Cultivation of Microorganisms

Cultivation of Microorganisms

• Cultivation is the process of growing microorganisms by providing suitable environmental conditions.
• Microorganisms need metabolic energy to synthesize macromolecules and maintain chemical gradients.
• Nutrients must be in a usable form.
• Factors like nutrients, pH, temperature, aeration, salt concentration, and ionic strength influence growth.
• Three major metabolic energy mechanisms are fermentation, respiration, and photosynthesis.

Cultivation Methods

• Two key aspects for cultivation are the choice of a suitable medium and isolation of bacteria in pure culture.
• Fundamental goals in microbiological cultivation include:
  • Obtaining a crop of specific cells.
  • Determining the number and type of organisms in a sample.
  • Isolating a specific organism from a source.
• Isolation in pure culture involves isolating a single cell from other cells to maintain isolated progeny.

Plating Method

• If a small number of cells are placed on a gel medium, each cell will grow into a discrete colony.
• Agar, an acidic polysaccharide from red algae, is a good gelling agent for microbal media.

Dilution Method

• Reduces the density of microorganisms in a sample through serial dilution.
• Diluted sample is plated or inoculated to isolate single cells.
• Single cells grow into pure colonies.
• Samples from each dilution are plated or streaked on solid media.

Survival of Microorganisms in the Natural Environment

• The population of microorganisms in the biosphere is roughly constant; growth is counterbalanced by death.
• Survival depends on maintaining a pool of living organisms and successful nutrient competition.

Meaning of Microorganism Growth

• Growth means a regular increase in the organism's components (size or mass).
• In unicellular organisms, growth results in an increase in the number of individuals.

Bacterial Growth Curve

• The bacterial growth curve showcases the population dynamics in a closed system (batch culture).
• The curve shows the changes in the number of living cells over time.
• The curve has distinct phases: lag, exponential, stationary, and death.

The Lag Phase

• Bacteria adapt to the new environment.
• Increased metabolic activity, but little to no cell division.
• Duration depends on the organism and environmental conditions.
• Key processes include synthesis of enzymes, proteins, and other molecules for growth.

The Exponential Phase

• Cells divide at a constant rate, leading to exponential population growth.
• Each generation, the population roughly doubles.
• Bacteria are highly metabolically active and sensitive to antibiotics.
• Key processes include DNA replication, protein synthesis, and active metabolism.

The Stationary Phase

• Growth rate slows due to nutrient depletion and waste accumulation.
• Number of new cells equals the number of dying cells.
• Population size stabilizes.
• Key processes include adjusting metabolism to stress conditions and secondary metabolite production.

The Death Phase

• Nutrients are exhausted and toxic waste accumulates.
• Cells die at an exponential rate.
• Some bacteria form spores or enter a dormant state.
• Key processes include lysis and breakdown of cellular structures in dead cells.