Methods of strain improvement

Wild strains of microorganisms produce low quantities of commercially important metabolites.
Therefore we need genetic improvement to produce high quantities of metabolites/products.

1. Methods of Strain Improvement

3. GeneticimprovementofStrains
•Strain:Itisageneticvariantorsub-typeofamicroorganism.
•Wildstrainsofmicroorganismsproducelowquantitiesof
commerciallyimportantmetabolites.
•Thereforeweneedgeneticimprovementtoproducehighquantitiesof
metabolites/products.
Wildstrains:lowyieldofproducts
Mutantstrains:highyieldofproducts

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 spontaneousor induced.
•Spontaneous mutations occur at a very slow frequency and are not
suitablefor industrial purposes.
•Mutationscan be inducedby 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
•Antimetabolitewhichhavestructuralsimilaritieswithnormal
metabolitescanblockthenormalmetabolicpathwaysandkillthe
cells.
•Mutantstrainsresistanttoantimetabolitescanbeselectedfor
industrialpurposes.

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