Study On Zinc Adsorption Behavior Of Zn-resistant Strains With Different Existing Forms

In the study,two microbial strains(named S3 and S13)which can tolerate high concentration of zinc,were isolated from the soil.Then the Zn2+ adsorption behavior of the two strains in bilfilm and planktonic forms was compared.The results were shown as follows:(1)Based on the 16SrDNA sequences analysis,the strain S3 was identified as Sphingobacterium caen,and the S13 isolate was Rhizobium metallidurans.The results showed that the minimum inhibitory concentration of Zn2+ for S3 and S13 strains was 500mg/L and 300mg/L.Respectively,when the initial concentration of Zn2+ was 100mg1L,200mg/L and 300mg/L,the maximum adsorption rate for S3 was 48.8%,30.6%and 22.5%,and the corresponding value for S13 was 42.2%,27.4%and 14.5%.(2)For both S3 and S13,the higher the initial concentration of Zn2+was,the lower the yield of the biofilm produced.Within 48 hours,when the initial concentration of Zn2+ was 100mg/L,200mg/L,300mg/L,for strain S3,the maximum adsorption rate for planktonic bacteria was 34.8%,21.8%,14%,the rate for biofilm was 41.2%,27.3%,20.26%;for strain S13,the maximum adsorption rate for planktonic bacteria was 21.8%,14.7%,5.1%,the corresponding value for biofilm was 28.1%,20.2%,11.4%,which means the Zn2+ adsorption capacity of biofilm was stronger than planktonic bacteria.The laser confocal microscope was used to investigate biofilms morphology,the results showed that extracellular polymer plays an important role in the process of Zn2+adsorption of biofilm.For planktonic bacteria of two strains,about 20%of the Zn2+ was adsorbed by the intracellular accumulation,which suggests that Zn2+ was accumulated both by the intracellular accumulation and extracellular adsorption.For biofilm bacteria,the proportion of intracellular accumulation was less than 10%,which means that the Zn2+ was mainly accumulated by extracellular adsorption:(3)There is not much difference between the adsorption process of biofilm bacteria and planktonic bacteria,which suggests that the presence form of bacteria had no significant effect on the Zn2+ adsorption capacity of the bacteria.For strain S3,the biosorption capacity of live cells was stronger than that of dead cells;but for S13,the biosorption capacity of dead cells was higher than live cells.The adsorption equilibrium time of live cells was longer than dead cells for both S3 and S13.Moreover,the second-order kinetic model was more suitable to describe the biosorption process for both live and dead cells of the two strains.After adsorption,FTIR of the two bacteria was analyzed,the result showed that O-H,N-H,C-O were the main adsorption functional groups for strain S3,O-H,N-H,C=O,C-O were the main adsorption functional groups for strain S13.For the two strains,the polysaccharose content was higher than protein in the composition of planktonic bacteria EPS.But,the protein content was higher than polysaccharose in the composition of biofilm EPS.And the adsorption rate for biofilm EPS of the two strains was higher than that of the planktonic bacteria.For strain S3,the equilibrium adsorption rate for planktonic bacteria EPS was 32.4%,the rate of biofilm EPS was 37%;for strain S3,the equilibrium adsorption rate for planktonic bacteria EPS was 29.1%,the corresponding value for biofilm EPS was 34.5%.In addition,the second-order kinetic model was more suitable to describe the biosorption process for EPS.