Immobilization figure, screening, types of screening

2. Screening – It refers to the isolation of only those microorganisms which are of interest
from among a large population of microbes. They are mainly of two types:
Primary and Secondary Screening
Primary Screening : The effective screening must in one or few steps
which allow the discarding of many valueless microorganisms, while at
the same time allowing the easy detection of the small percentage of
useful microorganisms that are present in the population.
Secondary Screening : As primary screening allows detection and
isolation of microorganisms that possess potentially interesting industrial
applications. This is usually followed by a secondary screening to further
test the capabilities of and gain information about these organisms.

5. Types of Primary Screening
• Crowded-plate technique – Natural microbial source such as soil is diluted to
provide a cell concentration such that aliquots spread, sprayed or applied in some
manner to the surfaces of agar plates will yield colonies not touching neighbouring
colonies.
• An alternative procedure for detecting organic acid production involves incorporation
of calcium carbonate in medim so that organic acid production is indicated by cleared
zone of dissolved calcium carbonate around the colony.
• Screening approach has also been employed extensively in search for the
microrganisms capable of producing useful antibiotics.
• The simplest screening technique for antibiotic procedures is the “crowded plate”
procedure.
• Colonies producing antibiotic activity are indicated by an area of agar around the
colony that is free of growth of other colonies. Such a colony is subcultured to a
similar medium and purified by streaking before making stock cultures.

7. Improvement of crowded technique
Antibiotic screening is improved, therefore, by incorporation into the procedure of “test
organism”, that is an organism us as an indicator for the presence of specific antibiotic
activity.
A suspension of test organism is then sprayed or applied in some manner to the surface of
the agar, and then plates are further incubated to allow growth of the test organism.
When volatile substrates such as hydrocarbons, low molecular weight alcohols, and
similar carbon sources are being considered.
The dilutions from a microbial sources are applied to plates of agar media containing all
nutrients but the specific substrate and the specific substrate is placed in the lid of
petriplate after inversion of the plate.
Enough vapours from the volatile substrate rise to the surface of the agar within this
closed atmospheric to provide the specific nutrient for the microorganism.

13. Secondary Screening
 Secondary screening allows the further sorting out of those
microrganisms that have real value for industrial processes and
discarding of those lacking this potential.
 Secondary screening is conducted on agar plates, in flasks or small
fermenters containing liquid media, or combination of these
approaches.
 Liquid culture provides a much better picture of the nutritional
physical, and production of responses of an organism to actual
fermentation production conditions.

14. Secondary screening can be qualitative
and quantitative in its approach
Qualitative approach – eg. Spectrum or range of microorganisms which is sensitive to a
newly discovered antibiotic.
Quantitative Approach – This tells us about the yields of antibiotic which can be
expected when the microorganism is grown in various differing media.
Secondary screening should yield types of information which are needed in order to
evaluate the true potential of a microorganism for industrial usage.
Secondary screening should determine whether a more economical process is
possible.
To determine whether a product actually is newly discovered sompound, we can utilize
paper, thin layer or other chromatographic procedures to compare the product with known
compounds.
Secondary screening should detect real differences in product yiels potentials among
various isolates.

15.  Secondary screening should reveal whether there are pH, aeration, or other
critical requirements associated with particular microorganisms, both for the
growth of the organism and for the formation of chemical products.
 Screening should show whether certain medium constituents are missing or
possibly are toxic to growth of the organism, or its ability to accumulate
fermentation products.
 It should show something of chemical stability of the product and product
solubility.
 It should determine whether the product has simple, complex, or even a
macromolecular structure.
 It should show whether the product possesses physical properties such as U.V.
light absorption or fluorescence, or chemical properties that can be employed
to detect compound.

16.  Certain kinds of fermentation products, determinations should be made as to
whether gross animal, plant or human toxicity can be attributed to the
fermentation product, particularly if it is to be utilized in disease treatment.
 Secondary screening should reveal whether a product resulting from a
microbial fermentation occurs in the culture broth in more than one chemical
form, and whether it is an optically or biologically active material.
 Secondary screening should reveal whether microorganisms are able to
chemically alter or even destroy their own fermentation products. Thus, a
microorganism might produce a “racemase” enzyme that will change the L-
configuration of an amino acid product to a mixture of the D and L- isomer of
being little biological value.

17. Thank You