هما خراسانی اسماعیلی

In the last decade, biology and microorganisms is built to clean up environmental pollutants such as heavy metals. Isolation of metal resistant strains to achieve the goal is very important and the aim of this study was isolate the chrome resistant strains. Five samples of oil contaminated soils of Khuzestan zones were collected under sterile conditions and transferred to laboratory immediately. The soil samples were homogenized and diluted by sterile saline up to 10-10 and cultured on Luria Bertani agar containing 5ppm potassium dichromate. Resistant strains were isolated after 24 hours of incubation, and then for isolation of appropriate strains, cultured on Macconkey agar. Isolated bacteria were identified by biochemical tests. Then, Luria Bertani agar was used for screening of resistant strains in form of MIC test. The best conditions for bacterial growth were found in the presence of chromium in various temperatures, rate of shaking and pH values by spectrophotometry at 600 nm in the overnight of cultivation. Absorption tests of metal were started under optimal conditions. From total of 24 strains of isolated Pseudomonads, 14 strains were resistant to chromium. The best strain (Mac-2) had removed 35.60 % of chromium from aqueous culture mediums under optimal conditions (pH: 8, Temp: 40°C and Shaking rate: 200rpm).Discussion and Since heavy metals in various physicochemical forms are considered as environmental pollutants in most parts of the world, thus, the contaminated regions must be detoxified. The isolated strain can be used for studies of bioremediation of chromium contaminated sites.