Identification Of Lead And Zinc-tolerant Microbial Floras And Their Performances Of Lead And Zinc Removal

The microorganisms living for a sufficiently long period in heavy metal contaminated environment can develop metal resistant capacities.Isolation and acclimation of such microorganisms is therefore an effective way at present to obtain microbial remediation resources with high efficiencies.Application of a single microorganism species,however,usually has limitations as its developed metal tolerant ability can be easily altered under different environmental conditions.In comparison,a microflora consisting of a number of microorganisms undergoing a long duration period of adaptation and symbiosis can possess systematic functions with high stabilities,and have thus considerably high potential in intensifying the effect of phytoremediation.In the present study,orthogonal experiments were carried out to compare the difference of their performances in removal of lead and zinc by culturable rhizospheric microfloras in a lead-zinc tailing area amended with and without an organic fertilizer.The experimental conditions were optimized for acquisition of high efficient metal-tolerant microbial floras.The nutrient solution-sand culture tests were conducted to analyze the effect of the microbial flora on seed germination and seedling growth of R.communist as well as relevant mechanisms of heavy metal accumulation.The high-throughput sequencing technology was applied to investigate the structure and diversity of tolerant microbial flora.The main results are summarized as follows:1)Under the combined stress of lead-zinc contamination,the culturable microflora obtained from the rhizosphere amended with organic fertilizers acted efficiently on removal of lead,while the effect of organic fertilizer application on microflora with respect to zinc removal was insignificant.The observed highest lead and zinc removal rates of the microflora from the organic fertilizer amending treatment(LJ)was 40.2%and 12.7%,respectively,higher than those from the control plot(LJO).The examined factors,including the concentration of lead-zinc,medium types,etc,had apparently affected the capacities of microflora to remove lead and zinc,among which the medium types had the highest impact.The optimum concentration of lead-zinc,inoculation dose,incubation time and culture medium for culturing flora LJ related to removal of lead and zinc were 50 mg/L,1.0 mL,6 days and Beef-peptone,respectively.2)The two groups of resistant microbial floras acquired from the optimum culture conditions showed different impact on the growth and development for R.communist in early stages.For the seed germination,inoculation of Beef-peptone flora(bacteria)has some promoting actions to its germination,Martin flora(fungi)presents inhibiting effect.In the stage of seeding growth,Beef-peptone flora is beneficial to the growth of plant height,while Martin flora is more beneficial for the seedling root’s growth.R.communist seedling’s capability in accumulation and transportation of zinc are superior to lead,and the heavy metal is accumulated in roots chiefly.Both the two groups of floras showed distinct inhibitory effect on the absorption of zinc,having little effect towards the absorption of lead.Under the stress of higher lead-zinc concentration(100 mg/L),inoculation of two groups of floras is more beneficial for plants’ upward transformation for lead and zinc.3)The rhizospheric resistant bacteria of R.communist is abundant,and dominant phylum is Proteobacteria,dominant classes are Cyanobacteria and Bacilli,dominant genus are Ensifer,Cupriavidus.Under the stress of lead-zinc with 100mg/L,the richness of resistant bacterial community has changed somewhat,and the relative abundance of dominant bacteria also presents downtrend yet not changing its dominant position,a few class groups presents the phenomenon of increasing relative abundance.However on the whole,resistant bacterial flora present a certain stability.For the insufficiency of sequencing depth,the tested fungi flora is very sole.Ascomycota,Sordariomycetes,Fusarium are dominant fungus at the phylum,class and genus levels in term of colony,taking up 99.9%of the total fungi.The stress of lead-zinc with 100mg/L has significant lowering actions on the relative abundance for Fusarium,and highly significant boosting actions on that of Aspergillus.