Lecture: Microbial Nutrition and Growth (Microbiology: A Systems Approach, Chapter 9)

Introduction

• Microorganisms, like all organisms, need nutrients to grow, develop, and divide.
• Nutrients are obtained from the environment and are essential for cellular activities.

Essential Elements

• Essential elements for all living organisms: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Sulfur (S).
• Macronutrients: Required in large quantities (C, H, O, N, P, S).
• Micronutrients: Trace elements like Copper (Cu), Zinc (Zn), Iron (Fe) needed in smaller amounts.

Types of Nutrients

• Organic Nutrients: Contain carbon and hydrogen (e.g., vitamins).
• Inorganic Nutrients: Lack carbon (e.g., minerals like iron, zinc).

Sources of Elements

• Carbon: From CO2 (autotrophs) or organic molecules (heterotrophs).
• Nitrogen: From atmospheric N2 or compounds like nitrate (NO3-), nitrite (NO2-), ammonia (NH3).
• Oxygen: From the atmosphere or environment.
• Hydrogen: From organic molecules or water.
• Phosphorus: From inorganic sources like phosphate in minerals.
• Sulfur: Found in environment, essential for some amino acids.

Nutritional Types

• Heterotrophs: Obtain carbon from organic compounds.
• Autotrophs: Obtain carbon from CO2.
• Phototrophs: Obtain energy from sunlight.
• Chemotrophs: Obtain energy from chemical compounds.
• Photoautotrophs: Use sunlight and CO2.
• Chemoheterotrophs: Use organic molecules for both energy and carbon.
• Variations like chemoautotrophs using inorganic substances.

Cell Composition

• Bacterial cell: 70% water, 97% dry weight composed of organic compounds.
• Major organic compounds: Proteins, RNA, DNA, carbohydrates, lipids.

Cellular Processes and Transport

• Diffusion: Movement from high to low concentration.
• Osmosis: Water diffusion across a membrane.
• Tonicity: Isotonic, hypotonic, hypertonic environments affecting cell state.
• Passive Transport: Simple diffusion (no energy required).
• Facilitated Diffusion: Requires transport proteins.
• Active Transport: Requires energy to move substances against gradient.
• Endocytosis: Bulk transport into the cell (phagocytosis - solids, pinocytosis - liquids).

Environmental Factors Influencing Growth

• Temperature: Varying optimal temperatures for different types.
  • Psychrophiles (cold), Mesophiles (moderate), Thermophiles (hot), Extreme Thermophiles (very hot).
• Gases: Oxygen requirements vary (aerobes, anaerobes, facultative anaerobes, microaerophiles).
• pH: Acidophiles prefer acidic, alkalinophiles prefer basic.
• Osmotic Pressure: Halophiles thrive in high salt.
• Radiation: Phototrophs use light; UV light can be damaging to others.
• Hydrostatic Pressure: Barophiles withstand deep-sea pressures.

Symbiotic Relationships

• Mutualism: Both organisms benefit.
• Commensalism: One benefits, the other is unharmed.
• Parasitism: Parasite benefits at the host's expense.

Biofilms

• Mixed communities of microbes sharing nutrients, often forming a protective matrix.
• Quorum sensing: Communication among bacteria to coordinate activity.

Bacterial Growth and Reproduction

• Binary Fission: Simple division method for bacteria.
• Generation Time: Time it takes for bacterial population to double.
• Growth Phases in Culture: Lag, exponential, stationary, death phases.
• Logarithmic growth under optimal conditions and implications for food safety.

Conclusion

• Understanding microbial nutrition and environmental factors is crucial for applications in food preservation, clinical settings, and ecosystem management.

• Note: Refrigeration, salting, pickling are practical applications to control microbial growth based on their nutritional and environmental needs.