Microorganism

A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. They have been suspected to exist since ancient times, with early mentions in Jain literature from 6th-century BC India. The scientific study of these tiny creatures began in the 1670s when Anton van Leeuwenhoek first observed them using a microscope. Later discoveries by scientists like Louis Pasteur and Robert Koch showed that microorganisms cause things like food spoilage and diseases such as tuberculosis, cholera, diphtheria, and anthrax.

Microorganisms are incredibly diverse and make up most unicellular organisms in all three domains of life. Two of these domains, Archaea and Bacteria, consist only of microorganisms. The third domain, Eukaryota, includes many unicellular creatures like protists and protozoans, as well as all multicellular organisms. These tiny life forms can live almost anywhere—from the poles to the equator, in deserts, geysers, rocks, and the deep sea. Some can even survive in extreme conditions such as very high heat, cold, pressure, or radiation.

Microbes play many important roles in our world. They help ferment foods, treat sewage, and produce useful substances like fuel, enzymes, and other bioactive compounds. They are also essential for healthy soil and are found all around and inside us as part of the human microbiota, including the important gut flora. While some microbes can cause infectious diseases, many are beneficial and necessary for life on Earth.

Discovery

See also: History of biology and Microbiology § History

The idea that tiny, unseen organisms might exist was talked about for many years before they were actually discovered. 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 and lived for only a fraction of a second.

The real science of studying these tiny creatures began in the 1670s when Anton van Leeuwenhoek used a simple microscope to look at drops of water and other things. 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 and drew what he saw. 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 anywhere on Earth. Bacteria and archaea are almost always microscopic, while a number of eukaryotes are also microscopic, including most protists, some fungi, as well as some micro-animals and plants. Viruses are generally regarded as not living and therefore not considered to be microorganisms, although a subfield of microbiology is virology, the study of viruses.

Single-celled microorganisms were the first forms of life to develop on Earth, approximately 3.5 billion years ago. Microorganisms tend to evolve quickly because they can reproduce rapidly and exchange genetic material easily. This quick evolution helps them survive in new environments and adapt to changes. A unique microorganism discovered in 2012 shows features between simple and more complex cells, offering clues about how life might have developed on Earth.

Ecology

Main article: Microbial ecology

Microorganisms live almost everywhere in nature, including places that seem very harsh, like the North and South poles, deserts, and even deep under the ground. Some special kinds of these tiny living things, called extremophiles, can survive in very hot, cold, salty, or high-pressure places where most other life could not. These extremophiles can even live in space or deep inside the Earth.

Microorganisms also have important jobs for our planet. They help break down dead plants and animals and play a big role in making sure nutrients like nitrogen are 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. Even though some tiny creatures have been used in harmful ways in history, 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. For example, 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.

However, some microorganisms can make us sick. These are called pathogens and can cause diseases like plague, tuberculosis, malaria, and ringworm. 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 novel The War of the Worlds, alien lifeforms try to take over Earth but are stopped by a common microbe that humans are immune to.

The 2001 film Osmosis Jones and its show Ozzy & Drix take place inside a stylized human body and feature anthropomorphic microorganisms. In the 2006 indie game FlOw, players control an aquatic microorganism that grows by absorbing others.