The development of industrial strains, that can tolerate cultural environment and produces the desired metabolite in large amount from wild type strain is called strain improvement. The rate of production is controlled by genome of an organism. Hence the rate of production can be increased by inducing necessory changes in genome of the organism. Hence it is also called genetic improvement of microbial strain.

1. STRAIN IMPROVEMENT
TECHNIQUE (EXAM POINT OF VIEW)
Sijo.A

2. STRAIN IMPROVEMENT
 The development of industrial strains, that can tolerate
cultural environment and produces the desired metabolite in
large amount from wild type strain is called strain
improvement.
 The rate of production is controlled by genome of an
organism.
 Hence the rate of production can be increased by inducing
necessory changes in genome of the organism. Hence it is
also called genetic improvement of microbial strain.

3.  The improved strain possess the following characteristics:
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 concentration of carbon and nitrogen
sources.
7) Resistant to infection of bacteriophages.
Strain improvement can be performed in following ways.
1. Mutation and mutant selection
2. Protoplast fusion
3. Recombinant DNA technique

4. MUTATION AND MUTANT SELECTION
 Mutation is the change in the base sequence of DNA and it
changes characteristics of an organism.
 The organism exhibiting changed characteristics is called
mutant.
 The process of inducing mutation is called mutagenesis.
 Mutagenesis is a suitable method to develop new strain with
superior qualities from a wild type organism.
 Usually X-ray, UV-ray and chemical mutagens are used for
inducing variation.
 By this method, if wild type is unstable it would made into
stable.
 P.chrysogenum strain was screened from wild type culture by
culturing in a plates under biochemical test.
 It produces about 80-100 units of penicillin per ml.

5.  Another example is the production of Wisconsin 5120.
 X-ray UV-ray
P.chrysogenum X 1612 Wisconsin Q176
NTG
Wisconsin 5120
(Commercial Strain)
 N-methyl-N-nitro-N-nitroguanidine (NTG) is a commercial
strain used in industries for producing penicillin.
 It produces 2,500-5,000 units of penicillin per ml.

6. PROTOPLAST FUSION
 Protoplast are the cells devoid of cell wall.
 It is produced using lysosome (cell wall degrading enzyme) in
isotonic solution.
 Fusion of protoplast obtained from somatic cells of fungi and
bacteria is very useful to develop industrial strain in many
cases.
 Hamlin and ball fused the protoplasts of two strains of
cephalosporium acremonium using PEG (polyethylene glycol).
 The resultant protoplast produced more cephalosporin.
 Chang et.al fused the protoplast of two strains of penicillium
chrysogenum.
 The resultant protoplast produced penicillin-v.

7. RECOMBINANT DNA TECHNIQUE
 Many industrial strains have been developed using rDNA
technology .
 The gene is transferred into the harmless microbe through
DNA vector is called cloning vehicle.
 So organism become improved strain for the production of
particular product.
 Eg: the human insulin gene was transferred into the E.coli
K12 strain using cloning vehicle pBR322 . Hence E.coli K12
started to producing insulin.

8. REFERENCE
 1) Biotechnology; V.Kumeresan
 2) Biotechnology; B.D.Singh