A zinc-resistant bacterium, Brevibacterium sp. strain HZM-1 which shows a high Zn2+-adsorbing capacity, was isolated from the soil of an abandoned zinc mine. Kinetic analyses showed that Zn2+ binding to HZM-1 cells follows Langmuir isotherm kinetics with a maximum metal capacity of 0.64 mmol/g dry cells and an apparent metal dissociation constant of 0.34 mM. The observed metal-binding capacity was one of the highest values among those reported for known microbial Zn2+ biosorbents. The cells could also adsorb heavy metal ions such as Cu2+. HZM-1 cells could remove relatively low levels of the Zn2+ ion (0.1 mM), even in the presence of large excess amounts (total concentration, 10 mM) of alkali and alkali earth metal ions. Bound Zn2+ ions could be efficiently desorbed by treating the cells with 10 mM HCl or 10 mM EDTA, and the Zn2+-adsorbing capacity of the cells was fully restored by treatment of the desorbed cells with 0.1 M NaOH. Thus, HZM-1 cells can serve as an excellent biosorbent for removal of Zn2+ from natural environments. The cells could grow in the presence of significant concentrations of ZnCl2 (at least up to 15 mM) and thus is potentially applicable to in situ bioremediation of Zn2+-contaminated aqueous systems.
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