Chapter+9+Microbial+Nutrition+and+Growth

Microbial Nutrition and Growth

Introduction to Microbial Nutrition

• Nutrition: Process by which organisms obtain and utilize nutrients from their environment for cellular activities.

• Nutrients: Substances required for growth, metabolism, and cellular repair.

• Diversity in Requirements: Specific nutrients vary across microorganisms based on habitat and physiology.

Types of Nutrients

• Essential Nutrients: Must be provided to an organism (C, H, O, N, P, S).

• Macronutrients: Required in large quantities for cell structure and metabolism.

• Micronutrients (Trace Elements): Needed in small amounts, important for enzyme function and protein structure maintenance.

Inorganic vs. Organic Nutrients

• Inorganic Nutrients: Lack carbon-hydrogen bonds (examples: minerals, water).

• Organic Nutrients: Contain carbon and hydrogen; derived from living organisms (examples: proteins, lipids).

Chemical Composition of a Bacterial Cell

• Water: Comprises 70% of cell content—most abundant component.

• Proteins: Most prevalent organic compound in bacterial cells.

• Elemental Composition: C, H, O, N, P, S make up 96% of dry weight.

Nitrogen Sources

• Importance: Vital for DNA, RNA, and ATP.

• Availability: Mostly as nitrogen gas (N2) in the atmosphere; few organisms can utilize it directly.

• Conversion: Must be converted to NH₃ for cell utilization; nitrogen-fixing bacteria convert atmospheric nitrogen to ammonia.

Oxygen and Hydrogen Sources

• Oxygen: Critical for cellular functions; major component of organic compounds.

  • Sources: O₂ (atmosphere), bound in compounds like water.

  • Role in aerobic respiration (final electron acceptor).

• Hydrogen: Involved in pH maintenance and cellular energy production.

  • Sources include water and organic compounds.

Phosphorus and Sulfur Sources

• Phosphorus: Essential for nucleic acids and ATP; sourced from phosphate ions (PO₄³⁻) in rocks and ocean minerals.

• Sulfur: Critical for amino acids and vitamins; sourced from rocks and sulfate (SO₄²⁻).

Carbon Sources

• Heterotrophs: Require organic carbon, depend on other organisms.

• Autotrophs: Use inorganic CO₂ and convert it into organic compounds.

Energy Sources

• Phototrophs: Acquire energy from sunlight.

• Chemotrophs: Obtain energy from oxidation of organic or inorganic chemicals.

Nutritional Categories of Microbes

• Autotrophs:

  • Photoautotrophs: Use sunlight for energy and CO₂ for carbon.

  • Chemoautotrophs: Use inorganic substances for energy and CO₂ for carbon.

• Heterotrophs:

  • Photoheterotrophs: Use sunlight for energy but require organic carbon.

  • Chemoheterotrophs: Derive both energy and carbon from organic compounds.

Saprobic and Parasitic Microorganisms

• Saprobic Microorganisms: Decomposers that obtain nutrients from dead organic matter by secreting enzymes to digest complex materials.

• Parasitic Microorganisms: Live on/in a host causing harm.

Diffusion and Osmosis

• Diffusion: Molecules move from high to low concentration; important for gas exchange and nutrient uptake.

• Osmosis: Diffusion of water across a selectively permeable membrane; maintains cell turgor and volume.

Passive Transport Processes in Cells

• Simple Diffusion: Movement of molecules down a concentration gradient.

• Facilitated Diffusion: Movement via specific transport proteins; requires no energy.

Active Transport

• Definition: Movement of nutrients against diffusion gradient or faster than diffusion.

• Energy Requirement: Requires ATP; uses specific membrane proteins and pumps.

• Carrier-Mediated Transport: Molecules actively pumped in/out by receptors.

• Group Translocation: Molecules transported across a membrane and converted simultaneously.

• Endocytosis: Bulk transport of substances by membrane engulfment.

Types of Osmotic Conditions

• Isotonic: Equal solute concentration; no net water movement.

• Hypotonic: Lower solute concentration outside; water enters cell causing swelling.

• Hypertonic: Higher solute concentration outside; water moves out leading to cell shrinkage.

Temperature Adaptations

• Psychrophiles: Thrive in cold environments (<15°C).

• Mesophiles: Optimal growth at moderate temperatures (20-40°C).

• Thermophiles: Prefer hot environments (>45°C).

• Denaturation: High temperatures cause proteins to lose structure and function.

High Temperatures Effects on Organisms

• Protein Denaturation: High temps denature proteins, leading to loss of function.

• Membrane Integrity: Fluidity at high temps can cause membrane lysis.

Low Temperatures Effects on Organisms

• Enzyme Activity Reduction: Low temperatures slow enzyme reactions.

• Membrane Rigidity: Low temps make membranes more rigid impairing function.

Oxygen Requirements

• Aerobes: Need oxygen for growth; possess detoxifying enzymes.

  • Obligate Aerobes: Absolutely require oxygen.

  • Facultative Anaerobes: Can grow with or without oxygen.

  • Microaerophiles: Require lower levels of oxygen.

  • Anaerobes: Cannot tolerate oxygen; found in oxygen-free environments.

Symbiotic Relationships

• Mutualism: Both benefit (e.g., gut bacteria).

• Commensalism: One benefits; the other is unaffected (e.g., barnacles on whales).

• Parasitism: One benefits at the expense of the other (e.g., tapeworms).

Nonsymbiotic Associations

• Antagonism: Competition leading to inhibition or destruction of one.

• Synergism: Cooperative interaction benefiting both.

Biofilms: The Epitome of Synergy

• Definition: Complex communities of microorganisms adhering to surfaces.

• Formation Process: Attachment, colonization, growth, and dispersal.

Quorum Sensing

• Definition: Communication method among bacteria allowing coordinated behavior based on population density.

• Importance: Enables regulation of gene expression in biofilm bacteria.

Importance of Biofilms

• Provide protection against threats like antibiotics.

• Implicated in chronic infections and biofouling in various environments.

Microbial Growth Curve

1. Lag Phase: Adaptation before cell division.

2. Log Phase: Rapid cell division; high susceptibility to antibiotics.

3. Stationary Phase: Growth slows due to nutrient depletion.

4. Death Phase: Decline in viable cells due to resource exhaustion.

Methods of Analyzing Population Growth

• Viable Plate Count: Counting colonies from a diluted sample.

• Turbidometry: Measures broth cloudiness as an indirect growth indicator.

• Direct Microscopic Count: For total cell count.

• Coulter Counter: Electronic counting by detecting resistance changes.

• Flow Cytometry: Counts cells and distinguishes live from dead.

• PCR: Amplifies DNA to detect specific microorganisms.

Summary of Key Concepts

• Nutrient Types: Macronutrients and micronutrients requirements.

• Microbial Growth Phases: Lag, log, stationary, death.

• Oxygen Requirements: Aerobes and anaerobes.

• Temperature Preferences: Psychrophiles, mesophiles, thermophiles.

• pH Preferences: Neutrophiles, acidophiles, alkalinophiles.

• Symbiotic Relationships: Types and their corresponding interactions.