Branches of Microbiology

Branches of Microbiology

Micro-organism are present everywhere in nature  and this micro-organism has a great effect on other life form like human being,plants and animals in several ways.The effect of micro-organism to the environment may be desirable or undesirable.These bacteria show wide range of activity and diversity.On basis on taxonomic characters and application of micro-organism in different fields the microbiology is further divided into different branches.

On basis of Taxonomic characters  Microbiology is further divided into the following branches

  1. Bacteriology
  2. Mycology
  3. Phycology
  4. Parasitology
  5. Immunology
  6. Virology

1. Bacteriology

Bacteriology is a branch of Microbiology that deals with study of Bacteria.This Bacteria are prokaryotic, unicellular in nature.Their mode of multiplication is by Binary fission.Bacteria can be parasitic or can be free living in atmosphere.The nuclear material is not bound to nuclear membrane.This bacteria may be motile or non-motile.They may vary in their shape like rod,spiral or cocci and they may be aerobic,non-aerobic or facultative anaerobic in nature.On the basis of mode of nutrition some bacteria may have autotrophic or hetrotrophic mode of nutrition.


Mycology is a branch of microbiology that deals with study of Fungus.This fungus cells are eukaryotic in nature the nuclear material is surrounded by Chitin or cellulose or both. This fungal cells are non-photosynthetic and chemoorganotrophic in nature.These fungal cells are divided into two types and that is yeast and molds.

  • Yeast -The yeast cell may occur in single cell or pseudomycelium form.The mode of reproduction is by budding or by Spore formation.Yeast are also know as Ascomycetes and this yeast cells may be oval,rod or spherical in shape.
  • Molds-The molds grow in form of multi-cellular filamentous structure called as hyphae. This hyphae may be septed or non-septed. They can reproduce by both means of sexual and asexual mode of reproduction.

3. Phycology

Phycology is a branch of microbiology that deals with the study of algae.They are photosynthetic,eukaryotic,and multi cellular organism.

4. Parasitology

It is a branch of biology that deals with the study of parasites. This branch mainly include the study of three major group of bacteria parasitic protozoa,parasitic worms, and arthropods.In the relationship between host and parasite is also studied.This parasites may be unicellular or multi-cellular. This parasites are mainly responsible for causing infection in humans and animals.


Immunology is a branch of microbiology that deals with the study of Immune system of all organism specially human being and animals.In this branch of microbiology the relationships between host body,pathogen and immunity is studied.

6. Virology

This branch of microbiology deals with the study of Viruses.Viruses are very small ultra-microscopic in nature and they are visible through electron microscope.Viruses are metabolically inert and are completely dependent on host cell for replication.Viruses are capable to infect all types of cells from a bacteria to a human.It contain only one type of nucleic acid that is either DNA or RNA.

On the basis of taxonomic characters these were some branches of microbiology.

Their are some major applied branches of microbiology.

Applied Branches of microbiology are as follows

  1. Air Microbiology
  2. Water Microbiology
  3. Sewage Microbiology
  4. Soil Microbiology
  5. Food microbiology
  6. Milk Microbiology
  7. Industry Microbiology
  8. Medical Microbiology
  9. Geomicrobiology
  10. Biotechnology

1 Air Microbiology

Micro-organism spread through air from one place to another.The micro-organism are present everywhere in nature and the micro-organism present in air are responsible for contamination of food or transmission of disease.The diseases such as tuberculosis,Influenza , and some plant and animal fungal disease etc spread via air.So it is important to study specific area for controlling  and preventing the spread of some microbes and this all studies related air and microbes is carried out in this branch.

2.Water Microbiology

Water is the most important thing that is required for a life form to survive.So the water used should pure ,free of chemicals as well as free from disease causing organisms.Their are Municipal water purification units that are used to purify water and this quality of water is checked by examination of water.Water microbiology is used here to check whether the water is potable or not.Supply of good quality of water is very important as water can be a source for transmission of various disease.

3.Sewage Microbiology

Sewage water is the used water of the community.This sewage water contain different chemicals as well as pathogenic or non-pathogenic micro-organism.If the sewage water is kept untreated before disposal it can cause harm to the environment as well as any life form.In sewage microbiology the sewage water is treated by use of some techniques,chemicals and some useful bacteria.

4.Soil Microbiology

Soil is supposed to be source of many micro-organism.Study of micro-organism present is soil is called as soil microbiology.The soil becomes fertile if their are useful micro-organism present in soil.These micro-organism involve transformation of elements important for growth of crops as well as degradation of organic matter to simple form.The bacteria also help in fixation of atmospheric nitrogen for growth of plants.The soil is a major source of antibiotic producing micro-organism.In soil we can find variety of micro-organism like bacteria,fungi,viruses and protozoa.Thus study of soil microbiology is very important.

5.Food Microbiology

Food microbiology is a important branch as it deals with study of association of micro-organism with food.Micro-organism deal with food in two ways one it can spoil the food and spread the infection or disease.Secondly it can used some substrate and convert into a product that is fermentation. Micro-organism can ferment the substrate and form the product like curd, Idli ,Cheese, Butter etc.If the quality of food is not check properly it may result in spread of food born diseases.So the  study related fermentation and quality check of food is important

6.Milk Microbiology

Milk is a rich and one of the best food and so their are chances of contamination of milk.If the milk get contaminated their are great chances of spoilage of milk.Milk is used on large scale in dairy industry where various products like cheese,butter,ghee,curd are prepared.Useful bacterial present in milk helps in preparation of various milk product where as  harmful bacteria can spoil everything.The food born diseases can spread through milk if it is not sterilised properly.So it is important to study sterilization of milk,preparation of various milk product as well as prevention of milk born diseases.

7.Industrial Microbiology

Industrial microbiology is a branch of microbiology where large amount of substrate are converted to economically important product by use of micro-organism.Micro-organism are used in many industries on large scale for production of various product like antibiotics,beverages,Vaccines,proteins as well as food industries.Therefore the study of such organism that are be useful in industries for production of economically important product is very important

8.Medical Microbiology

In nature their are many useful micro-organism as well as many harmful micro-organism.Harmful in sense disease causing micro-organism.In this branch the study is carried out on the causative agent of disease, Identification,pathogenecity, prevention and cure of disease.It also deals with antibiotics.


This branch of microbiology studies the relation of microbes with some geological substances like formation of coal,mineral and gas formation as well as recovery of minerals from low grade ores.It also helps in degradation of hydrocarbon accumulated in nature in form of pollutants.Micro-organism are used for removal of oil spills in the ocean by degradation of hydrocarbon and save the aquatic life near the oil spill.


Biotechnology is a branch of biology that deals with the study of technology and any life form like microbes,plants animals in the sense to improve quality of life and develop new technology.It involves techniques like plant tissue culture ,Animal tissue culture,Recombinant DNA technology And genetic modification of organism.



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Strain Improvement of Micro-organisms Used in fermentation.

Strain Improvement of Micro-organisms Used in fermentation.

In industries the micro-organism are selected by using various screening procedure.The strain which is selected on industrial scale for commercial production of a product should be able to produce high yield of product constantly.This constant high yield of product makes the fermentation economic as well as face the competition with other industries.For obtaining high yield of product the industries carry out strain improvement as well as strain selection programs continuously. During the strain improvement program various parameters are adjusted to increase product yield.

The parameters like pH,temperature,media components,aeration,agitation,innoculum levels are adjusted and variation in this levels are tested for increasing yield of product.But however this change in parameters doesn’t give large yield and effective results by microbial strains used. The fermentation organism which is being used in fermentation can give constantly increased high yield of product by use of strain improvement program and selection of the most efficient strain for production of product on industrial scale.

The strain improvement of micro-organism used in fermentation process is done by altering the genetic make up of strain and selecting the most efficient strain from various improved strain and result in increased yield of product.After the strain improvement program the selected strain should be genetically stable.The selected strain should produce desirable product in large amount and undesired product in less quantity.Before caring out the mutation program the selected strain should be efficient under all optimum  fermentation condition.The selected strain is exposed to various strain improvement programs and the strain giving high yield of product is selected among all tested strains.The strain that is selected should be able to produce high amount of yield as compared to the original unaltered parent strain.

The genetic make-up of selected strain can be changed by using following methods:-

  1. Genetic recombination or gen transfer.
  2. Mutation
  3. Genetic engineering

1] Genetic recombination or gen transfer

The genetic recombination mechanism exist in different strains of bacteria and some actinomycetes. In genetic recombination mechanism transfer of a gene from one type of strain to other type of strain of micro-organism takes place.This gene transfer takes place by conjugation,transformation or transduction. Gene transfer can be carried out by protoplast fusion of two different efficient strains and new improved strain can be developed.

The fungal strain undergo para sexual cycle and mitotic cell division which is very important and of great value in strain improvement.Genetic Breeding is also possible in different genera of yeast.Thus by using genetic recombination and gene transfer technique it is possible to combine the desired characters from two different strains of same species by interstrain breeding and obtain a efficient strain that is able to produce high yield of product on industrial scale.

2] Mutation

Mutation can be defined as change in genetic structure of micro-organism.The ability of micro-organism to produce a desired product can be enhanced by a mutation process.In mutation process the most stable and efficient strains are exposed to mutagenesis by using different mutagenic agents.The mutagenic agents like ionization,ultraviolet radiation,acids,and alkalies are used in mutation.Result of mutation obtain should be increased in yield of desired product and decreased yield of undesired product.The mutagenic agents are used in such concentration that maximum number of cells die due to mutagenic agents and only the that are capable to carry out mutation and have the capacity to tolerate the levels of mutagenic agents are able to survive.From the survived cells the cells which are undergone mutation and have the capacity to produce high yield of fermented product is selected.

The selection of a mutated cell is a very difficult task. Whenever the microbial cells are subjected to mutation their are two possibilities and that are the mutation occurred may be major mutation or minor mutation. The strain undergone desired mutation should be carefully selected,isolated and maintained properly.The selected mutant strains with altered morphological and biochemical characters are now the strain that produce high yield of desired product.The improved selected strain should be tested with laboratory scale experiments followed by pilot plant experiments and then further used on commercial scale.The finalized strains are selected,purified and maintained.All the test and experiments should be carried out with high accuracy as these procedures are time consuming and expensive.Further when these strains are used on industrial scale a proper record of yield produce should be maintained as minor changes should be noted.

3] Genetic engineering

Genetic engineering technique is the most successful technique used for strain improvement programs on industrial scale.It is also called as Recombinant DNA technology and in this process their is alteration of genetic characters of cells and hence result in change in phenotypic character of cell.This  In this technique a desired type of gene is introduced from one microbial cell to other microbial cells by using  cloning vectors,like plasmids ,phages or cloning vectors.A specific and desired character of a microbial cells can be introduced in the selected strain to improve the yield of product.


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Screening Techniques

Screening Technique

The screening techniques are generally carried out in two stages.

  1. Primary Screening
  2. Secondary Screening

1. Primary Screening

Detection and isolation of industrially important micro-organism from mixed population using simple techniques is called as primary screening techniques.In primary screening technique simple methods are used to detect valuable micro-organism based on certain biochemical characters of microbes.Generally the sample is collected,serially diluted and isolated on suitable agar medium by specific technique.

Here are some examples of primary screening

a] Screening of antibiotic producing micro-organism.

In screening of antibiotic producing micro-organism a crowded plate technique is used.Here source used for screening of micro-organism is generally soil.The sample of soil used is serially diluted in sterile distill water.The suitable amount of diluted sample that is 0.1 ml is taken by a sterile pipette and spreaded or sprayed on suitable sterile agar medium in sterile conditions.This inoculated medium is incubated in incubators at room temperature for 24 to 48 hours.This cultures are in incubated at room temperature because the source of micro-organism is soil and room temperature is suitable for growth of this microbes.The agar plates which have 300 to 400 colonies are selected.The plates having well isolated colonies are used for further studies as the well isolated colonies show the clear zone due to production of antibiotic and inhibition of growth of other micro-organism .These antibiotic producing colonies are further sub-cultured on fresh desired media and sub-cultured growth is purified by re-streaking.The stock cultures are maintained and used for further studies.

b] Screening of organic acid or amine producing micro-organism

In screening of organic acid or amine producing micro-organism the source used may be soil,milk or milk product.The source taken is diluted by serial dilution technique in sterile distill water and spread inoculated on agar medium.This inoculated plates are incubated for suitable incubation period at optimum temperature.After incubation well isolated colonies are selected.

The nutrient medium used for isolation should contain all required nutrients,source of carbon and nitrogen.Along with this the agar medium should contain a pH indicator dye like neutral red or bromothymol blue and the media should be poorly buffered so that the minor changes in pH of media and production of amine or acid can be detected. After incubation of Inoculated plates the production of acid or amine is detected by the change in colour of media surrounding the colony .The change of colour of media depends on the production of acid or amine.

There is one more method that can be used for screening of organic acid producing micro-organism and that is addition of calcium carbonate in the nutrient media instead of pH indicator dye.The initial method of innoculation is same as above after innoculation the organic acid producing colony shows a clear zone around colony as the organic acid produced by colony dissolves the calcium carbonate present in media.Thus the organic acid producing colonies are further sub-cultured,purified and stock culture is maintained.

c] Screening of organism producing Vitamin,Amino acids and other Growth factors.

Here for screening of organisms a suitable source is selected and serial dilution are made in sterile distill water.This dilution are inoculated on a suitable nutrient agar medium without any vitamin,amino-acid or metabolite .The nutrient media should contain all required essential nutrients except the metabolite or growth factor that is under consideration.The inoculated plates are incubated for a suitable period of time at optimum temperature.After incubation the plates are taken and the colonies obtained may be vitamin,amino-acid or metabolite producer.

The isolated colonies are check for production of metabolites whether the metabolites are produced in excess because the organism producing this metabolites in excess utilize some quantity of metabolites for its growth and excess amount of metabolites are secreted extracellular in vicinity of colony.

2.Secondary Screening

In primary screening we detect and isolated the desired organism but in secondary screening we characterize industrially important micro-organism which are isolated in primary screening by using highly selective procedures.Here in secondary screening we screen the organism that are capable of giving high yield of product by using cheap raw material.

In primary screening only basic information about the isolated colony is obtained and in secondary screening the detail information about the isolate is obtained and it is determined whether the isolate is capable of being used on industrial scale.Before using the isolate on industrial scale determination of its capabilities and yield potential is important so secondary screening plays a very important role.Valueless organism are discarded only valuable organism are used further as secondary screening may involve expensive procedure of screening.The organism suitable for commercial production of product are detected and used further.

Secondary screening is generally  used to obtain information about isolated micro-organism.The information obtained is as follows:-

  1. It can used to determine qualitative as well as quantitative information about strains .Qualitative in the sense determination of inhibitory spectrum in case of antibiotics and yield potential of product and quantitative is determination of quantity of product obtained by using different fermentation media.
  2. Secondary screening helps to determine the product produced by fermentation media by using various techniques like chromatography.
  3. It provide information necessary for classification and identification of organism and due to which the pathogenecity to human and animals can be determined.
  4. Secondary screening helps to determine the genetic instability of strain.It is very important because if organism carry out mutation and loses the capabilities of giving high yield then the industry may face a great loss.
  5. In secondary screening various nutrients that are provided for growth are tested for toxicity so that the any nutrient compound that is toxic to growth of isolated strain should be eliminated .
  6. The chemical solubility of product produce is tested.The organic solvents in which the product can get dissolved are eliminated.
  7. The physical,chemical and biologically properties of product are determined and studied.
  8. The secondary screening determines the capabilities of organism to alter or destroy its own product.

Thus secondary screening is all about collection of broad range of information about the isolated strain and on the bases of this information it is decided whether the selected micro-organism is suitable for use on industrial scale or not.


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Screening of Micro-organism for Industrial Use

Screening of Micro-organism for Industrial Use

The micro-organism that are requiredin industries are screened or we can say isolated from nature.The source from which micro-organism are isolated may be soil,air ,water,compost,milk or food.Isolation of this micro-organism requires specific isolation technique.So search of micro-organism  of our interest from nature can be called as screening.

Screening can defined as”The procedure of isolation,detection and separation of micro-organism from mixed population of our interest by using highly selective procedure is called Screening”.

The main aim of screening is selection of valuable and important micro-organism and removal of valueless micro-organism from microbial population.The procedure used for screening are highly selective and vary from organism to organism like selective media,selective detection system and selective isolation procedure.In screeing an isolated colonies are required except in case of  antibiotic producing micro-organism crowded plate technique is used

In screening of micro-organism their are three important things that are to be considered

  1. Choice of source- A source from which a sample for screening is taken like air,water,soil,food,milk or compost etc.
  2. Choice of substrate- Required nutrients and growth factors should be supplied for the growth of desired micro-organism.
  3. Choice of Detection- A proper isolation and detection of desired micro-organism is important.

In screening of one of the best micro-organism is selected which can give us maximum yield of product.The best isolation procedure, incubation condition and selection techniques are used.

Here one by one we will go through steps that are important and carried out during Screening

  • Suitable source– The samples that are used for isolation of micro-organism should be collected from a suitable source.The samples collected from a particular source should be diluted.
  • Serial Dilution technique– Serial dilution technique is used to dilute collected samples.Reduction in number of micro-organism from original sample is called dillution.If collected sample is solid for example soil then 1 gm of soil is diluted in 10 ml of sterile distill water.As sample is solid 10 ml of water is used as the volume should remain same.If the collected sample is in liquid state foe example milk or water then 1 ml of milk is diluted in 9 ml of sterile distill water.This serial dilution is to be aplied on suitable agar medium by using suitable technique like Streaking technique,Spread plate technique,Pour plate technique.These samples are islolated on agar media and further detected.
  • Incubation– Incubation of isolation plates at suitable temperature for suitable period of time is very important for getting well isolated colonies.
  • Detection system– One of the best indicator and detection system used is pH detection system.A suitable agar media with pH indicator system is used for detection of acid or alkaline producing micro-organisms.
  • Purification – Purification of well isolated colonies is done by re-streaking of isolated colony on suitable agar media.The dilution which gives 25 to 200 colonies on a plate that dilution is used for getting well isolated colonies.The efficency of medium can be incresed by poorly buffering the media.Here in screening we are detecting the acid or alkaine producing micro-organism and not the amount of acid or alkali produce so we can use the media that is poorly buffered.In case if we want high organic acid producing  organism then the media should be strongly buffered.
  • Detection system – In primary detection system we can only detected whether acid or alkaline is produce and if acid is produce it may be organic or inorganic acid.Detection of acid is easy but detrmining the name of acid requires secondary detection system that is the samples are further screened by iolating the samples in liquid media and after incubation the samples are filtered and thin layer chromatography is carried out to determine the specific acid.


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