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STRAIN IMPROVEMENT
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2. INDE
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•Introduction
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•Process involved
Selection of natural variants
Selection of induced mutants
The use of recombination systems
•Important characteristics for strain improvement
The selection of stable strains
The selection of strains resistant to infection
The selection of non-foaming strains
The Selection of strains which are resistant to components in the
medium
The selection of morphologically favourable strains
The selection of strains which are tolerant of low oxygen tension
The elimination of undesirable Products from a production strain
The development of strains producing New fermentation products
•Conclusion
•Reference
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3. Introductio
n:
Strain: A strain is a subgroup of a species with one or more
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characteristics that distinguish it from other subgroups of
the same species. Each strain is identified by a name, number,
or letter.
For example: E. coli strain K12, E. coli strain 0157:H7
[Ref: Jacquelyn G. Black (pg no. 242), Tortora (Pg. no. 18)]
Strain improvement:
The science and technology of manipulating and improving
microbial strains, in order to enhance their metabolic
capacities is known as Strain Improvement.
[Ref:
www.indianscience.in]
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4. Process of strain
improvement:
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Selection of
Selection of
induced
natural variants
mutants
Use of
recombinant
technology
[Ref: Stanbury, Principles of fermentation
technology
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5. Selection of natural
variants
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Keywords:
 Genetic changes
 Cell division
 Variants
 Mycelial organisms
 Heterokaryons
 Homokaryons
[Ref: Stanbury, Principles of fermentation
technology
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6. Selection of induced mutants
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• The selection of induced mutants synthesizing
improved levels of primary metabolites:
The levels of primary metabolites in micro-organisms are
regulated by Feedback control systems.
The major systems involved are feedback inhibition and
feedback repression.
[Ref: Stanbury, Principles of fermentation
technology
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FIG.1.1 The control of a biosynthetic pathway
converting precursor A to end product E via the
intermediates B, C and D.
[Ref: Stanbury, Principles of fermentation
technology
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8. Concerted
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or multivalent feedback
control:
FIG.1.2 The control of a biosynthetic pathway by the
concerted effects of products D and F on the first
enzyme of the pathway.
[Ref: Stanbury, Principles of fermentation
technology
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9. Co-operative feedback control
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FIG. 1.3 The control of a biosynthetic pathway by the co-
operative control by end products D and F.
[Ref: Stanbury, Principles of fermentation
technology
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10. Cumulative feedback control
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--- 50% ---- Inhibition of 50% of the activity of the enzyme
------ Total inhibition of enzyme activity
FIG.1.4 The control of a biosynthetic pathway by the cumulative control of
products D and F.
[Ref: Stanbury, Principles of fermentation
technology
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11. Sequential feedback control
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FIG.1.5 The control of a biosynthetic pathway by sequential
feedback control.
[Ref: Stanbury, Principles of fermentation
technology
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12. Isoenzyme control
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Fig.1.6 The control of two isoenzymes (catalysing the conversion of A to
B) by end products D and F.
[Ref: Stanbury, Principles of fermentation
technology
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13. •The isolation of mutants which do not produce
feedback inhibitors or repressors:
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Fig.1.7
Overproduction
of primary
metabolites by
decreasing the
concentration
of a repressing
or inhibiting
end product.
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14. •Examples of the use of auxotrophs for the
production of primary metabolites:
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FIG. 1.8. The control of
the aspartate family of
amino acids in C.
glutamicum.
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15. The use of recombination systems for the
improvement of industrial micro-organisms
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• Recombinant DNA techniques – In simple words, rDNA
technique can be explained as, bringing together in one
organism, genes from several organisms, has the potential for
not only increasing yields but also for producing entirely new
substances.
• Recombinant DNA technology has resulted in organisms
producing compounds which they were not able to produce
previously.
[Ref: Stanbury, Principles of fermentation
technology]
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16. The logo
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application of the parasexual cycle
•Many industrially important fungi do not possess a sexual
stage and therefore it would appear difficult to achieve
recombination in these organisms.
•However, Pontecorvo et al. (1953) demonstrated that
nuclear fusion and gene segregation could take place
outside, or in the absence of, the sexual organs.
•The process was termed the parasexual cycle and has
been demonstrated in the imperfect fungi, A. niger and P.
chrysogenum, as well as the sexual fungus A. nidulans.
[Ref: Stanbury, Principles of fermentation
technology]
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FIG. 1.9. Diagrammatic representation of the mitotic division of a
eukaryotic cell containing two chromosomes. The nuclear membrane
has not been portrayed in the figure.
[Ref: Stanbury, Principles of fermentation
technology]
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18. •Mitotic crossing over involves the exchange of distal
segments between chromatids of homologous chromosomes
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shown in Fig. 1.10.
FIG. 1.10.
Diagrammatic
representation of
mitosis including mitotic
crossing over.
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19. • Haploidization is a process which results in the equal
distribution of chromatids between the progeny of a mitosis.
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Fig. 1.11
FIG. 1.11. Diagrammatic representation of mitosis involving
haploidization.
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20. The application of protoplast fusion
techniques are cells devoid of their cell walls and may be
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• Protoplasts
prepared by subjecting cells to the action of wall degrading
enzymes in isotonic solutions. Protoplasts may regenerate
their cell walls and are then capable of growth as normal cells.
• Protoplast fusion has been demonstrated in a large number
of industrially important organisms including Streptomyces
spp. (Hopwood et al., 1977), Bacillus spp. (Fodor and Alfoldi,
1976)
[Ref: Stanbury, Principles of fermentation
technology]
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21. The improvement of industrial strains:
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Although a strain may produce a very high level of a
metabolite it would be unsuitable for a commercial process if
its productivity were extremely unstable, or if the organism's
oxygen demand were such that it could not be satisfied in the
industrial fermenter available for the process.
Therefore, characteristics of the producing organism
which affect the process may be critical to its commercial
success. Thus, it may be desirable to modify such
characteristics of the producing organism which may be
achieved by selecting natural and induced variants and
recombinants. [Ref: Stanbury, Principles of fermentation
technology]
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22. Important characteristics for strain
• The selection of stable strains
improvement
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• The selection of strains resistant to infection
• The selection of non-foaming strains
• The Selection of strains which are resistant to components
in the medium
• The selection of morphologically favourable strains
• The selection of strains which are tolerant of low oxygen
tension
• The elimination of undesirable Products from a production
strain
• The development of strains producing New fermentation
products
[Ref: Stanbury, Principles of fermentation
technology]
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23. The logoConclusion:
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selection of stable strains:
•The ability of the producing strain to maintain its high
productivity duringgenetic and molecular genetic methods a
A number of both culture maintenance and
fermentation is a very important fermentation product yields
are available to improve quality.
and other strain characteristics. The methods used for
Example: improvement of Johnson (1970)effective yet double
the Woodruff and the strain are selected a a bit
auxotrophic mutant of Micrococcus glutamicus requiring both
complicated too. The main reason of using such
homoserine and threonine and compared its lysine-producing
properties with thoseattainhomoserine auxotroph. strai that
methods is to of a an improved and stable
can be used at industrial or commercial level.
[Ref: Stanbury, Principles of fermentation
technology]
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selection of strains resistant to infection:
•Bacterial fermentations may be affected very seriously by
phage infections, which may result in the lysis of the bacteria.
•A possible method for reducing of failure due to phage
contamination is to select bacterial strains which are resistant
to the phages isolated in the fermentation plant (Hongo et
al., 1972)
[Ref: Stanbury, Principles of fermentation
technology]
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25. •The selection of non-foaming strains:
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• Foaming during a fermentation may result in the loss of
broth cells and product via the air outlet as well as putting the
fermentation at risk from contamination.
• Thus, foaming is normally controlled either by the chemical
or mechanical means, but this task may be made easier if a
non-foaming strain of the commercial organism can be
developed.
[Ref: Stanbury, Principles of fermentation
technology]
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26. The selection of strains which are resistant to
components in the medium:
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Polya and Nyiri (1966) applied this approach to the isolation
of mutants of P. chrysogenum resistant to phenylacetic acid, a
precursor of penicillin and toxic to the organism at high
concentrations.
[Ref: Stanbury, Principles of fermentation
technology]
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selection of morphologically favorable strains:
Backus and Stauffer (1955) recognized the influence of the
genetic of a strain on the morphology of P. chrysogenum in
submerged culture and its role in controlling foaming and
broth filtration characteristics
[Ref: Stanbury, Principles of fermentation
technology]
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28. The selection of strains which are tolerant of low
oxygen tension:
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Example, Mindlin and Zaitseva (1966) isolated a lysine-
producing strain which maintained its productivity under
aeration conditions which decreased the parental strain
productivity by almost a half.
[Ref: Stanbury, Principles of fermentation
technology]
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29. The elimination of undesirable products from a
production strain:
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• Athough an industrial micro-organism may produce large
quantities of a desirable metabolite it may also produce a large
amount of a metabolite which is not required, is toxic or may
interfere with the extraction process.
• An example in the penicillin-producing strains is the
elimination of the production of the yellow pigment,
chrysogenein, selection of non-pigmented mutants which made
the extraction of the antibiotic much simpler (Backus
Stauffer, 1955).
[Ref: Stanbury, Principles of fermentation
technology]
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30. The logo development of
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strains producing new
fermentation products:
• The isolation of organisms from the natural environment
synthesizing commercially useful metabolites an expensive and
laborious process.
• Therefore, means of producing novel compounds which may
be some industrial significance have been attempted.
[Ref: Stanbury, Principles of fermentation
technology]
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31. Conclusion
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A number of genetic and molecular genetic methods are
available to improve fermentation product yields and other
strain characteristics. The methods used for the
improvement of the strain are effective yet a bit complicated
too. The main reason of using such methods is to attain an
improved and stable strain that can be used at industrial or
commercial level.
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32. Reference
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• Stanbury F. Peter , 2003, Strain Improvement, Principles of
fermentation technology, Great Britain by MPG Books Ltd, Bodmin,
Cornwall, second Edition, Pg. 43-82.
•Tortora J. Gerard, 2010, Strain, Pearson Benjamin Cummings, San
Francisco, USA, tenth edition, Pg. no. 18
•Prescott M. Lansing, 2007, Strain, The McGraw-Hill Companies, Inc.,
New York,
America, seventh edition, Pg. no. 425
•Black G. Jacquelyn, 2008, Strain, JohnWiley & Sons, Inc., pg no.
242
• Net Source:
 www.cheric.org
 www.springerlink.com
 www.jhu.edu
 www.indianscience.in
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