glucose while modifying it to glucose-6-phosphate

    • Prevents accumulation inside the cell, facilitating continuous uptake

    • Important for antibiotic research due to sugar uptake targeting

Limiting Nutrients

  • Key nutrients that can limit growth include:

    • In the environment: Phosphate, nitrogen, and sulfur

    • In hosts: Iron, magnesium, and selenium

Special Mechanisms for Scarce Nutrients:

  1. Phosphatase: Releases phosphate from phosphoric acid esters

  2. Siderophores: Iron-binding molecules that help bacteria obtain iron from hosts

Importance in Disease:

  • Some bacteria use siderophores to overcome nutrient scarcity in hosts (e.g., Bordetella pertussis)

  • Scientists explore drugs targeting siderophores to combat infections

Laboratory Cultures

  • Culture media: Nutrient solutions that support growth

    • Defined media: Exact composition known

    • Undefined media: Natural extracts, variable composition

Growth Methods:

  • Aerobic Growth: Easier for bacteria needing oxygen; uses incubators to maintain conditions

  • Anaerobic Growth: Requires complete oxygen removal for strict anaerobes

    • Methods include anaerobic jars or reducing agents in media

Special Growth Environments

  • Some bacteria require unique conditions:

    • Mycobacterium leprae: Grown in armadillos

    • Chlamydiae/Rickettsiae: Obligate intracellular; require mammalian cell cultures

Uses of Growth Media

  • General growth media fosters populations for research and industry

  • Selective media: Encourages growth of certain bacteria while inhibiting others

  • Differential media: Distinguishes bacteria based on traits (e.g., lactose fermentation)

Enrichment Culture and Isolation

  • Enrichment culture: Grows specific bacteria by altering conditions

  • Isolation: Pure cultures obtained through methods like streak plating

  • Techniques for culture preservation are essential for maintaining valuable bacterial strains:

    1. Refrigeration

    2. Freeze-drying (lyophilization)

    3. Freezing at -80°C with glycerol to prevent damage

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