Microorganism

A microorganism, or microbe, is a very tiny living thing. It can be single-celled or a group of cells called a colony. People have thought about these tiny creatures for a long time. Early writings in Jain literature from long ago talked about them. Scientists started studying them in the 1600s when Anton van Leeuwenhoek saw them with a microscope. Later, scientists like Louis Pasteur and Robert Koch learned that microbes can make food go bad and cause sickness.

Microorganisms are very different from each other and make up most unicellular organisms in all three domains of life. Two of these domains, Archaea and Bacteria, only have tiny organisms. The third domain, Eukaryota, has many tiny creatures like protists and protozoans, as well as bigger plants and animals. These small life forms can live almost everywhere—from the poles to the equator, in deserts, geysers, rocks, and the deep sea. Some can even live in very tough places with extreme heat, cold, pressure, or radiation.

Microbes do many important things for our world. They help ferment foods, treat sewage, and make useful things like fuel, enzymes, and other bioactive compounds. They are also important for healthy soil and live all around and inside us as part of the human microbiota, including the gut flora. While some microbes can make us sick, many are helpful and very important for life on Earth.

Discovery

See also: History of biology and Microbiology § History

People have thought about tiny, unseen organisms for a very long time. As early as the 6th century BC, the Jains in India talked about tiny living things called nigodas. They believed these tiny beings were everywhere.

The real science of studying these tiny creatures began in the 1670s. A man named Anton van Leeuwenhoek used a simple microscope to look at drops of water. He was the first person to see and describe microorganisms, which he called "animalcules." Around the same time, Robert Hooke also used microscopes to look at things like mould. He even came up with the word "cell" to describe the small boxes he saw in plant tissue.

Classification and structure

Microorganisms can be found almost everywhere on Earth. Bacteria and archaea are almost always tiny, while many eukaryotes are also tiny. This includes most protists, some fungi, and some micro-animals and plants. Viruses are usually not considered living things, so they are not counted as microorganisms. But there is a field of science called microbiology that studies viruses, called virology.

Tiny, single-celled microorganisms were the first forms of life on Earth, appearing about 3.5 billion years ago. They change quickly because they can reproduce fast and share their genetic material easily. This helps them live in new places and adapt to changes. In 2012, scientists found a special microorganism that shows features of both simple and more complex cells, giving us hints about how life may have started on Earth.

Ecology

Main article: Microbial ecology

Microorganisms live almost everywhere, even in very tough places like the North and South poles, deserts, and deep underground. Some special kinds, called extremophiles, can survive in very hot, cold, salty, or high-pressure places where most other life could not. These tiny living things have important jobs for our planet. They help break down dead plants and animals and play a big role in making nutrients like nitrogen available for other living things. Some tiny creatures live close to plants and help them grow, while others can make plants sick.

Applications

Main article: Human interactions with microbes

Microorganisms are very useful in many ways. They help us make food like yoghurt, cheese, bread, and beer. They are also important for cleaning water and making energy from things like plants and waste. In science, tiny creatures like yeast are used to study genes and cells.

Microbes are important for farming too. They help plants grow by giving them nutrients and protecting them from sickness. Most of them are very helpful to us.

Human health

Main articles: Pathogen and Germ theory of disease

Further information: Medical microbiology and Parasite

Microorganisms can live inside our bodies and help us stay healthy. The tiny organisms in our gut, called gut flora, help protect our immune system and make important vitamins like folic acid and biotin. Some of these helpful microbes are called probiotics and can be found in dietary supplements or food additives.

Some microorganisms can make us sick. These are called pathogens and can cause diseases. Keeping things clean helps prevent these harmful germs from causing illness. Good hygiene practices, like washing hands and cooking food properly, keep us safe from infections.

In fiction

In H. G. Wells’s 1898 science fiction book The War of the Worlds, alien lifeforms try to take over Earth but are stopped by a tiny germ that humans are safe from.

The 2001 film Osmosis Jones and its show Ozzy & Drix happen inside a human body and show anthropomorphic tiny living things. In the 2006 game FlOw, players control a water germ that grows by taking in others.