mb-m2

Growth and Cultivation of Microorganisms

Bacterial Reproduction

  • Bacteria reproduce asexually through a process known as binary fission.

  • The reproduction results in exponential growth (logarithmic), leading to a rapid increase in population.

  • Time required for cell division and population doubling:

    • 0 hrs: 1 cell

    • 0:20 hrs: 2 cells

    • 0:40 hrs: 4 cells

Phases of Bacterial Growth

1. Lag Phase

  • Minimal cell division occurs; population remains stable.

  • Cellular activities include:

    • Growth in cell volume or size.

    • Synthesis of enzymes and proteins.

    • Increase in metabolic activity.

2. Log Phase

  • Also known as exponential/geometric growth phase.

  • Cells begin dividing significantly, entering a period of logarithmic increase.

  • Cellular reproduction is highly active, and the generation time reaches a constant minimum.

  • Factors limiting continuous growth:

    • Nutrient exhaustion.

    • Accumulation of inhibitory metabolites.

    • Limited biological space.

3. Stationary Phase

  • Growth rate slows due to:

    • Depletion of available nutrients.

    • Production of toxic metabolites.

  • New cells produced equal the number that die, resulting in a steady state.

4. Decline Phase

  • Referred to as the death phase.

  • Characterized by an exponential decrease in the number of bacteria.

  • Irreversible loss of the ability to reproduce.

Bacterial Growth Requirements

1. Cultivation

  • The process of propagating microorganisms in proper environmental conditions.

  • Requirements include:

    • Proper elements.

    • Sufficient nutrients.

    • Adequate metabolic energy.

2. Factors to Control

  • Key factors include:

    • Nutrient composition.

    • pH levels.

    • Temperature settings.

    • Aeration.

    • Salt concentration.

    • Ionic strength of the growth medium.

Sources of Metabolic Energy

1. Fermentation

  • Characterized by substrate phosphorylation.

  • ATP formation is not coupled with electron transfer.

2. Respiration

  • Requires an oxidizing agent, typically oxygen (O2), but can include CO2, sulfate, and nitrate.

  • Involves the chemical reduction of the oxidant using a series of electron carriers.

  • Acceptable electron donors can be organic (like lactic acid) or inorganic (like hydrogen gas).

3. Photosynthesis

  • Process somewhat similar to respiration.

  • Involves a photochemical process to create the reductant and oxidant through a series of electron carriers.

Chemical Requirements for Microbial Growth

  • Carbon: Derived from organic material (proteins, carbohydrates, lipids) or CO2.

  • Nitrogen: Critical for amino group formation in amino acids; often assimilated as NH3 (ammonia).

  • Sulfur: Needed for coenzymes; sourced from sulfate and hydrogen sulfide.

  • Phosphorus: Key component of ATP, nucleic acids, coenzymes, and phospholipids, often sourced in phosphate form.

Mineral Sources

  • Magnesium (Mg2+): Part of chlorophyll molecules.

  • Iron (Fe2+): Essential for cytochromes and peroxidases.

  • Calcium (Ca2+): Necessary for Gram-positive cell wall structure.

  • Sodium (Na+): Essential for marine organisms.

  • Other minerals include: Mn2+, Mo2+, Co2+, Cu2+, Zn2+.

Physical Requirements

1. Temperature

  • Optimal temperature ranges vary for different microorganisms.

2. pH

  • Bacteria have specific pH preferences that impact their growth.

3. Gaseous Requirements

  • Most organisms benefit from O2, enhancing their metabolism.

  • O2 can also produce toxic substances (H2O2, superoxide radicals).

    • Some microorganisms produce enzymes to mitigate these effects:

      • Superoxide dismutase (SOD): Converts superoxide radicals to less harmful substances.

      • Catalase: Breaks down hydrogen peroxide.

4. Osmotic Pressure

  • Halophiles: Require high salt concentrations.

  • Osmophiles: Require high osmotic pressure conditions.