Characteristics And Genetic Characterization Of Bacterial Pannonibacter Sp. Reduction Of Cr (vi) In The Study

Chromium, widely used in indurstry including leather tanning, electroplating, paint pigments and dye manufacturing, has caused serious environmental pollution. Cr(Ⅵ) is one of the most serious pollutants because of its carcinogenicity, teratogenicity and mutagenicity, Therefore, the remediation of chromium pollution is a challenging problem facing environmental protection all over the world. However, conventional physical and chemical methods are expensive and result in secondary pollution. At present, bioremediation has become one of the most promosing techniques in chromate contamination treatment.In this study, an effective Cr(Ⅵ) reduction strain was isolated from Cr(Ⅵ) contaminated soil. The strain was identified as Pannonibacter sp. based on its morphological and physiological-biochemical characteristics and the sequence analysis of 16s rDNA.In order to provide guidance for engineering, we studied the reduction of the resting cells of Pannonibacter sp.. And the research of chromate reductase was provided foundation for producing effective reduction engineering bacteria and constructing gene bank.The reduction of the resting cells of Pannonibacter sp. were investigated, and the results show that both the resting cells cultured in Cr(Ⅵ)-containing and Cr(Ⅵ)-free culture medium can effectivly reduce Cr(Ⅵ), almost with the same reduction rates; the reductibility of the resting cells is suppressed by oxygen which is essential for growth of the strain of Pannonibacter sp.. Without nutrient source, the resting cells in anaerobic condition reduce Cr(VI) fast, and has the greater reduction rate than that of resting cells in aerobic condition, which can hardly reduce Cr(Ⅵ). Moreover, the reductibility of the resting cells can be enhanced by the addition of some nutrients (like glucose or sodium lactate). In anaerobic condition, the reduction rate was increased by the glucose and sodium lactate at the same level, while the glucose almost cannot promote the reduction of Cr(Ⅵ) to Cr(Ⅲ). It is likely that the resting cells of Pannonibacter sp. reduce Cr(Ⅵ) to Cr(Ⅲ) by aggregation and co-ordination.The characteristics of Cr(Ⅵ) reductase was studied and the mechanisms account for Cr(Ⅵ) reduction were also diccussed. It was shown that cellular walls and membranes were the main sites where hexavaent chromium reduction took place, and changes in the permeability of cellular walls and membranes would affect the reductibility of hexavalent chromium reductase.The reductase is non-secretive and acts on inside the living cell.The genome DNA and plasmid were extrated from Pannonibacter sp.and E.coli.in this study. Combined with the clone of kanamycin resistance gene, it was concluded that the strain of Pannonibacter sp. has no plasmid and the chromate reductase gene is located in the genome DNA.