CONTROL OF MICROORGANISMS BY PHYSICAL METHOD..

2) RADIATION:  
       Radiation is the energy transmitted through the space in the varieties of forms. Major types of radiations includes ionizing radiation; UV radiation, Ultrasonication.

i) Ionizing Radiation: It has high energy & can ionize the atoms. They have energy above 10eV. On such radiation pass via cells they create unstable ions & free radicals(H- radicals, OH-radicals, & some peroxides). This radical causes different types intracellular damage whereas ions combines & destroys proteins & nucleic acids causing death. Some of the common ionizing radiation are Gamma rays, X-rays, alpha & beta particles.

  

  • X-rays: They are electromagnetic waves with wavelength smaller than 10nm. X-rays are lethal to mos & higher organisms. However, they are impracticable  for controlling mos because they are expensive to produce, difficult to handle efficiently & since radiations are given off in all directions from the point of origin .However, X-rays are important in producing microbial mutants. (http://en.wikipedia.org/wiki/Mutagenesis)  
  • Gamma rays: They have wavelength of 10^-3  to 10^-2 nm . It is high energy yielding radiation emitted from certain radioactive isotope of Cobalt .Gamma rays are similar to x-rays but of shorter wavelength & high energy. Gamma rays are used in commercial sterilization of materials with high thickness & volume like package of food & medical devices. 
ii) UV Radiation:  It has wavelength between 100 to 400 nm with wavelength 265 nm  is most destructive to bacteria. When mos is subjected to UV light cellular DNA absorbs the energy & form Thymine molecules linked together( thymine dimer) or pyridine dimer. This thymine dimer molecules impairs protein synthesis & replication leading mutation. UV rays are used to reduce microbial population in hospital operating rooms, in aseptic filling rooms, pharmaceutical  industries, food & diary industries & for treatment of contaminated foods.( http://www.rcsb.org/pdb/101/motm.do?momID=91)


iii) Other Radiation:  Ultrasonication( Ultrasonic Vibration) :  They are high frequency sound waves beyond the range of human ears. It is important in fluids as it causes the formation of microscopic bubbles or cavities. Later this cavities collapse & sends out shock waves which ultimately disintegrates the mos in fluid due to external pressure. Though it has few practical application a device called "Sonicator" or "Cavitron"  is used by Dentist to clean teeth. This technique is widely used in research purposes like isolation of sub-cellular structure like antigen, enzymes, toxins,& organelles. It is most effective when used  with an  effective germicide. The above figure shows a Sonicator used by Dentist.  


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