There are 4 major types of microorganisms: protozoa, bacteria, algae, and fungi. The virus is the 5th type of microorganism, but it cannot survive independently like the other 4 types. They can only live inside the body of a host, either a human or animal). All these microorganisms have different shapes and structures; some of them are single-celled(protozoa), and the others are multicellular. Microorganisms can be both helpful and harmful to humans in the following ways:

• Friendly microorganisms: Microorganisms that are useful to humans for various purposes are considered friendly microorganisms. For example, bacteria present naturally in the human digestive system help in digesting food. The behaviour of microbes interacting with each other and their surroundings can help scientific research and development in virology, biotechnology, microbiology, and immunology.
• Harmful microorganisms: Microorganisms that are damaging to humans are considered harmful microorganisms. For example, disease-causing viruses are harmful microorganisms.

How to prevent the growth of microbes in food

• Microorganisms that grow in our food cause them to rot or spoil by releasing toxic substances that cause food poisoning. Salts and oils can be used to counter the growth of microorganisms. They are called preservatives.
• There is another way to prevent the growth of microbes in food. Extreme temperatures kill microbes, which is why the process of refrigeration and pasteurisation can keep the food free from harmful microbes. Pasteurisation is the process of boiling milk to 70℃ for 15 to 30 seconds and then suddenly cooling and storing it. This process was discovered by Louis Pasteur, which is why it is called ‘pasteurisation’.
• Keeping fruits and vegetables fresh means preventing them from microbial action. This can be done by sealing it in an airtight container.

Where are microorganisms found?

Microorganisms can survive in all kinds of environments, such as ice, water, land, etc. They can also live inside the bodies of animals and humans. Some microorganisms need other organisms to survive, while others can live independently. Algae are found on land and water surfaces. They are abundant in marshy areas. Viruses cannot survive without a host. Such types of microorganisms are also called parasites.

Microorganisms are useful to humans in the following ways:

• Fermentation:
  • Lactobacillus, a kind of bacteria, is used to make curd from milk.
  • Bacteria are also used to make cheese and ferment rice for dishes like dosa, idlis, etc.
  • Yeast, a type of fungus, is used in the process of making bread, pastries, and cakes.
  • Yeast is also used to make alcohol and wine by converting natural sugars and food grains like barley, wheat, rice, crushed fruit juices, etc. into alcohols.
  • Fun Fact: Fermentation was discovered by Louis Pasteur in 1857.
• Medicine: Some microorganisms can stop the growth of other disease-causing microorganisms; they are used in the production of medicines called antibiotics. The two types of microorganisms used in the production of antibiotics are bacteria and fungi. Streptomycin, tetracycline, and erythromycin are examples of antibiotics derived from bacteria. Antibiotics can also cure microbial infections in animals and are used as pesticides to prevent diseases in plants.
  
  • Fun Fact: Vaccines consist of disease-causing microbes that enter the body and enable the body to produce natural antibodies. These microbes are often dead or weakened. Vaccines can prevent major diseases like polio, hepatitis B, and smallpox.
  • Fun Fact: Alexander Fleming discovered penicillin, and Edward Jenner discovered the vaccine for smallpox in 1798.
• Soil fertility: Some microorganisms, such as bacteria, are natural nitrogen fixers. Nitrogen is essential for soil fertility. The soil needs a certain ratio of nitrogen, potassium, and phosphorus to grow a healthy yield. Microorganisms decompose organic matter and increase the nitrogen in the soil along with other nutrients.
  
  
• Decomposition: Microorganisms decompose dead and decaying matter in the soil. It acts as a natural cleanser after the life cycle of a plant or animal ends. They decompose organic waste and man-made garbage as long as they are biodegradable. Biodegradable waste is waste that can be decomposed by microorganisms naturally. This way, they clean the environment and enrich the soil at the same time. The decomposed matter is called compost, and it acts as manure and nourishes the soil.

• Humans: Microorganisms can be harmful to humans by causing diseases. Different types of microorganisms have different methods of transmitting diseases through the air, water, or food. Sometimes, they can even spread by contact or touch. These microorganisms are known as pathogens. A pathogen may enter our body through the water we drink or the food we eat. They may also enter through the air we breathe or when we touch a person carrying the pathogen in their bodies. The diseases that spread from one person to another are called communicable diseases. If we come into contact with the carrier animal or insect, then we can contract the disease. Disease-causing microbes act as carriers when they sit on the garbage and organic waste. They carry pathogens from here to the food we eat when they sit on it. That is why it is advisable to always keep your food covered and free from insects.

  • Note: The female Aedes mosquito is the carrier of the dengue virus, and the female Anopheles mosquito carries the malaria pathogen. These mosquitos breed in stagnant water, such as that present in open drains, water coolers, flower pots, etc. By preventing collection of stagnant water in our surroundings, we can prevent mosquitoes from breeding near us.

Some common communicable diseases and the microorganisms that cause them are:

1. Tuberculosis: Bacteria(through the air)
2. Measles: Virus(through the air)
3. Chicken Pox: Virus(through air or contact)
4. Polio: Virus(through air or water)
5. Cholera: Bacteria(through water or food)
6. Typhoid: Bacteria(through the air)
7. Hepatitis A: Virus(through water)
8. Malaria: Protozoa(through a mosquito bite)
9. Dengue: Virus(through a mosquito bite)

• Plants: Some common plant diseases caused by microorganisms are:

1. Citrus Canker: Bacteria(through the air)
2. Rust of Wheat: Fungi(through air or seeds)
3. Yellow vein mosaic of okra: Virus(through insects)

• Animals: Some common animal diseases caused by microorganisms are:

1. Anthrax: Bacterium
2. Foot and Mouth Disease of cattle: Virus
   
   

Preventive measures: Some general measures to keep in mind with people suffering from communicable diseases are:

• Keep the patient in complete isolation.
• Maintain personal hygiene around the patient.
• Drink boiled water.
• Consult a doctor for available vaccinations for the disease.
• Use mosquito nets and repellents.
• Spray insecticides and control mosquito breeding by preventing the collection of stagnant water.
• Consume easy-to-digest food that is freshly cooked and not stale.
• Sanitise hands and surrounding areas repeatedly.

Plants need nitrogen to function but they cannot use it directly from the atmosphere or the soil. They need the help of certain bacteria and other microbes present in the soil to fix the atmospheric nitrogen by converting them into nitrogen compounds, the form in which plants can absorb nitrogen. You already know about a bacterium, known as Rhizobium, present in the roots of leguminous plants. It fixes atmospheric oxygen so that the roots of plants can absorb it.

There are millions of microorganisms present in our environment. We can categorise them as useful and harmful for human beings. Microorganisms are used in various human activities from fermentation to medical purposes. We must also be aware of the dangers of harmful microorganisms and the diseases they cause in human beings. It is important to understand the role played by microorganisms in the world around us. To learn more about microorganisms, join MSVgo by downloading the app for free! Learn science interactively and be an MSVgo champ!