Tolerance and biosorption of copper and zinc by Pseudomonas putida CZ1 isolated from metal-polluted soil

A strain of Pseudomonas sp. CZ1, which was isolated from the rhizosphere of Elsholtzia splendens obtained from the heavy-metal-contaminated soil in the north-central region of the Zhejiang province of China, has been studied for tolerance to copper (Cu) and zinc (Zn) and its capacities for biosorption of these metals. Based on 16S ribosomal DNA sequencing, the microorganism was closely related to Pseudomonas putida. It exhibited high minimal inhibitory concentration values (about 3 mmol (CuL-1)-L-. and 5 mmol (ZnL-1)-L-.) for metals and antibiotic resistance to ampicillin but not to kanamycin. Based on the results of heavy metal toxicity screening, inhibitory concentrations in solid media were lower than those in liquid media. Moreover, it was found that the toxicity of Cu was higher than that of Zn. Pseudomonas putida CZ1 was capable of removing about 87.2% of Cu and 99.8% of Zn during the active growth cycle, with specific biosorption capacities of 24.2 and 26.0 mg(.)L(-1), respectively. Although at low concentrations, Cu and Zn slightly damage the surface of some cells, P. putida demonstrated high capacities for biosorption of Cu and Zn. Since P. putida CZ1 could grow in the presence of significant concentrations of metals and because of its high metal uptake capacity in aerobic conditions, this bacterium may be potentially applicable in bioreactors or in situ bioremediation of heavy-metal-contaminated aqueous or soil systems.