Response of bacterial strains isolated from a uranium mining waste to heavy metal stress

Two bacterial strains, Iso2 and Iso3, were cultured from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. The 16S rRNA gene sequence analysis demonstrated that these strains belong to the genus Arthrobacter of Actinobacteria. In this work, a combination of wet chemistry, spectroscopic, microscopic and microbiological methods were used to assess the stress response of these strains to heavy metals. The studied strains, Arthrobacter sp. Iso2 and Iso3, tolerate -lead, -nickel, and -uranium in concentrations up to 0.5 mM, 18 mM, and 1 mM respectively. As was demonstrated by X-ray powder diffraction (XRD) analysis, the cells of these two strains precipitate lead as lead sulfide (galena). Transmission electron microscope (TEM) showed that these precipitates are localized mainly at the cell surface. Dead/live staining indicated that 60% of the lead-treated cells are viable. Polyacrylamide gel electrophoretic (PAGE) analysis of total bacterial proteins showed different profiles between the Pb-treated and the -untreated (control) cells. The amount of a 55 kDa protein was higher in lead-treated cultures than in the control cultures. The origin of sulfide involved in lead precipitation will be discussed in term of microbial activity .