A microorganism or microbe is an organism that is microscopic (too small to be visible to the naked eye). Microorganisms are often described as single-celled, or unicellular organisms; however, some unicellular protists are visible to the naked eye, and some multicellular species are microscopic. The study of microorganisms is called microbiology.
Microorganisms can be found almost anywhere in the taxonomic organization of life on the planet. Unicellular organisms carry out all the functions of life. Bacteria and archaea are almost always microscopic, whilst a number of eukaryotes are also microscopic, including most protists and a number of fungi. Unicellular species are those whose members consist of a single cell throughout their life cycle. This qualification is significant since most multicellular organisms consist of a single cell at the beginning of their life cycles. Unicellular organisms usually contain only a single copy of their genome when not undergoing cell division, although some organisms have multiple cell nuclei.
Microorganisms are found in virtually every habitat present in nature. Even in hostile environments such as the poles, deserts, geysers, rocks, and the deep sea, some types of microorganisms have adapted to the extreme conditions and sustained colonies; these organisms are known as extremophiles. Some extremophiles have been known to survive for a prolonged time in a vacuum, and some are unusually resistant to radiation. Many types of microorganisms have intimate symbiotic relationships with other larger organisms; some of which are mutually beneficial (mutualism), while others can be damaging to the host organism (parasitism). If microorganisms can cause disease in a host they are known as pathogens.
Microorganisms are used in brewing, baking and other food-making processes. They are also essential tools in biotechnology and the study of biochemistry, genetics and molecular biology. They can also be harmful as a significant cause of human disease, and some have uses as biological weapons. Microorganisms have an important place in all ecosystems and in most higher-order multicellular organisms (as symbionts). They are vital to the environment, as they participate in the Earth's element cycles (such as the carbon cycle and nitrogen cycle). They are also involved in the recycling of other organisms' dead remains and waste products. Read more ...
These May Be the Deepest Traces of Life on Earth National Geographic - April 10, 2017
A hidden ecosystem seems to lurk six miles below the Mariana Trench, offering clues for finding life across the solar system. On Earth circa four billion years ago, life was hard. Frequent asteroid strikes turned parts of the planet into molten rock. Food and livable spaces were few and far between. What was a microbe to do to survive?
Did Microbes Shape the Human Life Span? Live Science - December 24, 2014
The microbes that live in and on humans may have evolved to preferentially take down the elderly in the population, a new computer model suggests. That, in turn, could have allowed children a greater share of food and resources, thereby enabling an extended childhood. Such a microbial bias may also have kept the first human populations more stable and resilient to upheavals, the findings suggest.
Microbes to be 'last survivors' on future Earth BBC - July 2, 2013
The last surviving creatures on Earth will be tiny organisms living deep underground, according to scientists. Researchers used a computer model to assess our planet's fate billions of years from now. They found that as the Sun becomes hotter and brighter, only microbes would be able cope with the extreme conditions that the solar changes would bring.
Super microbe's life code cracked BBC - January 10, 2005
Experts have deciphered the complete DNA sequence for one of the most infectious germs known to science. The Francisella tularensis bacterium is a candidate bioterror weapon, as it takes just 10 microbes to bring on disease in humans. The genome sequencing work is already speeding up the search for a vaccine against the potentially deadly bug.
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