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