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
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
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: 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
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
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
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
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
Key nutrients that can limit growth include:
In the environment: Phosphate, nitrogen, and sulfur
In hosts: Iron, magnesium, and selenium
Phosphatase: Releases phosphate from phosphoric acid esters
Siderophores: Iron-binding molecules that help bacteria obtain iron from hosts
Some bacteria use siderophores to overcome nutrient scarcity in hosts (e.g., Bordetella pertussis)
Scientists explore drugs targeting siderophores to combat infections
Culture media: Nutrient solutions that support growth
Defined media: Exact composition known
Undefined media: Natural extracts, variable composition
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
Some bacteria require unique conditions:
Mycobacterium leprae: Grown in armadillos
Chlamydiae/Rickettsiae: Obligate intracellular; require mammalian cell cultures
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: 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:
Refrigeration
Freeze-drying (lyophilization)
Freezing at -80°C with glycerol to prevent damage