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A cluster of Escherichia coli bacteria magnified 10,000 times.

Microorganisms, often referred to as microbes, encompass a wide range of tiny life forms too small to be seen by the naked eye. The scientific field dedicated to their study is known as Microbiology. Microorganisms encompass several types of life forms including bacteria, fungi, archaea, protists, and viruses.

Classification and Characteristics

Microorganisms are a diverse group that includes several distinct types of life forms. They include bacteria, fungi, archaea, protists, and viruses. Viruses, while not technically classified as living organisms, are often included in discussions of microbiology due to their significant effects on living organisms.

Most microorganisms are unicellular, but some multicellular organisms are also microscopic. Many microorganisms, including most bacteria and archaea, are single-celled organisms. There are also some multicellular microbes, such as certain species of fungi and algae.

Habitat and Ecology

Microorganisms are found in nearly every environment on Earth. They can live in extreme conditions such as hot springs on the ocean floor or deep within the Earth's crust, where extremophiles thrive. Their ability to adapt to such diverse environments underscores their crucial role in the planet's ecosystems.

Microorganisms are integral to nutrient recycling in ecosystems as they serve as decomposers, breaking down dead organic material and returning nutrients to the soil. Some microorganisms also participate in the nitrogen cycle, converting atmospheric nitrogen into a form that plants can use.

Types of Microorganisms

Free-living Microorganisms

Free-living microorganisms obtain energy through various means. Some utilize photosynthesis, while others decompose organic material in their environment. Microorganisms are responsible for the decay of organic material, a vital process for nutrient cycling in ecosystems. In addition, many foods humans consume, like bread, cheese, yogurt, beer, and wine, are processed with the aid of microbes.

Parasitic Microorganisms

Some microorganisms, often referred to as pathogens, can invade host organisms and cause diseases. Examples of diseases caused by viruses include chickenpox, mumps, and measles. Bacterial infections can result in diseases such as tuberculosis and tetanus. Proper hygiene practices, including proper food handling, handwashing, and avoiding close contact with ill individuals, can prevent many microbial infections.

Commensal Microorganisms

Commensalism involves a relationship between two organisms where one benefits without harming the other. Many microorganisms live in or on host organisms without causing harm. Some, like the gut flora in humans, are essential for digestion and overall health.

See Also


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Contributors: Prab R. Tumpati, MD