Screening Of A Zinc-Tolerant Strain And Its Characteristics In Resisting Zinc And Degradating Phenol

With the development of industry, waste water with heavy metals has become a prominent problem in the field of environmental protection. Zinc, as a kind of heavy metals, caused serious pollution and was toxic to environment. Once it entering environment could not be biodegradable. The majority would accumulate in the food chain cycle, eventually affect normal metabolism, and be harmful to human health. Using microbial treatment technology to remove heavy metals from waste water has become a new hotspot recently. It not only has the advantage of high speed but also does not create the second pollution as well as friendly to environment, which has aroused considerable interest during recent years.In this paper, A Zn-resisting bacterium with high concentration, isolated from the metal-polluted soil samples around Dexing copper mine, was studied. The purpose of this dissertation was to investigate the characteristics of a newly isolated strain DX-T3-03 wih ability to absorpt Zn2+. The morphological and physiological characterization and 16S rDNA molecular identification were carried out. The characteristics of strain DX-T3-03 gorwth and resistance to heavy metals were also investigated. Meanwhile, the bacterium could also degrade high concentration phenol. The optimum conditions for phenol degradation and interaction between Zn2+ and phenol in remediation were studied, too.Minimal inhibitory concentration of Zn2+ for this bacterium was as high as 3 600 mg/L. It was identified as Sphingomonas sp. belonging to a-Proteobacteria based on morphological and physiobiochemical characteristics and 16S rDNA sequence analysis. Growth and resistance to zinc of strain DX-T3-03 were investigated. Strain DX-T3-03 was sensitive to streptomycin and resistant to other antibiotics. The optimal conditions for both growth and resistance were as follows:35℃, pH 7.0, shaking speed 150 r/min,1 h, and 2 g/L (bacterial biomass). Under the optimal condition, adsorption rate of Zn2+ reached 80.93%. The dynamics of the bio-sorption was described by the pseudo second-order kinetic model. Both of Langmuir and Freundlich adsorption isotherms were applied in this study, indicating that the Langmuir model well fitted this experimental data and the Zn2+ adsorption by strain DX-T3-03 was a complex process including not only physical adsorption but also chemical adsorption.The absorption mechanism of Zn2+ was studied by FTIR, SEM-EDX. Results showed that the possible functional groups participated during the accumulation of Zn2+ were -OH,-NH2,-COOH and -PO43-. High concentration of zinc precipitated in the bacterial cell surface to achieve accumulation and detoxification, and Zn-resistance genes were located on its plasmid.The degradation of phenol by strain DX-T3-03 was investigated. The result showed that strain DX-T3-03 possesses high ability to degrade phenol. The optimum degradation conditions were 30℃, pH 7.0, rotating speed of 150 r/min and inoculum concentration of 20%. Strain DX-T3-03 could degrade phenol at a concentration as high as 600 mg/L completely within 24 h. Heavy metal ions such as Cu2+, Cd2+, Pb2+ and Ni2+ had different degrees of inhibition on phenol degradation, while no obvious effect of Zn2+ on phenol degradation was observed. Metabolic pathway research showed that S.DX-T3-03 could be induced to synthesize catechol 2,3-dioxygenase and phenol was catalyzed of strain DX-T3-03 through meta-cleavage pathway.