Metal tolerance and biosorption capacity of Bacillus circulans strain EB1.

A heavy-metal-resistant bacterium Bacillus sp., strain EB1 was isolated from heavy-metal-contaminated soil in the southeast region of Turkey. Based on 16S ribosomal DNA sequencing, the microorganism was closely related to Bacillus circulans. Minimal inhibitory concentrations of metals (MICs) for the bacterium were determined. Bacillus EB1 exhibited high MIC values for metals and a large spectrum of antibiotic resistance. The order of toxicity of the metals to the bacterium was Cd=Co>Cu>Ni>Zn>Mn in solid media. The effects of increasing metal concentrations to the growth rate were determined in order to obtain precise patterns of resistance in liquid cultures. From the results of heavy metal toxicity, inhibitory concentrations in solid media were higher than those in liquid media. Metal biosorption was determined during the course of growth. B. circulans strain EB1 was capable of removing 90% of Mn, 68% of Zn, 65% of Cu, 45% of Ni and 40% of Co during the active growth cycle with a specific biosorption capacity of 25, 22, 20, 13 and 12 mg/l, respectively. Since Bacillus cells could grow in the presence of significant concentrations of metals and due to high metal biosorption capacity in aerobic conditions, this bacterium may be potentially applicable in in situ bioremediation of heavy-metal-contaminated aqueous systems.