Differential Radio-resistance in Nutrition Induced Morphotypes of Deinococcus radiodurans R1

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Cobalt (58Co/60Co) has various applications in many industries and processes such as alloy production for orthopedic applications, cold pasteurization agent in food industry, petrochemical industries, gas turbine generation process and radiotherapy.1-3 Besides, it is also one of the byproducts of nuclear and defense related industries. During operation of nuclear power plants, many γ- emitting activated corrosion products are generated which contain various radionuclide’s such as 51Cr, 59Fe, 58Co, 65Zn, 54Mn and 60Co.4 Among which, 60Co is the most significant radioactive element due to its longer half-life (5.26 years) and emission of higher (1.17 and 1.33 MeV) gamma energies.5 During the decontamination process in the nuclear industry, a mixture of ion chelating agents and organic acids like Ethylenediaminetetraacetic acid (EDTA), Nitrilotriacetic acid, citric acid and ascorbic acid are added that generates citrate, oxalate and EDTA complexes of cobalt. Among which cobalt citrate and cobalt oxalate can easily be removed by chemical precipitation in post-decontamination processes but the removal of cobalt-EDTA complex, i.e. [Co(III)-EDTA]– is cumbersome due to its high stability and solubility.6 Chelated form of cobalt such as [Co(III)-EDTA]– is more soluble and mobile than that of non-chelated form.7 Apart from chelation, oxidation states of the cobalt also determine the solubility and mobility of cobalt. Oxidation state of cobalt in EDTA complex play a major role and determine the stability and mobility of cobalt near waste disposal sites. Oxidized form of cobalt, Co(III) has a stronger affinity to EDTA than that of the Co(II), that is why [Co(III)-EDTA]– has higher stability and solubility.8 Since, most transportable form of 6...

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...t are expected to have higher radiotolarance.26 These habitats might act as rich repositories for the isolation of novel microorganisms with potential bioremediation applications for radioactive nuclear waste.26 In this present study, a [Co(III)-EDTA]- reducing bacterium Bacillus licheniformis SPB2 was isolated from a solar salt pan and reduction conditions for [Co(III)-EDTA]- were optimized. We report the reduction of [Co(III)-EDTA]- to [Co(II)-EDTA]2- by B. licheniformis SPB2 at much higher concentration (i.e. 1 mM) than the reported value in post-decontamination nuclear waste processing (0.01 mM). Various aspects of [Co(III)-EDTA]- reduction were also studied. B. licheniformis SPB2 also showed substantial radio-tolerance. This report concludes that novel microbial isolates from the naturally stressed environment are useful for bioremediation of hazardous waste.

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