Microorganism
The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from sixth century BC India.
[further explanation needed] Microorganisms can have very different habitats, and live everywhere from the poles to the equator, in deserts, geysers, rocks, and the deep sea.
[1][2] Microbes are important in human culture and health in many ways, serving to ferment foods and treat sewage, and to produce fuel, enzymes, and other bioactive compounds.
[3] These nigodas are said to be born in clusters; they live everywhere, including the bodies of plants, animals, and people; and their life lasts only for a fraction of a second.
[5] The earliest known idea to indicate the possibility of diseases spreading by yet unseen organisms was that of the Roman scholar Marcus Terentius Varro in a 1st century BC book entitled On Agriculture in which he called the unseen creatures animalia minuta, and warns against locating a homestead near a swamp:[6] … and because there are bred certain minute creatures that cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and they cause serious diseases.
[7][8] Turkish scientist Akshamsaddin mentioned the microbe in his work Maddat ul-Hayat (The Material of Life) about two centuries prior to Antonie van Leeuwenhoek's discovery through experimentation: It is a mistake to assume that diseases appear in individuals one by one.
[12][13][14][15] Robert Hooke, a contemporary of Leeuwenhoek, also used microscopy to observe microbial life in the form of the fruiting bodies of moulds.
[20][21][22] The work of Pasteur and Koch did not accurately reflect the true diversity of the microbial world because of their exclusive focus on microorganisms having direct medical relevance.
[24] While his work on the tobacco mosaic virus established the basic principles of virology, it was his development of enrichment culturing that had the most immediate impact on microbiology by allowing for the cultivation of a wide range of microbes with wildly different physiologies.
[34][35] Bacteria, algae and fungi have been identified in amber that is 220 million years old, which shows that the morphology of microorganisms has changed little since at least the Triassic period.
[36] The newly discovered biological role played by nickel, however – especially that brought about by volcanic eruptions from the Siberian Traps – may have accelerated the evolution of methanogens towards the end of the Permian–Triassic extinction event.
Most microorganisms can reproduce rapidly, and bacteria are also able to freely exchange genes through conjugation, transformation and transduction, even between widely divergent species.
[38] This horizontal gene transfer, coupled with a high mutation rate and other means of transformation, allows microorganisms to swiftly evolve (via natural selection) to survive in new environments and respond to environmental stresses.
Parakaryon myojinensis is a unique microorganism larger than a typical prokaryote, but with nuclear material enclosed in a membrane as in a eukaryote, and the presence of endosymbionts.
In 1990 the microbiologist Woese proposed the three-domain system that divided living things into bacteria, archaea and eukaryotes,[42] and thereby split the prokaryote domain.
[47] The combined domains of archaea and bacteria make up the most diverse and abundant group of organisms on Earth and inhabit practically all environments where the temperature is below +140 °C (284 °F).
They are found in water, soil, air, as the microbiome of an organism, hot springs and even deep beneath the Earth's crust in rocks.
[54] Some species such as myxobacteria can aggregate into complex swarming structures, operating as multicellular groups as part of their life cycle,[55] or form clusters in bacterial colonies such as E.coli.
This qualification is significant since most multicellular eukaryotes consist of a single cell called a zygote only at the beginning of their life cycles.
Some fungi, such as the pathogenic yeast Candida albicans, can undergo phenotypic switching and grow as single cells in some environments, and filamentous hyphae in others.
[68] Microorganisms are found in almost every habitat present in nature, including hostile environments such as the North and South poles, deserts, geysers, and rocks.
[72][73] A network of interactions among diverse types of molecules including DNA, RNA, proteins and metabolites, is utilised by the bacteria to achieve regulation of gene expression.
One way this can occur is in the root nodules of legumes that contain symbiotic bacteria of the genera Rhizobium, Mesorhizobium, Sinorhizobium, Bradyrhizobium, and Azorhizobium.
In adapting to avoid local eavesdroppers, signal divergence could occur and thus, lead to the isolation of plants and microorganisms from the inability to communicate with other populations.
[86][87] Microorganisms are useful in producing foods, treating waste water, creating biofuels and a wide range of chemicals and enzymes.
Microorganisms are used in a fermentation process to make yoghurt, cheese, curd, kefir, ayran, xynogala, and other types of food.
[96] Microorganisms are used to prepare bioactive molecules such as Streptokinase from the bacterium Streptococcus,[97] Cyclosporin A from the ascomycete fungus Tolypocladium inflatum,[98] and statins produced by the yeast Monascus purpureus.
The yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe are important model organisms in science, since they are simple eukaryotes that can be grown rapidly in large numbers and are easily manipulated.
However, other diseases such as influenza, yellow fever or AIDS are caused by pathogenic viruses, which are not usually classified as living organisms and are not, therefore, microorganisms by the strict definition.
In food preparation, microorganisms are reduced by preservation methods such as cooking, cleanliness of utensils, short storage periods, or by low temperatures.
