Radiation resistant bacteria

Experiments were carried out which showed that the ratio of TT/UT (4 8) observed in the acid hydrolysate of a DNA was nearly the same as the ratio (5 2) found in the products of the more gentle enzymatic hydrolysis. Other experiments showed that the photoreactivating enzyme could excise all three dimers equally readily, that all three dimers were implicated in the photoinactivation of primer DNA, and that CT dimers were excised from the DNA of radiation-resistant bacteria. 

The reports on radiation-resistant organisms on other sea foods include codfish (8), flounder, rockfish, and salmon (5), and haddock and clams (10). Liuzzo and co-workers (7) studied the morphology and metabolism of seven radiation-resistant bacteria isolated from fresh Gulf shrimp to ascertain if radiation altered their characteristics. They observed radiation-induced differences in optimum incubation temperature, chromogenesis, carbohydrate and vitamin utilization, and action on litmus milk (Tables V and VI). 

Daly MJ (2000) Engineering radiation-resistant bacteria for environmental biotechnology. Curr Opin Biotechnol 11 280—285. 

DNA synthesis in irradiated sensitive bacterial cells is permanently inhibited by doses which produce about 5 thymine dimers per single strand of DNA (1000 p.). In the cells of resistant bacteria, DNA synthesis is inhibited only by doses of radiation which produce about 500 dimers per cell. The difference between the two types of bacteria is caused by the presence in the resistant cells of efficient enzymatic mechanisms for repairing the damage done by thymine dimerization. 

The bacterial counts show extreme variations in irradiated fish or shellfish irradiated at 0.2-0.3 Mrad after 14-21 days storage at 33°F. These variations can range from no bacteria from one sample irradiated at 0.2 to 0.3 Mrad to millions of bacteria per gram on another sample irradiated at the same levels of radiation. To control these variations, it will ultimately be necessary to understand some of the factors that contribute to radiation resistance. 

Lewis, C.K. and Burt Maxcy, R. (1984) Effect of physiological age on radiation resistance of some bacteria that are highly radiation resistant. Appl. Environ. Microbiol. 47, 915-918. 

Other Properties. Polyester fibers have good resistance to uv radiation although prolonged exposure weakens the fibers (47,51). PET is not affected by iasects or microorganisms and can be designed to kill bacteria by the iacorporation of antimicrobial agents (19). The oleophilic surface of PET fibers attracts and holds oils. Other PET fiber properties can be found ia the Hterature (47,49). 

Irradiation. Although no irradiation systems for pasteurization have been approved by the U.S. Food and Dmg Administration, milk can be pasteurized or sterilized by P tays produced by an electron accelerator or y-rays produced by cobalt-60. Bacteria and enzymes in milk are more resistant to irradiation than higher life forms. For pasteurization, 5000—7500 Gy (500,000—750,000 tad) are requited, and for inactivating enzymes at least 20,000 Gy (2,000,000 rad). Much lower radiation, about 70 Gy (7000 tad), causes an off-flavor. A combination of heat treatment and irradiation may prove to be the most acceptable approach. 

Spore Formation Some bacteria form spores when growth ceases due to starvation or other causes. Spores are more resistant than normal cells to heat, drying, radiation, and chemicals. Spores can remain alive for many years however, they can convert back to normal cells at proper conditions. Spore-forming bacteria are found most commonly in the soil. 

The BSE agent is smaller than most viral particles and is highly resistant to heat, ultraviolet light, ionizing radiation, and common disinfectants that normally render viruses and bacteria inactive. It causes no detectable immune or inflammatory response in the host, and has not been observed microscopically. 

In bacteria, mutation is an important mechanism by which resistance to antibiotics and other antimicrobial chemicals is achieved, although the receipt of entirely new genes directly from other bacteria is also clinically very important. Spontaneous mutation rates (rates not influenced by mutagenic chemicals or ionizing radiation) vary substantially depending on the gene and the organism in question, but rates of 10-5-10-7 are typical. These values... 

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