Methods of strain improvement
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This document discusses methods for improving microbial strains through genetic modification to increase production of commercially valuable metabolites. There are two main methods - mutation and genetic recombination. Mutation involves inducing changes in a microorganism's DNA through mutagenic agents like UV light or chemicals to generate mutants with desirable traits like higher yields, antibiotic resistance, or growth on low-cost substrates. Genetic recombination combines genetic material from two strains, such as combining a high yielding mutant with a wild type or another mutant, to further increase fermentation yields.
Methods of strain improvement
- 1. Methods of Strain Improvement
- 3. Genetic improvement of Strains • Strain: It is a genetic variant or sub-type of a microorganism. • Wild strains of microorganisms produce low quantities of commercially important metabolites. • Therefore we need genetic improvement to produce high quantities of metabolites/products. Wild strains: low yield of products Mutant strains: high yield of products
- 4. Characteristics of improved strains 1. Shorter time of fermentation 2. Capable of metabolizing low cost substrates 3. Reduced oxygen demand 4. Decreased foam formation 5. Non-production of undesirable compounds 6. Tolerance to high concentrations of carbon or nitrogen sources 7. Resistance to infections of bacteriophages
- 5. Methods of Strain improvement There are mainly two methods of strain improvement: Mutation Recombination
- 6. Mutation • Any change that occur in the DNA of a gene is referred to as mutation. This mutation result in structural change in the genome. • Mutations may be spontaneous or induced. • Spontaneous mutations occur at a very slow frequency and are not suitable for industrial purposes. • Mutations can be induced by mutagenic agents like UV light, chemicals (nitrous oxide, nitrosoguanidine, hydroxylamine).
- 7. Selection of mutants • Random screening: strain with maximum yield can be selected. • Selective isolation of mutants: There are 3 methods for selective isolation of improved strains: 1. Isolation of antibiotic resistant strain 2. Isolation of antimetabolite resistant strain 3. Isolation of auxotrophic mutants
- 8. Isolation of antibiotic resistant strain
- 9. Isolation of antimetabolite resistant strain • Antimetabolite which have structural similarities with normal metabolites can block the normal metabolic pathways and kill the cells. • Mutant strains resistant to antimetabolites can be selected for industrial purposes.
- 10. Isolation of auxotrophic mutants Auxotroph require a specific compound for its normal growth.
- 11. Genetic Recombination Combining genetic information from two genotypes. Wild strain (low yielding) + mutant strain (high yielding) = increase fermentation yield Mutant strain (high yielding) + mutant strain (high yielding) = increase fermentation yield