Selection pressure in isolation of IIM

Dr.Jitender Kumar

Department of Biotechnology

HMV,Jalandhar

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ISOLATION OF INDUSTRIALLY IMPORTANT MICROORGANISMS�

• The remarkable biochemical diversity of microorganisms has been exploited by the
• fermentation industry by isolating strains from the natural environment able to produce products of commercial value.
• The so-called “golden era” of antibiotic discovery in the 1950s and 1960s, culturing soil microorganisms and screening their products, yielded the key groups of antibiotics currently in use.
• However, the lack of success in isolating producers of novel compounds in the late

History

• During 1980s and 1990s led the pharmaceutical industry to the conclusion that the pool of microbial potential had been “overfished” and, as a result, the major policy decision was taken to cease this activity.
• The industry then looked to its chemists to produce the next generation of small molecule pharmaceuticals and put its faith in the new field of combinatorial chemistry—which enables the synthesis of many thousands of compounds in a single process.

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Contribution of microbial genomics

• The contribution that microbial genomics made to the next stage of natural product exploration.
• However, the “golden age” gave rise to much of the industry and it should be remembered that antibiotics are not the only natural products produced by microorganism isolated from soil.
• Thus, the basic principles of strain isolation will be considered to give an appreciation of the origin of many current industrial producers and the basis of future developments.

Design the isolation procedure

• In some cases it is possible to design the isolation procedure in such a way that the growth of potential producers is encouraged or that they may be recognized at the isolation stage, whereas in other cases organisms must be isolated and producers recognized at a subsequent stage.
• However, it should be remembered that the isolate must eventually carry out the process economically and therefore the selection of the culture to be used is a compromise between the productivity of the organism and the economic constraints of the process.

Nutritional characteristics

• The nutritional characteristics of the organism depending on the value of the product, a process may have to be carried out using a cheap medium or a predetermined one, for example, the use of methanol as an energy source.
• These requirements may be met by the suitable design of the isolation medium.
• The optimum temperature of the organism for growth.
• The use of an organism having an optimum temperature above 40°C considerably reduces the cooling costs of a large-scale fermentation and, therefore, the use of such a temperature in the isolation procedure may be beneficial.

Factors

• The reaction of the organism with the equipment to be employed and the suitability of the organism to the type of process to be used.
• The stability of the organism and its amenability to genetic manipulation.
• The productivity of the organism, measured in its ability to convert substrate into product and to give a high yield of product per unit time.

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Industrially useful characteristic

• Industrially useful characteristic is used as a selective factor and incorporates a simple test to distinguish the most desirable types.
• Selective pressure may be used in the isolation of organisms that will grow on particular substrates, in the presence of certain compounds or under cultural conditions.

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Selective Pressure

• However, if it is not possible to apply selective pressure for the desired character, it may be possible to design a procedure to select for a microbial taxon which is known to show the characteristic at a relatively high frequency, for example,the production of antibiotics by streptomycetes.

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Screening programs

• Alternatively, the isolation procedure may be designed to exclude certain microbial “weeds” and to encourage the growth of more novel types.
• Screening programs to continue to generate new products, it is becoming increasingly more important to concentrate on lesser known microbial taxa or to utilize very specific screening tests to identify the desire.d activity

Taxonomic Databases

• During the 1980s significant advances were made in the establishment of taxonomic databases describing the properties of microbial groups and these databases have been used to predict the cultural conditions that would select for the growth of particular taxa.

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Advances in the taxonomic description

• Thus, the advances in the taxonomic description of taxa have allowed the rational design of procedures for the isolation of strains that may have a high probability of being productive or are representatives of unusual groups.
• Furthermore, whole genome sequencing of microorganisms (developed in the 2000s) can give an insight into their cultural requirements.

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Isolation methods utilizing selection��

• In this section we consider methods that take direct advantage of the industrially relevant property exhibited by an organism to isolate that organism from an environmental source.
• Isolation methods depending on the use of desirable characteristics as selective factors are essentially types of enrichment culture.
• Enrichment culture is a technique resulting in an increase in the number of a given organism relative to the numbers of other types in the original inoculum.

Environmental source

• The process involves taking an environmental source (usually soil) containing a mixed population and providing conditions either suitable for the growth of the desired type, or unsuitable for the growth of the other organisms, for example, by the provision of particular substrates or the inclusion of certain inhibitors.
• Prior to the culture stage it is often advantageous to subject the soil to conditions that favor the survival of the organisms in question. For example, air-drying the soil will favor the survival of actinomycetes.

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Subculturing

• Such subculturing may be repeated several times before the dominant organism is isolated by spreading a small inoculum of the enriched culture onto solidified medium.
• The time of subculture in an enrichment process is critical and should correspond to the point at which the desired organism is dominant.
• The prevalence of an organism in a batch enrichment culture will depend on its maximum specific growth rate compared with the maximum specific growth rates of the other organisms capable of growth in the inoculum.

Enrichment liquid culture�

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• Enrichment liquid culture is frequently carried out in shake flasks.
• However, the growth of the desired type from a mixed inoculum will result in the modification of the medium and therefore changes the selective force which may allow the growth of other organisms, still viable from the initial inoculum, resulting in a succession.
• The selective force may be reestablished by inoculating the enriched culture into identical fresh medium.

Reference

• General Microbiology – R.P. Singh (Kalyani Publication)
• General Microbiology – R.Y. Stanier
• Animal Cell Culture and Technology – Michael Butler
• Biotechnology expanding horizon by B.D.Singh
• General Microbiology by Stainier
• Biotechnology: Expanding Horizon – B.D. Singh (Kalyani Publication)
• Biophysical and Biochemical Technology – Wilson and Walker (Cambridge University Press)
• Principle of Gene Manipulation and Genomics – Primrose (Blackwell Publication)

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Thanks