Prasanna

Learninsta presents the core concepts of Microbiology with high-quality research papers and topical review articles.

Screening of Industrially Important Microorganism

Isolation of industrially important microorganisms

Success of fermentation depends upon the isolation of microorganism. The microorganisms are isolated from their natural habitats like soil, lakes, river mud or even in unusual habitats or environments such as extreme cold, high altitude, deserts, and deep sea and petroleum fields and are tested directly for the product formation and isolated or it can be genetically modified.

Different types of microorganisms are isolated by different methods. Different microbes with desired activity are isolated using various culture techniques. The next step after isolation of microorganisms is the selection or screening. For the successful fermentation process, selection of microorganisms is the prime important step. Screening includes primary screening and secondary screening.

Primary screening:
The elementary steps that are performed to select the desired organisms and eliminate the undesirable organisms are termed as primary screening. Methods such as crowded plate technique, auxanography and enrichment culture technique are some of the techniques used in primary screening. For screening of antibiotic producing organisms crowded plate technique is described here,

Crowded plate technique

1. Soil is serially diluted
2. The serially diluted sample is spread on the nutrient agar plates
3. The plates are incubated and the agar plate having 300 to 400 colonies are observed for antibiotic producing activity
4. The ability of a colony to exhibit antibiotic activity is indicated by the presence of a zone of inhibition surrounding the colony
5. The technique is improved by using test organism
6. The antibiotic produced by the organisms in the soil may inhibit the growth of test organism
7. The formation of inhibitory zones around certain colonies indicates their antibiotic sensitivity
8. The diameter of the zones of inhibition is measured in millimeters. Crowded plate technique is depicted in the diagram (Figure 6.3).

Enrichment isolation

The process of enrichment provides a suitable condition to support the growth of microorganisms. It allows the growth of the specific microbe while inhibiting the other non-target microbe. The growth of target microorganisms is enriched by providing sole carbon source.

For screening microorganisms degrading the compound, different inhibitors are employed which have the ability to block a specific metabolic pathway of the non-target microbe.

pH and temperature are also adjusted favoring the growth of desired microorganisms. Soil Calcium carbonate enrichment technique is used for isolation of secondary metabolite producing microorganisms (actinomycetes).

Secondary screening

It is very useful in sorting out microorganisms that have real commercial value from many isolates obtained during primary screening.

1. As primary screening allows the detection and isolation of microorganisms which posses, potentially interesting industrial applications. It is further followed by secondary screening, to check the capabilities and gain information about these organisms.

2. Through primary screening only few or many microorganism that produce a industrially important product, are isolated. The information about the product formed is very less. So, through secondary screening, further sorting out is performed. In this method, only microorganisms with real commercial
value are selected and those that lack the potential are discarded.

3. Secondary screening should yield the types of information which are needed in order to evaluate the true potential of a microorganisms industrially usage.

4. Secondary screening may be qualitative and quantitative in its approach.

5. It is done by using paper, thin layer or other chromatographic techniques.

6. The product’s physical, clinical, and biological properties are determined.

7. It detects gross genetic instability in microbial cultures.

8. It gives information about the number of products produced in a single fermentation.

9. It determines the optimum conditions for growth or accumulation of a product associated with particular culture.

10. It gives information about the different components of the fermentation medium.

11. It helps in providing information regarding the product yield potential of different isolates.

12. It reveals whether microorganisms are capable of a chemical change or it destroys their fermentation product.

There are various methods employed for secondary screening which includes test conducting on petridish containing solid media or by using flasks or small fermentors containing liquid media, giant colony technique, and filtration method liquid medium method (using Erlenmeyer flask). Here giant colony technique is explained in detail.

Giant Colony Technique

The Streptomyces culture is inoculated onto the central areas of petriplates containing a nutritious agar medium or they are streaked in a narrow band across the centre of plates. The plates are then incubated until growth and possibly, sporulation have occurred. Strains of micro organisms to be tested for possible
sensitivity to the antibiotics (the test organisms) are then streaked from the edges of the plates up to but not touching the Streptomycete growth.

The plates are further incubated to allow the growth of the test organism. The growth of the test organism inhibited by antibiotic in the vicinity of the Streptomycete is then measured in millimeters. These Streptomycetes that have produced antibiotics with observable microbial inhibition spectrum are retained for further testing (Figure 6.4).

The microbes used in the industrial microbiology should have following characters.

1. The strain should be a high-yielding strain.
2. The strain should have stable biochemical and genetical characteristics.
3. It should not produce undesirable substances.
4. It should be easily cultivated on large scale.

The strain should be in pure culture, free from other microorganisms including Bacteriophages. These characters are screened for the production of desirable products from microorganisms.

Learninsta presents the core concepts of Microbiology with high-quality research papers and topical review articles.

Industrially Important Microorganisms and their Products of Microbiology

Microorganisms have the powerful capacity to produce numerous products, during their life cycle. Flowchart 6.1 shows the production of valuable metabolic products during the growth of microorganisms on a suitable medium under controlled environmental conditions. Microbial products are often classified as primary and secondary metabolites.

Primary metabolites consist of compounds related to the synthesis by microbial cells in the growth phase. Primary metabolites such as amino acids, vitamins, enzymes, organic acids and nitrogenous bases are produced by wide variety of microorganisms. These primary metabolites are essential for the growth of microorganisms and they are produced during Logarithmic phase.

Secondary metabolites do not play a role in development, growth and reproduction of microorganisms. They are produced at the end of growth phase near stationary phase. They usually accumulate during the period of nutrient limitation or waste product accumulation that follows the exponential phase. These compounds have no direct relationship to the synthesis of cell materials and normal growth.

They are the end products of the primary metabolism. Products such as steroids, alkaloids, antibiotics are secondary metabolites. Excessive production of the primary and secondary metabolites produced by the microorganisms are useful in the large scale in industrial production. Unlike primary metabolites, secondary metabolites are produced in small quantities and their extraction is difficult (Figure 6.2).

Some industrially important products are,

• microbial cells (living or dead), microbial biomass and components of microbial cells
• microbial metabolites
• intracellular or extracellular enzymes
• modified compounds that has been microbiologically transformed, and recombinant products through the DNA recombinant technology. (Table 6.1 shows some industrially important microorganisms)

Industrially important microorganisms

The industrial production of commercial products is carried out by fermentation process. The term fermentation is defined scientifically in a strict sense as a biological process that occurs in the absence of oxygen (anaerobic).

In industrial sense any process mediated by or involving microorganisms in which a product of economic value is obtained is called fermentation. The term Industrial fermentation also means large scale cultivation of microorganisms even though most of them are aerobic.

There are many microbiological processes that occur in the presence of air (aerobically) yielding incomplete oxidation products.
Examples:

1. The formation of acetic acid (vinegar) from alcohol by vinegar bacteria
2. Citric acid from sugar by certain molds such as Aspergillus niger. These microbial processes are often referred to as fermentations, although they do not decompose in the absence of air.

Learninsta presents the core concepts of Microbiology with high-quality research papers and topical review articles.

Food Microbiology of Curd and its Uses

Curd is a dairy product obtained by curdling or coagulating milk with rennet or an edible acidity substance such as lemon juice or vinegar and then draining off the liquid portion called whey milk that has been left to sour (raw) milk alone or pasteurized milk with added lactic acid bacteria or yeast (Example: Lactobacillus acidophilus) will also naturally produce curds and sour milk cheese is produced this way.

The increased acidity causes the milk protein (casein) to tangle into solid masses or curds in cow’s milk, 80% of the protein and caseins (Figure 5.8).

Uses

• Enhances healthy digestion
• improves immunity
• For stronger bones and teeth
• Helps to lose weight
• Beauty benefits of curd – for healthy and Radiant skin, prevent premature wrinkles remove dark spots and dandruff.