Investigation of radiation resistant bacteria from irradiation cell pool water of Type IV gamma irradiator

Radiation processing plant, Vashi, Navi Mumbai, India is one of the type IV, wet storage type irradiator with maximum design capacity of 1 MCi ⁶⁰Co source activity. An attempt was made to isolate and study radiation resistant bacteria from irradiation cell pool water of the facility. Number of water samples were collected from the irradiation cell pool water and investigated for the resistant organisms. An average of 550 CFU of microorganisms per liter of the pool water sample was observed. Few experiments were carried out by precipitating the pool water organisms on 0.45 μ cellulose nitrate membrane by filtration technique and exposing these membranes on soyabean case in digest agar to gamma radiation dose of 3, 4 and 5 kGy in gamma chamber GC-4000. The membranes were incubated at 30-35 °C for 2-3 days and it is observed that 3.3% and 0.58% of the organisms showed survival at radiation doses of 3 and 4 kGy respectively with no survival at 5 kGy radiation dose. More than 25 such bacterial isolates were studied in detail. The microscopic observation reveals that most of the isolated organisms were gram positive rods some of them arranged in long chains resembling Actino bacteria. The radiation sensitivity studies showed that two of the isolates were having D₁₀ values of more than 4 kGy, one of the isolate showing D₁₀ value as high as 4.7 kGy which is 50 times more than that of E. coli, a common gut bacterium. All the bacterial isolate studied showed variations in the biochemical test indicating diverse group of organisms. Being highly radiation resistant, these bacteria may be exploited for bioremediation of nuclear and radioactive waste. (author)