What Are Microbes?

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Micro-organisms (or microbes for short) play a very important role in our lives. Some microbes cause disease but the majority are completely harmless. In fact we couldn’t live without them, but they could live without us.

These microscopic organisms play a key role in maintaining life on earth, fixing gases and breaking down dead plant and animal matter into simpler substances that are used at the beginning of the food chain. Biotechnologists can also exploit the activities of microbes to benefit humans, such as in the production of medicines, enzymes and food. They are also used to breakdown sewage and other toxic wastes into safe matter. This process is called bioremediation.

Microbes are very small living organisms, so small that most of them are invisible. The majority can only be seen with a microscope, which magnifies their image so we can see them. In fact microbes are so tiny you would find over a million in a teaspoon of soil. They make up more than 60 % of the Earth’s living matter and scientists estimate that 2-3 billion species share the planet with us.


Microbes – bacteria, archaea, fungi, algae, protozoa and viruses – have been around for at least 3,500 million years and were the only life forms on Earth for most of that time. As the Earth cooled, liquid water formed and the first microbial life appeared. The conditions on Earth in the beginning were very hostile so the first microbes probably resembled the archaea, as they were able to live in the extreme environments such as the high temperature found on the cooling planet.

Around 2,800 million years ago, cyanobacteria, the largest and most diverse group of photosynthetic bacteria, probably appeared. This was an important development as these were the first organisms able to carry out aerobic photosynthesis. It is thought that cyanobacteria were responsible for raising the level of oxygen in the Earth’s atmosphere from less than 1 % to the 21 % of today. The presence of oxygen in the atmosphere allowed the evolution of new aerobic (oxygen using) species of microbes, which began to colonize every habitat on the planet.

Different species of cyanobacteria formed complex microbial communities with other types of microbes as they evolved, and these communities have left an extensive fossil record. They are fossilized in structures called stromatolites, dome-shaped mounds formed by the merger of mineral sediments into microbial mats.

Mammals and flowering plants are relative newcomers and only appeared around 100 million years ago.

Microbes affect every aspect of life on earth. They have an amazing variety of shapes and sizes and can exist in a wide range of habitats from hot springs to the icy wastes of Antarctica and inside the bodies of animals and plants.

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Read more at Microbiology Society . . . . .

Read also:

Microbes: Our tiny, crucial allies . . . . .