| As one of the essential materials, chromium (Cr) and chromium salt are widely used in many industries, such as electroplating, dyeing and printing, metallurgy, chemistry, tanning, mining, papermaking , mechanical industry, and so on , which may produce large amount of waste water and waste residue containing chromium polluting environment. chromium is toxic, mutagenic, and carcinogenic, witch could enter our body through skin and digestive tract. So, it is urgent and necessary for us to find and employ some effective ways to deal with waste water and waste residue containing chromium. In natural environment, chromium mainly has two states, tervalent state [Cr(Ⅲ)] and hexavalent state [Cr(Ⅵ)]. Cr(Ⅵ) is more toxic than Cr(Ⅲ), witch is about 100 times of Cr(Ⅲ), and besides Cr(Ⅲ) is much less soluble than Cr(Ⅵ), witch makes Cr(Ⅲ) easy to be get rid from water. so, converting Cr(Ⅵ) to Cr(Ⅲ) is an efficient detoxification way and the key procedure to eliminate Cr from water. Up to now, most countries adopt chemical methods to detoxify Cr(Ⅵ) , which the cost is very high because large amount of reducing agent needs to be used. Furthermore, such procedures may lead to secondary contamination. So, the use of microorgansms to eliminate Cr(Ⅵ) is becoming the highlight focus of Cr(Ⅵ) contamination management, which has low cost, small energy consumption and free of secondary contamination.In this research, the aim is to isolate some highly efficient detoxification strains from environment, to deal with Cr(Ⅵ) contaminated exhausted water with low cost, good feasibility and good effect. One strain was isolated from the Cr(Ⅵ) seriously contaminated environment with high resistance and good detoxification ability to Cr(Ⅵ), which was identified as Alcaligenes sp.. And some elementary researches about its property and mechanism of Cr(Ⅵ) elimination were conducted. Some of the conclusions are just as the following:1.After one month of consecutive taming, purification and isolation, one strain called as CQMU-1 with high Cr(Ⅵ) resistance and Cr(Ⅵ) detoxification was found from sediments collected at exhausted water drainage outlet of the electroplating factory. In LB liquid culture medium, its resistance to Cr(Ⅵ) was up to 500mg/L and after 72h of shake cultivation at 30℃, at the concentration of 200mg/L Cr(Ⅵ) , 66% of Cr(Ⅵ) could be eliminated.2.Through the morphology, standard physiology, biochemistry detection and 16S rDNA sequence homological analysis, CQMU-1 was identified as Alcaligenes sp.. It is gram negative, sphere or short rod in shape, 1.66μm～1.96μm×0.9μm～1.05μm in body size and 1～3 flagellae around its body. Cultured 48 hours on LB plate, the colony is 0.05～0.15 cm in diameter, low, with round shape, smooth and moist surface, neat periphery, red color and the condition of pH7.0～8.0 , 20～35℃is most suitable for its survival. Besides, CQMU-1 is chemoheterotrophs, aerobic. It does not have fermentation process, does not decompose cellulose, does not hydrolyze gelatin, oxidase and katalase positive, litmus milk alkali positive, anaerobic nitrate aerogenesis positive and can survive in liquid culture witch ammonia is the only nitrogen source. It's nutrition spectrum is wide, can utilize most of carbohydrates.3.Factors which may influence the bacterium's function of Cr(Ⅵ) elimination are explored. It showed that in conditions such as pH7.0～8.0, 30～35℃and initial bacteria dose 0.5g/L, CQMU-1 can demonstrate its optimal effects. Besides, it showed that CQMU-1 may utilize various ways, such as adsorption of static electricity, enzymatic catalytic conversion, flocculence, buffer action of pH and coprecipitation to perform its function of Cr(Ⅵ) elimination.In short, a strain belonged to Alcaligenes sp. with high Cr(Ⅵ) resistance and Cr(Ⅵ) elimination ability was isolated from highly Cr(Ⅵ) contaminated environment. It can get rid of Cr(Ⅵ) effectivly from wastewater and might be one of the optimal microorganisms used in the management of Cr(Ⅵ) contamination water and soil.
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