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Classification of Microbes

Household Applications

  • Lactic acid bacteria (LAB)

    • Milk Curd

    • LAB produces acids that coagulate and partially digest milk proteins.

    • Small amount of curd that is added to the milk for curdling acts as an inoculum containing thousands of LABS, which further multiply.

    • LAB enhances the nutritional value of milk by increasing Vitamin B12.

    • LAB present in stomach prevents infections.

  • Fermentation
    • ​Dosa and idli dough is fermented by bacteria, which produces CO2 gas and gives it a puffed-up appearance.
    • ​Dough used for making breads is fermented by baker’s yeast (Saccharomyces cerevisiae).
    • ​‘Toddy’, a traditional drink from South India is made by fermenting sap from palm trees.
    • The xanthan gum, which is used in thickening of ice creams, puddings, chocolates etc. is obtained by fermentation of starch and molasses. The fermentation is carried out with the help of Xanthomonas sp. Xanthum gum is also used in the production of pigments, fertilizers, weedicides, textile pigments, tooth pastes, high quality paper, etc.

Industrial applications
  • For industrial purposes, microbes are grown in large vessels called fermentors.

  • On industrial scale, fermented beverages, antibiotics, enzymes, and other bioactive molecules are prepared using microbes.

  • Fermented beverages 
    Saccharomyces cerevisiae, also called brewer’s yeast, is used to prepare wine, beer, whisky, brandy, rum, etc. depending upon the type of raw material and processing.

  • If fermented broth is distilled, then brandy and rum are produced while wine and beer are produced without distillation.

  • Antibiotics

    • Certain microorganisms inhibit the growth of other microorganisms wherever they grow.

    • Antibiotics are chemical substances produced by certain microbes that kill or retard the growth of other microbes (disease-causing microbes).

    • Penicillin discovered by Alexander Fleming was the first antibiotic to be discovered.

    • Fleming discovered it by chance when he was working on the bacterium Staphylococcus. He discovered that growth of Staphylococcus ceases in the culture plates where Penicillium notatum was grown.

    • Later on, its use as an effective antibiotic was established by Chain and Florey.

  • Chemicals, enzymes, and bioactive agents


Substance produced

Fungus Aspergillus niger

Citric acid

Bacterium Acetobacter aceti

Acetic acid

Bacterium Clostridium butylicum

Butyric acid

Bacterium Lactobacillus 

Lactic acid

Yeast S.cerevisiae


Bacterium Streptococcus

Streptokinase (used as a clot buster for removing clots from blood vessels of patients with myocardial infarction)

Fungus Trichoderma polysporum

Cyclosporin A (used as immune-suppressive agent in organ transplantation)

Yeast Monascus purpureus

Statins (lower blood cholesterol levels)

  • Leather industry
Bacteria are also used in leather industries during tanning of leather. The soft, perishable parts of the skin (hide) are degraded with the help of certain bacteria.

Do you know which organisms are classified as microorganisms? Let us find out.

  • Microorganisms can be classified into four major groups depending on their characteristics. Let us study the major groups of microorganisms.

There is a lot of variety of microorganisms in nature. The five major groups are as follows:

1. Bacteria

2. Fungi

3. Protozoa

4. Algae

5. Viruses


Bacteria are the most abundant organisms on earth. They are found everywhere − on land, in water, and in the air. They are single-celled microorganisms that have a protective cell wall and lack nucleus. They reproduce by binary fission.


Structure of a Bacterium

Bacteria are classified into three types on the basis of their shape. They predominantly exist in three main shapes:

(i) Rods: They are rod-shaped bacteria and are called bacilli. Examples are E.coli, Salmonella, and Clostridium botulinum.

(ii) Spheres: They are round in shape and are called cocci. An example of cocci is Staphylococci.

(iii) Spirals: They are spiral-shaped and are called spirilli. Examples are Vibrio cholerae and Treponema pallidum.


Fungi are plant-like organisms that are multicellular. They are heterotrophic as they lack chlorophyll. Most of the fungi are invisible to the naked eyes. Yeast and moulds are the examples of fungi that cannot be seen through naked eyes.


We keep the food in the refrigerator for preserving the food for a longer time. However, still have you ever noticed the presence of whitish and greyish patch on the slice of bread? Can you guess what these whitish and greyish patches are?

The white greyish patches are the fungus, a multicellular organism that has developed on the slice of bread. If you observe it under a magnifying glass, then fungus appears as a thread-like structure. These thread-like filaments are called hyphae. They also produce tiny black, rounded structures that are called spores. The sexual and asexual reproduction of fungi takes place via these spores.

Fungi are of three types:

  1. Thread-like fungi − They grow in the form of fine threads and form cottony masses on the surface of things such as bread and cheese. These threads are called hyphae. Some of the hyphae are root-like and grow downwards while some may grow upwards from the surface. The black dots seen on the contaminated bread are actually their spore sacs present at the tip of the hyphae.

  1. Club fungi

A typical example of club fungi is mushroom. A mushroom consists of following parts:

Stalk −Stalk is the upright part of the mushroom.

Cap − It is the umbrella-shaped upper part of the mushroom.

Both of them are made up of hyphae, which are the reproductive parts of the mushroom. Hyphae are tightly packed and are attached to the underground hyphae, which absorb food from the decaying matter. Remember that fungi are saprophytes.

On the underside of the mushroom caps, gills are present that carry spores.

  1. Sac fungi − These fungi are of varying shapes and sizes ranging from unicellular yeast to large morels.


Protozoa are microscopic organisms that include Amoeba, Paramecium, Euglena, Plasmodium, etc. They can be unicellular or multicellular. They are simple primitive organisms that are usually found in water.


Algae are multicellular photosynthetic organisms. Have you ever seen slimy green patches in ponds? What are those green patches called?

The slimy green patches that are seen in ponds are called Spirogyra. Spirogyra is a green filamentous alga, which is commonly found in freshwater habitats. It appears as bright dark green filaments that gently move along with water currents.

Algae are of three types:

  1. Green algae − They contain green pigment called chlorophyll and are capable of performing photosynthesis. They are a major source of food for aquatic organisms. They vary in their shapes and sizes. They can be single-celled such as Chlamydomonas, filamentous such as Spirogyra, or colonial such as Volvox.
    The figure for Chlamydomonas is given below:

  2. Brown algae − Most of them are aquatic and live in water as seaweeds. Examples include Fucus and Laminaria (kelps). Kelps are large and grow up to a length of 60 m. They are rich in minerals such as iodine and calcium and are used to fertilise soil and feed domestic animals. A gummy substance called algin is also obtained from kelps. Algin is used for making ice creams and toothpaste.

  3. Red algae - They are also aquatic and are found in deep sea waters. Most common red alga is Chondrus, which is used for making a jelly-like substance that is used in salad dressing, toothpaste, etc. Aga…

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