Screening And Studying The Mechanisms Of Bacillus For Removing Heavy Metals In Water

The global environment is facing a huge challenge of heavy metal pollution.Heavy metals accumulated and existed in the ecosystem will threaten the health of human beings and the stability of ecosystem.Because of its high toxicity and non-biodegradability,it remains in the human body for a long time and may cause serious health-related diseases.Chemical technologies for heavy metal remediation has negative effects such as large amount of work,high cost and secondary pollution.Microbial remediation technology is considered to be the most potential remediation technology for heavy metal pollution due to its outstanding advantages such as high efficiency,low cost and environmental friendliness.Among them,the screening and mechanism study of bacteria with high removal efficient are beneficial to the removal or reduction of heavy metal pollution and the possibility of their absorption in the food web.Bacillus spp.are gram positive,ubiquitous in nature and recovered from all niches in the environment.These species have also been used to remove heavy metals.We screened bacteria with high removal efficiency of heavy metal(Cr,Ni,Pd,Cu and Ag)from 58 strains of Bacillus spp.afforded by the strain bank of the State Key Laboratory for Conservation and Utilization of Bio-Resources Yunnan University.All screened bacteria of the Bacillus spp.could remove five heavy metal from liquid solutions,but their removal rate vary quite a lot.The Ni(II)removal efficiency of 20%of the total isolated strains were higher than 90%.Among them,Bacillus tequilensis had the highest Ni(II)removal efficiency,reaching 96.06%;The Cr(?)removal efficiency of 22% of the total isolated strains were higher than 90%.The removal efficiency of B.horneckiae for Cr(?)is as high as 97.08%;The Pd(II)removal efficiency of 20% of the total isolated strains were higher than 90%.Among them,the removal efficiency of B.benzoevorans for Pd(II)was 92.20%.For the first time,three strains of Bacillus were reported to remove Ni(II),Cr(?)and Pd(II)with high efficiency.Among the selected Bacillus spp.,most strains with high removal efficiency of one heavy metal was not efficient in removing other heavy metals.the strains are specific for high-efficiency removal of heavy metals.The removal efficiencies of 58 Bacillus strains on Cu(II)and Ag(I)were less than 80%,which was not high.We used urea plates to isolate urease-producing bacteria from 58 Bacillus strains.Six strains could produce urease,which were B.firmus,B.psychrodurans,B.aryabhattai,Bacillus sp,B.pepperfolii sp.nov 1433 T,B.mobilis.It was first reported that B.psychrodurans,B.pepperfolii sp.nov 1433 T and B.mobilis could produce urease.Except B.pepperfolii sp.nov 1433 T,the removal rates of Ni(II)and Cr(?)of the other5 strains were all higher than 75%.Among them,the removal rates of Cr(?)and Ni(II)by B.mobilis were more than 90%,and the removal rate of Ni(II)by B.sychrodurans was as high as 95.39%.The tolerances of Bacillus spp.to five heavy metals were studied.The maximum tolerance concentration of 17 bacterial strains to Pd(II)was 450 mg/L,the maximum tolerance concentration of 1 bacterial strains to Ni(II)was 400 mg/L,the maximum tolerance concentration of 4 bacterial strains to Cu(II)was 350mg/L,the maximum tolerance concentration of 13 bacterial strains to Cr(?)was 300 mg/L,and the maximum tolerance concentration of 12 bacterial strains to Ag(I)was 100 mg/L.Bacillus strains with maximum tolerance concentration of 400 mg/L or 350 mg/L to Ni(II)all above 80% removal rate of nickel,indicating that the Bacillus bacteria with higher Ni(II)tolerance concentrations could remove Ni(II)efficiently.However,there is no obvious positive relationship between Bacillus strains with high tolerace concentrations of Cr(?),Cu(II),Ag(I),Pd(II)and their removal rates.The removal mechanism of 8 Bacillus strains with high Cr(?)removal efficiency was preliminarily studied.Among them,B.horneckiae and B.erophilus removed Cr(?)from liquid solution by biosorption.With the increase of initial Cr(?)concentration,the growth of living cells was inhibited and the removal ability decreased.The removal rate of B.horneckiae decreased from 97.8% to 18.45%,and that of B.erophilus decreased from 96.9% to 18.52%.Dry bacterial cells had higher biosorption capacity than living cells.Biosorption process was found to be initial concentration and p H dependent.A small amount of chromium ion were found on the surface of B.horneckiae bacteria by scanning electron microscopy The remediation mechanism of the other 6 Bacillus strains is complicated.