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= Strain Development Techniques = A strain is a group of species with one or more characteristics that distinguish it from other subgroups of the same species of the strain. Strain development is the process of the introduction of new genetic properties in microbial strains to improve their potentials for various biotechnological applications. Various techniques are used to increase the productivity of the strain, regulate the activity of the enzymes, increase the permeability, to change unused co-Metabolites Introducing new genetic properties into the organism by Recombination DNA technology / Genetic engineering.

Techniques

 * Mutant Selection
 * Recombination
 * Recombinant DNA Technology

Mutation Selection
Many Mutations bring about marked changes in the biochemical characters of practical interest these are called Major Mutations which can be used in strain development. Example: Streptomyces griseus Streptomycin - Mannosidostreptomycin Streptomyces aurofaciens (S-604) _ Produce 6-dimethyl tetracycline in place of Tetracycline

Reports on strain improvement by mutation
° Karana and Medichlera (2006)- lipase from Aspergillus japonicus MTCC 1975 - mutation using UV, HNO2, NTG showed 127%, 177%, 276% higher lipase yield than parent strain respectively. ° First superior penicillin mutant producing mutant., Penicillium chrysogenum X-1612, was isolated after X-ray mutagenesis.

Isolation of mutants

The methods mentioned below are used to detect and isolate mutants for strain development.


 * Replica Plating Technique
 * Resistance Selection Method
 * Substrate Utilization Method
 * Carcinogenicity Test

Replica PlatingTechnique
Lederberg and Lederberg (1952) have given the replica plating technique. This technique is used to detect autotrophic mutants that differentiates between mutants and wild type strains on the basis of the ability to grow in the absence of amino acid.

Resistance Selection Method
It is the other approach for the isolation of mutants. Generally, the wild type cells are not resistant to either antibiotics or bacteriophages. Therefore, it is possible to grow the bacterium in the presence of the agent (antibiotics or bacteriophages) and look for survivors.

Substrate Utilization Method
This method is employed in the selection of bacteria. Several bacteria utilize only a few primary carbon sources. The cultures are plated to medium containing an alternate carbon source. Any colony that grows on the medium can use the substrate and are possibly mutants. These can be isolated.

Carcinogenicity Test
To identify the environmental carcinogens that cause mutation and induce cancer in organisms. It is based on the potential of carcinogens and testing for mutagenicity in bacteria.

Recombination
It’s the formation of new gene combinations among those present in different strains used for both genetic analysis and strain development. Recombination may be based on transformation, Conjugation, cross over and transduction, protoplast fusion, etc.

Recombination in microorganisms occurs through three parasexual processes: conjugation, transduction, and transformation. Internal genetic rearrangements can also occur via translocatable DNA segments (insertion sequences ). Conjugation involves transfer of DNA via cell-to-cell contact. Transduction occurs from host cell to recipient cell via mediation by bacteriophage. Transformation involves uptake and expression of naked DNA by competent cells. Competence occurs naturally but can also be induced by changes in the physical and chemical environment. In the laboratory, it can be induced by cold calcium chloride treatment, protoplasting, electroporation and heat shock.

As mentioned above, genetic recombination was virtually ignored in industry, mainly due to the low frequency of recombination. However, use of protoplast fusion changed the situation markedly. After 1980, there was a heightened interest in the application of genetic recombination to the production of important microbial products such as antibiotics. Today, frequencies of recombination have increased to even greater than 10 in some cases, and strain improvement programs routinely include protoplast fusion between different mutant lines. The power of recombination was demonstrated by Yoneda who recombined individual mutations, each of which increased α-amylase production by two- to seven-fold in Bacillus subtilis. A strain constructed by genetic transformation, which contained all five mutations, produced 250-fold more α-amylase than the starting strain.

Recombinant DNA Technology
This technology involves the isolation and cloning of genes of interest, production of the necessary gene constructs using appropriate enzymes, and then transfer and expression of these genes into a suitable host organism. This technique has been used in the production of recombinant proteins and metabolic engineering.

== Applications ==


 * It is used for large scale production of vaccines, enzymes, interferon, growth factors, blood clotting factors.
 * In the field of Microbiology to improve the microbe’s productivities or characteristics.
 * Treatment of genetic diseases like SCID by rDNA technology.
 * Production of medically useful biological products like insulin.