Radiations are energy in the form of waves or particles. They are of two forms, ionizing radiations and non-ionizing radiations. Ionizing radiations are radiations of short wavelength and high energy which causes atoms to ionize. Examples of ionizing radiations includes: x-rays, gamma rays, ultra violet radiation. Non-ionizing radiations are radiations of long wavelengths and low energy. Examples of non ionizing radiations includes infra-red rays and visible lights e.t.c Effects of ionizing radiations on organisms are extreme which includes: mutations, breakage of hydrogen bonds, oxidation of double bonds, polymerization of some molecules, generation of radicals like singlet oxygen and OH radicals, formation of thymine dimmers, breakage of tryptophan into toxic photoproducts .the most lethal effect of ultra violet radiation is that its wavelengths can be absorbed by the DNA (deoxyribonucleic acid) of most microbial cells. These effects are dangerous to a cell and nearly all cells do not survive exposures to radiation but a particular organism we are considering radioresistant organisms a group of extremophiles survive these condition and not only survive these conditions but also thrive. Examples of these organisms include:
Extreme ionizing-radiation resistance has been observed in several members of the domains; Bacteria and Achaea. Of the genera containing ionizing-radiation resistant organisms, Deinococcus and Rubrobacter show the highest levels of resistance, and all species of these genera have been shown to be either gamma radiation resistant or UV radiation resistant or both. Microorganisms of the genus Deinococcus, which Include D. radiodurans is the type species of this genus, and the best studied member. All known members of the genus are radioresistant: D. proteolyticus, D. radiopugnans, D. radiophilus, D. grandis, D. indicus, D. frigens, D. saxicola, D. marmoris, D. deserti,D. geothermalis and D. murrayi; the latter two are also thermophilic.Other ionizing-radiation resistant bacteria have been isolated and described; these include some species of the genera; Acinetobacter, Chroococcidiopsis, Hymenobact er, Kineococcus, Kocuria, and Methylobacterium ,Hyperthermophilic euryarchaeote species of the genera Thermococcus and Pyrococcus also contain ionizing-radiation-resistant strains . Species of the genera Deinococcus and Rubrobacter have been shown to survive exposure to doses greater than 25 kGy, while species of the genus Chroococcidiopsis survive exposure to 15 kGy . Strains of the species Acinetobacter radioresistens, Hymenobacter actinosclerus, Kineococcus radiotolerans, Methylobacterium radiotolerans, Pyrococcus furiosus, Pyrococcus abyssi, Thermococcus gammatolerans, Thermococcus marinus, and Thermococcus radiotolerans are less resistant and have been shown to survive after exposure to much lower levels of radiation. Where kGy means gray (Gy). A unit of absorbed radiation equal to 1 joule of energy absorbed by 1 kg of material. (1 Gy = 100 RAD; 103Gy =1 kGy.) HABITAT OF THESE MICROORGANISMS
Data on natural habitats, of radioresistant bacteria are not numerous. In a number of cases it is difficult to distinguish their natural habitats, as they were isolated from the samples which were previously exposed to X-ray or gamma-irradiation, or from the ecosystems with the naturally raised radioactivity but Habitats of these organisms can include sterilized containers ,ground meat ,feces, air , fresh water, sewage, vacuum, sawdust ,sewage ,paper mill machinery ,animal feeds ,processed meat ,dried food ,feather pillows , room dust ,textiles ,irradiated meat and fish ,high-level nuclear waste sites ,thermally polluted water ,and irradiated rice. Other environments from which radiation-resistant isolates have been obtained include; soil feaces, warm freshwater geothermal springs and shallow and abyssal marine thermal springs, even clinical sources. They are found widely and in various habitats...
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