Screening Identification Of Heavy Metal-Resistant Actinomycetes And Research On Biosorption Of Zn(Ⅱ) By Strain CCNWHX 72-14

13 heavy metal-resistant actinomycete strains were screened out from 55 tested strains, which were isolated from lead zinc ore tailings inLongnan of Gansu province and sewage irrigation area in northern suburb of Xi'an. Three kinds of methods including filter paper inhibitory prefigurative, primary scanning on solid plates and repeated scanning in liquid medium were used and compared. The determinations of heavy metal-resistant strains of the three methods were agree with each other, while the resistant level showed great diversity. Maximum resistant levels (MRL) of the 13 anti-metal strains to seven heavy metals: Cu²⁺,Hg²⁺,Pb²⁺,Ni²⁺,Zn²⁺,Cd²⁺,Cr⁶⁺ were then determined through more detailed ionic concentration gradient. The MRL (mmol/L) of strain CCNWHX 72-14 to the following metal ions was: Zn²⁺:13, Cu²⁺:0.8, Ni⁺:0.6, Pb²⁺:2, Hg²⁺:0.07, Cd²⁺:0.6, Cr6:0.3.Strain CCNWHX 72-14, which showed much higher degree of resistance to Zn²⁺ than other strains, was identified as a new member of Streptomyces ciscaucasicus by former researcher. Taxonomic positions of the other 12 heavy metal-resistant strains were identified by polyphasic taxonomy, which was consisted of morphological, cultural, biochemical and physiological characteristics and 16S rRNA gene sequence analysis. The dendrogram of numerical taxonomy found on biochemical and physiological characteristics was compared wth phylogenetic tree based on similative 16S rRNA gene sequences. Strain groups deviations through the two analytic methods seemed to be consistent to a certain extent.Growth of strain CCNWHX 72-14 was well in the presence of 2 mmol/L Zn²⁺ and the optimum cultural time proved to be 7 d. Effects of single factors on the biosorption capacity of Zn²⁺ by this strain during delaied exponential phase such as initial metal concentration, initial pH, inoculation dose, agitation speed and fermentation temperature were determined. The effect of fermentation temperature was quite slight and the following experiments were conducted at 28℃. L9(34) orthogonal experiments were designed founded on results of single tests and the optimum conditions for zinc biosorption were definited to be: initial Zn²⁺ concentration:150 mg/L, initial pH: 5, inoculation dose: 1%, agitation speed: 60 rpm/min. Validation tests demonstrated good repeatability of the zinc biosorption progress at the optimum conditions and the maximum biosorption capacity of Zn²⁺ under experimental terms was 51.05mg/g (0.781 mmol/g). Preliminary investigation for biosorption mechanism of Zn²⁺ were performed, which proved that the removal of zinc ions were on account of Znic biosorption, of which the adsorption in cells were predominant absolutely.The biosorption characteristics of Zn²⁺ using live and dead cells of Streptomyces ciscaucasicu strain CCNWHX 72-14 as biosorbents have been investigated in the present research. Optimum conditions for biosorption were determined to be: pH adjusted to 5, agitated at 90 rpm and at a dose of 2 g/L. For initial zinc concentrations of 1-150 mg/L, batch biosorption data of live biomass preferred to be simulated with Freundlich model while those of dead strain fit Langmuir isotherm well. Experimental maximum biosorption capacity turned out to be 42.75 mg/g (0.654 mmol/g) for living material and 54 mg/g (0.826 mmol/g) for dead sorbents, respectively. The pseudo second-order equation was chosen to describe the time course biosorption process. In contrast to live biosorbents, dead biomass seemed to have higher desorption efficiency at pH 1. Competitive biosorption revealed the order of competing metal ion to be: Cu²⁺ > Cd²⁺ > Ni+. FT-IR analysis indicated that more functional groups were involved in the biosorption process of dead adsorbents, compared with those linked to live biomass. Taken together, it can be concluded that dead cells of CCNWHX 72-14 were better biosorbents than live ones.13 heavy metal resistant strains were screened out and identified in this study, which supported more new resources for bioremediation. Both the optimization for zinc biosorption coditions by proliferous cells and the studies on equilibrium and kinetic biosorption of Zn²⁺ onto live and dead bisorbents, have laid the foundation for further investigation on ionic biosorption mechanism and its use in environmental bioremediation application.