Microorganisms as Foes and Friends: There are millions of organisms on Earth, and one way or the other, each one of them has a role to play in the ever-changing ecosystem. While a few make their presence felt prominently, others get the job done silently and hushed. But the role of each one of them is important to sustain life on Earth, in both positive and negative aspects. One of these types of organisms is the single-celled ones, called Microorganisms.

You might have observed a green patch in wet areas, bread that gets spoilt when kept for long, milk turning into curd overnight etc. All these are the tasks performed by these microbes or microorganisms that cannot be seen through the naked eye. In this article, we shall study the different types of microorganisms and how they help and destroy things in various ways.

Types of Microorganisms

Microorganisms are classified into four major groups:

• Bacteria
• Fungi
• Protozoa
• Algae

These microorganisms or microbes are so small in size that they cannot be seen with the unaided eye. Some of these, such as the fungus that grows on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope. That is why these are called microorganisms or microbes.

Viruses are also microscopic but are different from other microorganisms. However, they reproduce only inside the host organism’s cells, which may be a bacterium, plant or animal. Viruses cause common ailments like cold, influenza (flu) and most coughs. Viruses also cause serious diseases like polio and chicken pox. Diseases like dysentery and malaria are caused by protozoa(protozoans), whereas typhoid and tuberculosis (TB) are bacterial diseases.

Role of Microorganisms in Human Life

Microorganisms as foes and friends play an important role in our lives. Some of them are beneficial in many ways whereas some others are harmful and cause diseases. Let us study about them in detail.

Friendly Microorganisms

Microorganisms are used for various purposes. They are used in the preparation of curd, bread and cake. They are also used in cleaning up the environment. For example, the organic wastes (vegetable peels, animal remains, feces, etc.) are broken down into harmless and usable substances by bacteria. Recall that bacteria are also used in the preparation of medicines. In agriculture, they are used to increase soil fertility by fixing nitrogen.

Making of Curd and Bread

Curd contains several microorganisms. Of these, the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd. Bacteria are also involved in the making of cheese,
pickles and many other food items. An important ingredient of rava (sooji), idlis and bhaturas is curd. Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.

Commercial Use of Microorganisms

Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar). Yeast is used for commercial production of alcohol and wine. For this purpose yeast is grown on natural sugars
present in grains like barley, wheat, rice, crushed fruit juices, etc.

Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the
dough and increase its volume. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes. Sugar can be converted into alcohol by yeast. This process of conversion of sugar into alcohol is known as fermentation.

Medicinal Use of Microorganisms

Whenever you fall ill, the doctor may give you some antibiotic tablets, capsules or injections such as of
penicillin. The source of these medicines is microorganisms. These medicines kill or stop the growth of the
disease-causing microorganisms. Such medicines are called antibiotics. These days a number of antibiotics are being produced from bacteria and fungi. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Antibiotics are even mixed with the feed of livestock and poultry to check microbial infection in animals. They are
also used to control many plant diseases.

A few other uses of friendly microorganisms are:

• Vaccine Preparation
• Increasing Soil Fertility
• Cleaning the Environment

Harmful Microorganisms

As we have discussed before, different types of microorganisms as foes and friends help us in many ways, and also cause harm in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing and leather. Let us study more about their harmful activities.

Disease Causing Microorganisms in Humans

Pathogens enter our body through the air we breathe, the water we drink or the food we eat. They can also get transmitted by direct contact with an infected person or carried by an animal. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.

Disease Causing Microorganisms in Animals

Several microorganisms not only cause diseases in humans and plants, but also in other animals. For example, anthrax is a dangerous human and cattle disease caused by a bacterium. Foot and mouth disease of cattle is caused by a virus.

Disease Causing Microorganisms in Plants

Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops. They can be controlled by the use of certain chemicals which kill the microbes.

Food Poisoning

Food poisoning could be due to the consumption of food spoilt by some microorganisms. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. So, it is very important that we preserve food to prevent it from being spoilt.

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