Misplaced Pages

#500499

78-471: Besides exploring the multiple layers and parts of the human body within the Medical Database, the prime objective of the game is to destroy all infecting microbes in a hospital patient by use of a fighter ship reduced by shrink ray and inserted into the body. All microbes must be destroyed to accomplish a mission and save the patient. There two kinds of microbes, one that attacks the patient more often and

156-560: A horizontal gene transfer process referred to as natural transformation . Some species form extraordinarily resilient spores , but for bacteria this is a mechanism for survival, not reproduction. Under optimal conditions bacteria can grow extremely rapidly and their numbers can double as quickly as every 20 minutes. Most living things that are visible to the naked eye in their adult form are eukaryotes , including humans . However, many eukaryotes are also microorganisms. Unlike bacteria and archaea , eukaryotes contain organelles such as

234-413: A few extremely rare exceptions, such as Thiomargarita namibiensis . Bacteria function and reproduce as individual cells, but they can often aggregate in multicellular colonies . Some species such as myxobacteria can aggregate into complex swarming structures, operating as multicellular groups as part of their life cycle , or form clusters in bacterial colonies such as E.coli . Their genome

312-454: A healthy animal, and cause illness. Based on these experiments, he devised criteria for establishing a causal link between a microorganism and a disease and these are now known as Koch's postulates . Although these postulates cannot be applied in all cases, they do retain historical importance to the development of scientific thought and are still being used today. The discovery of microorganisms such as Euglena that did not fit into either

390-407: A higher survival than when irradiated with gamma rays, for a same irradiation dose); The physiological state of individuals (e.g., the tardigrade species Richtersius coronifer and Milnesium tardigradum are more resistant to gamma-ray radiation when in the hydrated state, and Macrobiotus areolatus is more resistant to X-ray radiation when in the anhydrobiotic state). The way lethality is measured

468-494: A host they are known as pathogens and then they are sometimes referred to as microbes . Microorganisms play critical roles in Earth's biogeochemical cycles as they are responsible for decomposition and nitrogen fixation . Bacteria use regulatory networks that allow them to adapt to almost every environmental niche on earth. A network of interactions among diverse types of molecules including DNA, RNA, proteins and metabolites,

546-470: A large dose (7.0 Gy ) during the Goiânia accident , and lived, whereas his wife, who got a dose of 5.7 Gy, died. The most likely explanation is that his dose was fractionated into many smaller doses which were absorbed over a length of time while his wife stayed in the house more and was subjected to continuous irradiation without a break so giving the self repair mechanisms in her body less time to repair some of

624-502: A large group of photosynthetic eukaryotes that include many microscopic organisms. Although some green algae are classified as protists , others such as charophyta are classified with embryophyte plants, which are the most familiar group of land plants. Algae can grow as single cells, or in long chains of cells. The green algae include unicellular and colonial flagellates , usually but not always with two flagella per cell, as well as various colonial, coccoid , and filamentous forms. In

702-435: A large industrial scale by microbial fermentation include acetic acid produced by acetic acid bacteria such as Acetobacter aceti , butyric acid made by the bacterium Clostridium butyricum , lactic acid made by Lactobacillus and other lactic acid bacteria , and citric acid produced by the mould fungus Aspergillus niger . Microorganisms are used to prepare bioactive molecules such as Streptokinase from

780-520: A membrane as in a eukaryote, and the presence of endosymbionts. This is seen to be the first plausible evolutionary form of microorganism, showing a stage of development from the prokaryote to the eukaryote. Archaea are prokaryotic unicellular organisms, and form the first domain of life in Carl Woese 's three-domain system . A prokaryote is defined as having no cell nucleus or other membrane bound - organelle . Archaea share this defining feature with

858-431: A mutualistic symbiosis between the two. However, these signals can be eavesdropped by other microorganisms, such as the soil bacteria , Myxococcus xanthus , which preys on other bacteria. Eavesdropping, or the interception of signals from unintended receivers, such as plants and microorganisms, can lead to large-scale, evolutionary consequences. For example, signaler-receiver pairs, like plant-microorganism pairs, may lose

SECTION 10

#1733084940501

936-416: A narrow region known as the rhizosphere that supports many microorganisms known as the root microbiome . These microorganisms in the root microbiome are able to interact with each other and surrounding plants through signals and cues. For example, mycorrhizal fungi are able to communicate with the root systems of many plants through chemical signals between both the plant and fungi . This results in

1014-590: A pH of 2.0 or less. Piezophiles thrive at very high pressures : up to 1,000–2,000 atm , down to 0 atm as in a vacuum of space . A few extremophiles such as Deinococcus radiodurans are radioresistant , resisting radiation exposure of up to 5k Gy . Extremophiles are significant in different ways. They extend terrestrial life into much of the Earth's hydrosphere , crust and atmosphere , their specific evolutionary adaptation mechanisms to their extreme environment can be exploited in biotechnology , and their very existence under such extreme conditions increases

1092-496: A relatively fast rate of evolution. Most microorganisms can reproduce rapidly, and bacteria are also able to freely exchange genes through conjugation , transformation and transduction , even between widely divergent species. 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 . This rapid evolution

1170-437: A remnant genome. Like bacteria, plant cells have cell walls , and contain organelles such as chloroplasts in addition to the organelles in other eukaryotes. Chloroplasts produce energy from light by photosynthesis , and were also originally symbiotic bacteria . Unicellular eukaryotes consist of a single cell throughout their life cycle. This qualification is significant since most multicellular eukaryotes consist of

1248-478: A single cell called a zygote only at the beginning of their life cycles. Microbial eukaryotes can be either haploid or diploid , and some organisms have multiple cell nuclei . Unicellular eukaryotes usually reproduce asexually by mitosis under favorable conditions. However, under stressful conditions such as nutrient limitations and other conditions associated with DNA damage, they tend to reproduce sexually by meiosis and syngamy . Of eukaryotic groups,

1326-601: A solution for pollution. In the Middle Ages , as an early example of biological warfare , diseased corpses were thrown into castles during sieges using catapults or other siege engines . Individuals near the corpses were exposed to the pathogen and were likely to spread that pathogen to others. In modern times, bioterrorism has included the 1984 Rajneeshee bioterror attack and the 1993 release of anthrax by Aum Shinrikyo in Tokyo. Radioresistance Radioresistance

1404-482: 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. Further evolution was slow, and for about 3 billion years in the Precambrian eon , (much of the history of life on Earth ), all organisms were microorganisms. Bacteria, algae and fungi have been identified in amber that

1482-471: A vital organ . For many short term radiation deaths (3 days to 30 days) the loss of cells forming blood cells ( bone marrow ) and the cells in the digestive system (wall of the intestines ) cause death. There is strong evidence that radioresistance can be genetically determined and inherited, at least in some organisms. Heinrich Nöthel, a geneticist from the Freie Universität Berlin carried out

1560-573: A well-oxygenated filter bed such as a slow sand filter . Anaerobic digestion by methanogens generate useful methane gas as a by-product. Microorganisms are used in fermentation to produce ethanol , and in biogas reactors to produce methane . Scientists are researching the use of algae to produce liquid fuels , and bacteria to convert various forms of agricultural and urban waste into usable fuels . Microorganisms are used to produce many commercial and industrial chemicals, enzymes and other bioactive molecules. Organic acids produced on

1638-977: A wide range of chemicals and enzymes. They are invaluable in research as model organisms . They have been weaponised and sometimes used in warfare and bioterrorism . They are vital to agriculture through their roles in maintaining soil fertility and in decomposing organic matter. They also have applications in aquaculture, such as in biofloc technology . Microorganisms are used in a fermentation process to make yoghurt , cheese , curd , kefir , ayran , xynogala , and other types of food. Fermentation cultures provide flavour and aroma, and inhibit undesirable organisms. They are used to leaven bread , and to convert sugars to alcohol in wine and beer . Microorganisms are used in brewing , wine making , baking , pickling and other food -making processes. These depend for their ability to clean up water contaminated with organic material on microorganisms that can respire dissolved substances. Respiration may be aerobic, with

SECTION 20

#1733084940501

1716-420: Is 200 R , but about 4 hours later it is of 7,000 R (for X-ray intensity of 110 R/minute), and haploid (= male) embryos are more resistant than diploid (= female) embryos. The mortality of adults H. hebetor exposed to a dose of 180,250 R is the same to this of a non-irradiated control group (food was not provided to either groups) (for 6,000 R/minute). However, a lower dose of 102,000 R (for 6,000 R/minute)

1794-596: Is 220 million years old, which shows that the morphology of microorganisms has changed little since at least the Triassic period. 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 . Microorganisms tend to have

1872-577: Is a stub . You can help Misplaced Pages by expanding it . This scientific software article is a stub . You can help Misplaced Pages by expanding it . Microbes A microorganism , or microbe , is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells . The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from sixth century BC India. The scientific study of microorganisms began with their observation under

1950-476: Is also a term sometimes used in medicine ( oncology ) for cancer cells which are difficult to treat with radiotherapy . Radioresistance of cancer cells may be intrinsic or induced by the radiation therapy itself. The comparison in the table below is only meant to give approximate indications of radioresistance for different species and should be taken with great caution. There are generally big differences in radioresistance for one species among experiments, due to

2028-404: Is also source of variation for the estimated radioresistance of a species. Irradiated specimens are not instantly killed, unless exposed to a very high dose (acute dose). Therefore, irradiated specimens die over a certain period of time and lower irradiation doses correspond to longer survival. This means that the radiation dose LD 50 fluctuates with the time at which it is measured. For example,

2106-438: Is considered to be one of the fathers of microbiology . He was the first in 1673 to discover and conduct scientific experiments with microorganisms, using simple single-lensed microscopes of his own design. Robert Hooke , a contemporary of Leeuwenhoek, also used microscopy to observe microbial life in the form of the fruiting bodies of moulds . In his 1665 book Micrographia , he made drawings of studies, and he coined

2184-507: Is high in oceans, deep sea-vents, river sediment and an acidic river, suggesting that many eukaryotic microbial communities may yet be discovered. The fungi have several unicellular species, such as baker's yeast ( Saccharomyces cerevisiae ) and fission yeast ( Schizosaccharomyces pombe ). 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. The green algae are

2262-414: Is important in medicine, as it has led to the development of multidrug resistant pathogenic bacteria , superbugs , that are resistant to antibiotics . A possible transitional form of microorganism between a prokaryote and a eukaryote was discovered in 2012 by Japanese scientists. Parakaryon myojinensis is a unique microorganism larger than a typical prokaryote, but with nuclear material enclosed in

2340-463: Is incorrect to assume that diseases appear one by one in humans. Disease infects by spreading from one person to another. This infection occurs through seeds that are so small they cannot be seen but are alive. In 1546 , Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact, or even without contact over long distances. Antonie van Leeuwenhoek

2418-402: Is sufficient to induce a state of lethargy in H. hebetor that is manifested by a complete cessation of activity, including cessation of feeding, and these individuals eventually let themselves starve to death. And an even lower dose of 4,858 R (for 2,650 R/minute) is sufficient to sterilize adult female H. hebetor (sterility arises 3 days post-exposure). Other important factors that influence

Bodyworks Voyager: Missions in Anatomy - Misplaced Pages Continue

2496-437: Is the level of ionizing radiation that organisms are able to withstand. Ionizing-radiation-resistant organisms (IRRO) were defined as organisms for which the dose of acute ionizing radiation (IR) required to achieve 90% reduction (D10) is greater than 1,000 gray (Gy) Radioresistance is surprisingly high in many organisms, in contrast to previously held views. For example, the study of environment, animals and plants around

2574-504: Is usually a circular bacterial chromosome – a single loop of DNA , although they can also harbor small pieces of DNA called plasmids . These plasmids can be transferred between cells through bacterial conjugation . Bacteria have an enclosing cell wall , which provides strength and rigidity to their cells. They reproduce by binary fission or sometimes by budding , but do not undergo meiotic sexual reproduction . However, many bacterial species can transfer DNA between individual cells by

2652-948: Is utilised by the bacteria to achieve regulation of gene expression . In bacteria, the principal function of regulatory networks is to control the response to environmental changes, for example nutritional status and environmental stress. A complex organization of networks permits the microorganism to coordinate and integrate multiple environmental signals. Extremophiles are microorganisms that have adapted so that they can survive and even thrive in extreme environments that are normally fatal to most life-forms. Thermophiles and hyperthermophiles thrive in high temperatures . Psychrophiles thrive in extremely low temperatures. – Temperatures as high as 130 °C (266 °F), as low as −17 °C (1 °F) Halophiles such as Halobacterium salinarum (an archaean) thrive in high salt conditions , up to saturation. Alkaliphiles thrive in an alkaline pH of about 8.5–11. Acidophiles can thrive in

2730-516: The Charales , which are the algae most closely related to higher plants, cells differentiate into several distinct tissues within the organism. There are about 6000 species of green algae. Microorganisms are found in almost every habitat present in nature, including hostile environments such as the North and South poles , deserts , geysers , and rocks . They also include all the marine microorganisms of

2808-510: The Chernobyl disaster area has revealed an unexpected survival of many species, despite the high radiation levels. A Brazilian study in a hill in the state of Minas Gerais which has high natural radiation levels from uranium deposits, has also shown many radioresistant insects , worms and plants. Certain extremophiles , such as the bacteria Deinococcus radiodurans and the tardigrades , can withstand large doses of ionizing radiation on

2886-554: The animal or plant kingdoms, since they were photosynthetic like plants, but motile like animals, led to the naming of a third kingdom in the 1860s. In 1860 John Hogg called this the Protoctista , and in 1866 Ernst Haeckel named it the Protista . 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. It

2964-508: The cell nucleus , the Golgi apparatus and mitochondria in their cells . The nucleus is an organelle that houses the DNA that makes up a cell's genome. DNA (Deoxyribonucleic acid) itself is arranged in complex chromosomes . Mitochondria are organelles vital in metabolism as they are the site of the citric acid cycle and oxidative phosphorylation . They evolved from symbiotic bacteria and retain

3042-475: The human body , microorganisms make up the human microbiota , including the essential gut flora . The pathogens responsible for many infectious diseases are microbes and, as such, are the target of hygiene measures . The possible existence of microscopic organisms was discussed for many centuries before their discovery in the seventeenth century. By the 6th century BC , the Jains of present-day India postulated

3120-456: The microscope in the 1670s by Anton van Leeuwenhoek . In the 1850s, Louis Pasteur found that microorganisms caused food spoilage , debunking the theory of spontaneous generation . In the 1880s, Robert Koch discovered that microorganisms caused the diseases tuberculosis , cholera , diphtheria , and anthrax . Because microorganisms include most unicellular organisms from all three domains of life , they can be extremely diverse. Two of

3198-400: The oceans and deep sea . Some types of microorganisms have adapted to extreme environments and sustained colonies; these organisms are known as extremophiles . Extremophiles have been isolated from rocks as much as 7 kilometres below the Earth's surface, and it has been suggested that the amount of organisms living below the Earth's surface is comparable with the amount of life on or above

Bodyworks Voyager: Missions in Anatomy - Misplaced Pages Continue

3276-456: The poles to the equator , in deserts , geysers , rocks , and the deep sea . Some are adapted to extremes such as very hot or very cold conditions , others to high pressure , and a few, such as Deinococcus radiodurans , to high radiation environments. Microorganisms also make up the microbiota found in and on all multicellular organisms . There is evidence that 3.45-billion-year-old Australian rocks once contained microorganisms,

3354-432: The protists are most commonly unicellular and microscopic. This is a highly diverse group of organisms that are not easy to classify. Several algae species are multicellular protists, and slime molds have unique life cycles that involve switching between unicellular, colonial, and multicellular forms. The number of species of protists is unknown since only a small proportion has been identified. Protist diversity

3432-496: The ability to communicate with neighboring populations because of variability in eavesdroppers. 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. A lichen is a symbiosis of a macroscopic fungus with photosynthetic microbial algae or cyanobacteria . Microorganisms are useful in producing foods, treating waste water, creating biofuels and

3510-676: The bacteria with which they were once grouped. In 1990 the microbiologist Woese proposed the three-domain system that divided living things into bacteria, archaea and eukaryotes, and thereby split the prokaryote domain. Archaea differ from bacteria in both their genetics and biochemistry. For example, while bacterial cell membranes are made from phosphoglycerides with ester bonds, Achaean membranes are made of ether lipids . Archaea were originally described as extremophiles living in extreme environments , such as hot springs , but have since been found in all types of habitats . Only now are scientists beginning to realize how common archaea are in

3588-759: The bacterium Streptococcus , Cyclosporin A from the ascomycete fungus Tolypocladium inflatum , and statins produced by the yeast Monascus purpureus . Microorganisms are essential tools in biotechnology , biochemistry , genetics , and molecular biology . 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. They are particularly valuable in genetics , genomics and proteomics . Microorganisms can be harnessed for uses such as creating steroids and treating skin diseases. Scientists are also considering using microorganisms for living fuel cells , and as

3666-408: The blood of cattle that were infected with anthrax always had large numbers of Bacillus anthracis . Koch found that he could transmit anthrax from one animal to another by taking a small sample of blood from the infected animal and injecting it into a healthy one, and this caused the healthy animal to become sick. He also found that he could grow the bacteria in a nutrient broth, then inject it into

3744-476: The broths at the beginning of his experiment. Nothing grew in the broths in the course of Pasteur's experiment. This meant that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. Thus, Pasteur refuted the theory of spontaneous generation and supported the germ theory of disease . In 1876, Robert Koch (1843–1910) established that microorganisms can cause disease. He found that

3822-406: The damage done by the radiation. This resulted in her death. He also eventually died in 1994. In the same way some of the persons who worked in the basement of the wrecked Chernobyl have built up doses of 10 Gy, these workers received these doses in small fractions so the acute effects were avoided. It has been found in radiation biology experiments that if a group of cells are irradiated then as

3900-827: The desiccation-adaptation hypothesis proposes that the extreme temperatures present in the habitats of hyperthermophiles like Deinococcus radiodurans cause cellular damage that is virtually identical to damage typically caused by ionizing radiation, and that the cellular repair mechanisms that have evolved to repair this heat or desiccation damage are generalizable to radiation damage as well, allowing D. radiodurans to survive extreme doses of ionizing radiation. Exposure to gamma radiation leads to cellular DNA damage including alterations in nitrogenous base-pairing, sugar-phosphate backbone damage, and double-stranded DNA lesions. The extraordinarily efficient cellular repair mechanisms that Deinococcus species like D. radiodurans have evolved to repair heat-damage are likely also capable of reversing

3978-404: The dose increases the number of cells which survive decrease. It has also been found that if a population of cells are given a dose before being set aside (without being irradiated) for a length of time before being irradiated again then the radiation has less of an ability to cause cell death . The human body contains many types of cells and a human can be killed by the loss of a single tissue in

SECTION 50

#1733084940501

4056-418: The earliest direct evidence of life on Earth. 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 . Microbes are essential tools in biology as model organisms and have been put to use in biological warfare and bioterrorism . Microbes are a vital component of fertile soil . In

4134-509: The effects of DNA damage wrought by ionizing radiation, such as by piecing back together any components of their genome that have been fragmented by the radiation. Bacillus sp. producing unusually radiation (and peroxide) resistant spores, have been isolated from spacecraft assembly facilities, and are thought of as candidates that could ride piggyback on spacecraft through interplanetary transfer. Genome analysis of some of these radiation resistant spore producers have thrown some light on

4212-426: The environment, with Thermoproteota (formerly Crenarchaeota) being the most common form of life in the ocean, dominating ecosystems below 150 metres (490 ft) in depth. These organisms are also common in soil and play a vital role in ammonia oxidation. 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

4290-512: The existence of microorganisms as discovered by modern science. 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 first-century BC book entitled On Agriculture in which he called the unseen creatures animalia minuta, and warns against locating a homestead near a swamp: … and because there are bred certain minute creatures that cannot be seen by

4368-434: The existence of tiny organisms called nigodas . 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. According to Mahavira , the 24th preacher of Jainism, the humans destroy these nigodas on a massive scale, when they eat, breathe, sit, and move. Many modern Jains assert that Mahavira's teachings presage

4446-440: The eyes, which float in the air and enter the body through the mouth and nose and they cause serious diseases. In The Canon of Medicine (1020), Avicenna suggested that tuberculosis and other diseases might be contagious. 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

4524-523: The game as being an "entertaining and educational" title with "decent graphics and an average interface". Nick Smith of Allgame described Bodyworks Voyager as "easy to pick up, fun and educational", although becoming "somewhat repetitive after a few hours". Comparing the game to Microcosm Martin Klimes of PC Review found Bodyworks Voyager to lack the graphics and quality of a commercial standalone game. This educational video game -related article

4602-541: The genetic traits that could be responsible for the resistances observed. In general, radioresistance in prokaryotes is achieved by two cellular mechanisms. The first is protection of the proteome and DNA from ionizing radiation induced damage. The second is recruitment of highly sophisticated DNA repair mechanisms that enable the reconstruction of a fully functional genome . These DNA repair mechanisms include homologous recombinational repair, and extended synthesis-dependent strand annealing . Radioresistance

4680-476: The latter that attacks the ship more often. In the ship's control system there are four utilities. The target indicator determines where shots are fired. The patient screen indicates the patient's vitality and the microbe threat level presence. The radar show's the ship's and microbes' positions. The ship screen indicates the ship's vitality and firepower rate. Bodyworks Voyager received mixed reviews upon release. Steve Greenlee of Computer Game Review described

4758-469: The level of radioresistance include: The length of time during which a dose of radiation is delivered—with doses delivered during longer periods, or at time intervals, being associated with greatly reduced negative effects; The feeding state of individuals—with pre-fed and post-fed individuals being more resistant to radiations compared to starved individuals; The type of radiation used (e.g., tardigrades Milnesium tardigradum irradiated with heavy ions have

SECTION 60

#1733084940501

4836-430: The levels of some cytoplasmic and nuclear proteins and increased gene expression , DNA repair and other processes. Also biophysical models presented general basics for this phenomenon. Many organisms have been found to possess a self-repair mechanism that can be activated by exposure to radiation in some cases. Two examples of this self-repair process in humans are described below. Devair Alves Ferreira received

4914-453: The most extensive study about radioresistance mutations using the common fruit fly , Drosophila melanogaster , in a series of 14 publications. From the perspective of evolutionary history and causation, radioresistance does not appear to be an adaptive trait because there is no documented naturally occurring selection pressure that could have bestowed a fitness advantage to the ability for organisms to withstand doses of ionizing radiation in

4992-498: The most immediate impact on microbiology by allowing for the cultivation of a wide range of microbes with wildly different physiologies. Winogradsky was the first to develop the concept of chemolithotrophy and to thereby reveal the essential role played by microorganisms in geochemical processes. He was responsible for the first isolation and description of both nitrifying and nitrogen-fixing bacteria . French-Canadian microbiologist Felix d'Herelle co-discovered bacteriophages and

5070-640: The order of 5,000 Gy . In the graph on left, a dose/survival curve for a hypothetical group of cells has been drawn with and without a rest time for the cells to recover. Other than the recovery time partway through the irradiation, the cells would have been treated identically. Radioresistance may be induced by exposure to small doses of ionizing radiation. Several studies have documented this effect in yeast , bacteria , protozoa , algae , plants, insects, as well as in in vitro mammalian and human cells and in animal models . Several cellular radioprotection mechanisms may be involved, such as alterations in

5148-409: The potential for extraterrestrial life . The nitrogen cycle in soils depends on the fixation of atmospheric nitrogen . This is achieved by a number of diazotrophs . 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 . The roots of plants create

5226-511: The range that several extremophile species have been observed to be capable of surviving. This is primarily because the Earth's magnetic field shields all its inhabitants from solar cosmic radiation and galactic cosmic rays, which are the two primary sources of ionizing radiation across our solar system, and even including all documented terrestrial sources of ionizing radiation such as radon gas and primordial radionuclides at geographical locations considered to be natural high-level radiation sites,

5304-447: The same amount of time post-exposure also poses some challenges of interpretation. These examples illustrate the many issues associated with comparison of radioresistance among species and the need for caution when doing so. ∗ While an LD 50 has been reported for wild type C. elegans individuals, an upper lethal limit has not been established, rather "nearly all animals were alive with no indication of excess lethality up to 800 Gy,

5382-550: The size of organism, gives an estimate of perhaps 1 trillion species on the planet, of which most would be microorganisms. Currently, only one-thousandth of one percent of that total have been described. Archael cells of some species aggregate and transfer DNA from one cell to another through direct contact, particularly under stressful environmental conditions that cause DNA damage . Like archaea, bacteria are prokaryotic – unicellular, and having no cell nucleus or other membrane-bound organelle. Bacteria are microscopic, with

5460-442: The surface. Extremophiles have been known to survive for a prolonged time in a vacuum , and can be highly resistant to radiation , which may even allow them to survive in space. 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

5538-488: 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 . The number of prokaryotes is estimated to be around five nonillion, or 5 × 10 , accounting for at least half the biomass on Earth. The biodiversity of the prokaryotes is unknown, but may be very large. A May 2016 estimate, based on laws of scaling from known numbers of species against

5616-423: The term cell . Louis Pasteur (1822–1895) exposed boiled broths to the air, in vessels that contained a filter to prevent particles from passing through to the growth medium , and also in vessels without a filter, but with air allowed in via a curved tube so dust particles would settle and not come in contact with the broth. By boiling the broth beforehand, Pasteur ensured that no microorganisms survived within

5694-526: The three domains, Archaea and Bacteria , only contain microorganisms. The third domain, Eukaryota , includes all multicellular organisms as well as many unicellular protists and protozoans that are microbes. Some protists are related to animals and some to green plants . Many multicellular organisms are also microscopic, namely micro-animals , some fungi , and some algae , but these are generally not considered microorganisms. Microorganisms can have very different habitats , and live everywhere from

5772-480: The way radiation affects living tissues and to different experimental conditions. We should for example consider that because radiation impedes cell division, immature organisms are less resistant to radiations than adults, and adults are sterilized at doses much lower than that necessary to kill them. For example, for the insect parasitoid Habrobracon hebetor , the LD 50 for haploid embryo during cleavage (1–3 hours of age)

5850-484: The yearly dose of natural background radiation remains tens of thousands of times smaller than the levels of ionizing radiation that many highly radioresistant organisms can withstand. One possible explanation for the existence of radioresistance is that it is an example of co-opted adaptation or exaptation, where radioresistance could be an indirect consequence of the evolution of a different, linked adaptation that has been positively selected for by evolution. For example,

5928-459: The β radiation dose that causes 50% mortality in the American cockroach at 25 days post-exposure is 5,700 R, but to reach 50% mortality at 3 days post-exposure, 45,610 R are needed. 25 days can represent a long survival period for short lived species, such as insects, but would represent a very short survival time for long lived species, such as mammals, so comparing survival of different species after

6006-444: Was not until the work of Martinus Beijerinck and Sergei Winogradsky late in the nineteenth century that the true breadth of microbiology was revealed. Beijerinck made two major contributions to microbiology: the discovery of viruses and the development of enrichment culture techniques. While his work on the tobacco mosaic virus established the basic principles of virology, it was his development of enrichment culturing that had

6084-410: Was one of the earliest applied microbiologists. 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

#500499