Cultivation of Microorganisms PDF

Cultivation of microorganisms Cultivation is the process of propagating organisms by providing the proper environmental conditions. Organisms require metabolic energy to synthesize macromolecules and to maintain essential chemical gradients across their membranes. Additionally, n...

Cultivation of microorganisms Cultivation is the process of propagating organisms by providing the proper environmental conditions. Organisms require metabolic energy to synthesize macromolecules and to maintain essential chemical gradients across their membranes. Additionally, nutrients must be provided in metabolically accessible form. Microorganisms vary widely in their nutritional demands and their source of metabolic energy. Factors that must be controlled during growth include the nutrients, PH, temperature, aeration, salt concentration, & ionic strength of the medium. The three major mechanisms for generating metabolic energy are fermentation, respiration & photosynthesis. At least one of these mechanisms must be employed if an organism is grow this is essential in microbiology for research, medical diagnostics, industrial applications, and biotechnology. Cultivation methods: For cultivation of microorganisms two things must be considered; the choice of a suitable medium & the isolation of a bacteria in pure culture. Generally, these are fundamental goals in microbiological cultivation : 1. To raise a crop of cells of a particular species. 2. To determine the number & type of organism present in a given material. 3. To isolate a particular type of organism from a natural source. Isolation of microorganisms in pure culture: To do this, a single cell must be isolated from all other cells & cultivated in such a manner that its collective progeny also remain isolated. Several methods are available Plating method: If few enough cells are placed in or on a gelled medium, each cell will grow into an isolated colony. The ideal gelling agent for most microbal media is agar, an acidic polysaccharide extracted from certain red algae. Dilution method: the dilution method reduces the density of microorganisms in a sample through serial dilution. The diluted sample is plated or inoculated to isolate single cells, each of which can grow into a pure colony The suspension is serially diluted & samples of each dilution are plated or streaked on solid media. Isolation of microorganisms in pure culture 1 Survival of microorganisms in the natural environment: The population of microorganisms in the biosphere is roughly constant; growth is counterbalanced by death. The survival of any microbial group within its environment is determined by maintenance of a pool of living nutritional deprivation & by successful competition for nutrients. The meaning of growth: Growth is the regular increase in the sum of all components of an organism. This means that an organism, whether multicellular or unicellular, increases in size or mass over time as its cellular components increase. In unicellular microorganisms (such as bacteria), growth involves the duplication of cells, resulting in an increase in the number of individuals in the population or culture. The growth curve: The bacterial growth curve represents the population dynamics of bacteria growing in a closed system (batch culture). It describes changes in the number of living cells over time when bacteria are provided with a fixed amount of nutrients and environmental conditions. The curve has distinct phases: 2 1- The lag phase: Bacteria adapt to the new environment and prepare for active division. Metabolic activity increases, but there is little to no cell division. Duration depends on the organism and environmental conditions (e.g., nutrient availability, temperature). Key Processes: Synthesis of enzymes, proteins, and other molecules required for growth. 2-The Exponential phase: Cells divide at a constant rate, resulting in exponential population growth. The population doubles during each generation time. Bacteria are most metabolically active and sensitive to antibiotics and environmental changes. Key Processes: DNA replication, protein synthesis, and active metabolism. Maximum utilization of available nutrients. 3-The maximum stationary phase: Growth rate slows as nutrient depletion and waste accumulation occur. The number of new cells equals the number of dying cells, leading to a stable population size. Key Processes: Metabolism adjusts to stress conditions (e.g., secondary metabolite production like antibiotics).. 4-The decline or death phase: Nutrients are exhausted, and toxic waste products accumulate. Cells die at an exponential rate. Some bacteria may form spores or enter a dormant state to survive harsh conditions. Key Processes: Lysis and breakdown of cellular structures in dead cells. Maintenance of cells in the exponential phase: Cells can be maintained in exponential phase by transferring them repeatedly into fresh medium of identical composition while they are still growing exponentially. The meaning of death: For microbial cells, death means the irreversible loss of the ability to reproduce (growth & division). *The test of death is the culture of cells on solid media; a cell is considered dead if it fails to give rise to a colony on any medium. Then the reliability of the test depends upon choice of medium & conditions. 3