Screening Of Cr-resistant Strain From Soil And Study Of Its Biological Characteristics In Hechi Mining Area

Heavy metal mineral resources are abundant in China.However,various improper mining methods and heavy metal secondary process lead to heavy metal pollution of soil in many areas,especially in southern China.As one of the important pillar industries in Hechi city of Guangxi,non-ferrous metal industry has caused serious soil pollution by heavy metals.while promoting the rapid development of economy in recent years.To alleviate this problem,we collected four mine contaminated soils located in Dachang town,Nandan county,Hechi city of Guangxi,and analyzed the bacterial community composition by high-throughput sequencing technology.There were 39 different phyla in four samples.Among these phyla,Proteobacteria was the most abundant phylum in all samples.Acidobacteria,Actinobacteria,Planctomycetes,Firmicutes,Gemmatimonadetes,Bacteroidetes and Chloroflexi showed higher relative abundances than other phyla.In addition,a wide diversity of bacteria with the potential of bioremediation,such as Sphingomonas,Lysobacter and Gemmatimonas were detected in the tested mine contaminated soils.The results of bacterial community analysis will lay a good foundation for isolation of microorganisms with the potential of bioremediation in future.A novel bacterial strain tolerating high concentrations of heavy metal Cr(VI)was screened from heavy metals contaminated soil,which was named as Pseudomonas sp.Cr13 by 16 S r DNA sequencing.In this thesis,we conducted a series of in-depth studies on the biological characteristics of strain Cr13.The optimum temperature,culture time,rotation rate,p H,Na Cl concentration and temperature for growth were 30?C,18 h,150rpm,6,10% Na Cl for strain Cr13,respectively.Strain Cr13 was also resistant to Cd(II).The minimum inhibitory concentrations of Cr(VI)and Cd(II)for strain Cr13 were 250mg/L and 100mg/L,respectively.The mutant strains of UV mutagenesis test(treated with UV for 1min,4min and 5min)had not positive mutation,and their Cr(VI)tolerance was not as good as the original strain Cr13.In addition,antibiotics sensitivity of this strain was investigated.It was found that this strain was sensitive to nine types of antibiotics(such as gentamicin,ceftriaxone and ceftazidime),which would lay a good foundation for the choice of selective marker in genetic engineering modification of this strain.In this thesis,response surface methodology(Central Composite Design)was used to optimize the conditions of Cr(VI)removal from soil by strain Cr13.The initial concentration of Cr(VI),inoculum dose,organic content and culture time were selected as the major influence factors to optimize removal of Cr(VI).The optimum conditions were as: culture time of 7d,inoculum dose of 3.5%,organic content of 10%.Under the optimum conditions,the theoretical removal rate was 81.15%.In this thesis,the mechanism of Cr(VI)removal by Cr13 was studied.By comparing the removal rates of Cr(VI)between intracellular secretion and cell membrane in strain Cr13,the conclusion was as follows: the removal effect of Cr(VI)by cell membrane was stronger than that by intracellular secretion.The removal rates of Cr(VI)by cell membrane and intracellular secretion were 9.66% and 5.3% when Cr concentration was 50mg/L in the culture medium.