Research On The Microbial Diversity Of Cr(Ⅵ)-polluted Soil And The Isolation Of Cr(Ⅵ)-reducing Strains

The Cr(Ⅵ)-polluted soil samples taken from a Ferroalloy company in Hunan were studied by DGGE and RFLP technology. The bacterial diversity of Sample1was the highest. Rhodobaca bogoriensis, Limnobacter thiooxidans, Halomonas sp., Azoarcus sp., Dethiobacter alkaliphilus and Hydrogenophaga sp. were found in all the three samples.PCA analysis showed that the composition of microbial community tends to be close for samples which have similar elemental composition. The bacterial diversity of Sample1and4were more similar in the three samples studied.CCA analysis showed that, Thiomicrospira sp., Marinobacter alkaliphilus, Brevundimonas sp., Sphingomonas hunanensis, Azoarcus sp., Hydrogenophaga sp., Indibacter alkaliphilus and Oxalobacteraceae bacterium found in the the three samples were more relevant to Cr.Eight strains, which can reduce high concentration Cr(Ⅵ) in alkaline solution, were isolated from the soil samples. The optimum conditions for the growth of five selected strains and factors affecting their Cr(Ⅵ) reduction efficiency such as temperature, pH value, concentration of Cr(Ⅵ) and heavy metal ions were studied. The results show that, the optimal pH value (about9.0) and temperature (about30℃) for Cr(Ⅵ) reduction of Exiguobacterium sp. Y2(except for temperature), Bacillus sp. Y6(except for pH value), Exiguobacterium sp. Y7, Pseudochrobactrum saccharolyticum strain W1and Pseudomonas aeruginosa strain W5generally coincide with the optimal growth conditions. Furthermore, the growth of strains and the reduction efficiency of Cr(Ⅵ)(except for Exiguobacterium sp. Y2) would be inhibited with the increase of Cr(Ⅵ) concentration. The existence of Co2+, Cu2+, Mn2, Ni2+or Zn2+would inhibit the reduction efficiency of Cr(Ⅵ) of Pseudochrobactrum saccharolyticum strain W1; The existence of Co, Cu2+or Mn2+would enhance the Cr(Ⅵ) reduction efficiency of Pseudomonas aeruginosa strain W5; The existence of Co2+would enhance the Cr(Ⅵ) reduction efficiency of Exiguobacterium sp. Y2.