Diversity Of Heavy Metal Resistant Bacteria Of Baiyangdian Lake And Screening Of Cr(â…¥) Transformation Strains

Baiyangdian Lake is one of the few natural big lakes in North China. The discharge of urban and industrial sewage from Beijing, Baoding and surrounding area caused severe pollution of this lake. Among them, Pb(II), Cu(II) and Cr(VI) are the major heavy metal pollutants. As microorganisms play a key role in the geobiochemical recycle of metal elements and bioremediation of heavy metal pollution, it is very important to study on the bacterial diversity and other ecological indicators in the sediment of Baiyangdian Lake.In this study, 12 water samples and 9 sediment sampleswere collected from 12 sampling sites and 9 group ecological factors were determined, which include longitude and latitude, temperature(℃), DO(mg), Chl-a(mg/m3), TN(mg/m3), TP(mg/m3), Cu(II)(μg/L), Pb(II)(μg/L) and Cr(IV)(μg/L). Heavy metal resistant bacrteria were acclaimed and screened, as results, 54 Pb(II) resistant strains(80 μg/m L), 46 Cu(II) resistant strains(80 μg/m L) and 39 Cr(VI) resistant strains(100 μg/m L) strains were obtained from sediment samples. Phylogenetic positions of the heavy metal resistant strains were determined by amplifying, sequencing and phylogeny analysis based on 16 S r DNA. It demonastraed that these strains belong to 13 species distributed in 7 genera Pseudomonas, Stenotrophomonas, Brevundimonas, Comamonas, Enterobacter, Delftia and Lysinibacillus.The relationships between the heavy metal resistant strains and the biological factors were analysed by carring out PCA analysis using the software PSAT 3. And the following results could be found:Lysinibacillus is the unique 100 μg/m L Cr(IV) resistant genus, it is widely distributed;The species composition and distribution range of Pb(II) resitant and Cu(II) resitant strains are very similar, Pseudomonas and Stenotrophomonas are the highest tolerance genera, which indicated that the heavy metal resitant strain is not single resistant; Stenotrophomonas is the only genus which can survive in three kinds of heavy metals environment.In the second part of this research, the Cr(VI) transformation strains were screened from 397 Cr(VI) resistant bacterial strains deposited in our laboratory. 15 strains of supra-60% Cr(VI) removal efficiency were obtained by preliminary screening. And 4 strains of supra-70% Cr(VI) removal efficiency were obtained by secondary screening. The primary investigation of optimum removal conditions and transformation mechanism were carried out on these 4 strains. Results showed that the optimum Cr(VI) transformation temperature of strains Cr-11, Cr-22, Cr-28 and n-9 is 37 ℃, the optimum p Hs were 7, 8, 9 and 9, respectively. All the four strains transform Cr(VI) to Cr(III) by enzyme action, and the enzymes are intracellular.