Microbial Diversity Analysis Of Chromium Contaminated Soil And Research On Characteristics Of Hexavalent Chromium Reducing Bacterial

In recent years, severe chromium pollution incidents have occurred frequently inchina. To environment workers, chromium contaminated soil, caused by chromiumresidue and other facters, become a problem to be solved. Compared with the traditionalmanagement method, bioremediation of chromium contaminated soil with no secondarypollution, and with in situ remediation which does not affect the original soil ecologicalenvironment conditions, has gradually became the treatment approaches favored by theresearchers. However, due to start lately, impact on soil environment, and unclear of theaction mechanism ect, the technology is not yet fully mature, and large scaleapplications.To explore the extent and manner coming from chromium on microbial communitystructure in the chromium contaminated soil, comparative analysis the single carbonsource utilization and microbial species richness through utilizing the BiologECOPlate^TMand PCR-TGGE techonologies. In addition, a Cr（VI） reduction bacteriawhich has relatively high reduction ability was isolated and identified. For providing thecontrol parameters in practical engineering application, get the optimum reductionconditions in the lab through changing environmental conditions. Finally, the reducingsubstances of No.1strain was separated and processed, and preliminary analyse of thereduction mechanism was done.Biolog ECOPlate^TMand polymerase chain reaction （PCR）-TGGE experimentalresults show that: there are some reducing bacteria in the selection of chromium residuecontaminated soil. Although the biodiversity of chromium residue contaminated soil hadget back a certain extent, biodiversity is still less than not contaminated soil. What`smore the community structure and advantage populations have also changed.7reducion bacteria were isolated from chromium residue contaminated soil,amogng them, the reduction ability of No.1strain was stronges, and the rest can tolerateand reduct a certain concentration of Cr（VI）. The No.1strain was Gram-positivebacteria,and16SrDNA identification results demonstrated it was Bacillus cereus. TheNo.1strain enter stationary phase after cultured26h and maintain30h, which wasbenefit to the conduct of hexavalent chromium reduction reaction. When temperature is35centigrade and pH is5, the reduction rate of Cr（VI） get maxmum.Most important ofall, pH value near7after24h in defferent initial pH of the chromium-containing solution. The reduction rate of No.1strain is positively correlated with the concentrationof cells, while it reduce with the initial concentration of Cr（VI）. When initial Cr（VI）concentration get500mg/L, The No.1strain loss Cr （VI） the reduction ability.Observed by SEM, the cell surface of No.1strain was significantly absorbed somesubstances in theculture containing Cr（VI）. The reduction ability compared the differentcomponents of the cell, the extracellular secretion is best, which was able to reductCr（VI）completely restore; followed by membrane fragments. Further experiments foundthat extracellular secretion contain some of Cr（VI） reductase and metabolites. WhileIntracellular secretion reduction is reductase. In addition, there may be some functionalgroups on the cell membrane, and they involved in coordination reaction with Cr（VI）,and then reduce soluble Cr（VI） in liquid. The dormancy body of No.1strain does nothave the ability of Cr（VI） reduction, indicating that the bacteria does not have anindependent defense system and Cr（VI） reduction process is closely related to otherphysiological functions of bacteria.