Biosorption of cadmium, cobalt, nickel, and strontium by a Bacillus simplex strain isolated from the vadose zone

Abstract

A subsurface Gram-positive, endospore-forming, filamentous bacterium, designated ZAN-044, was isolated from a depth of 96.2 m in the vadose zone of the Hanford Site in Washington State. A phylogenetic analysis of the 16S rRNA gene sequence of strain ZAN-044 revealed it to be 99.5% similar to Bacillus simplex strain DSM 1321, indicating that they may be members of the same species. B. simplex ZAN-044 was studied along with Bacillus subtilis 168, and Escherichia cell K-12 (AB264), two well-characterized metal-sorbing bacteria, for the binding of Cd2+, Co2+, Ni2+, and Sr2+. There was rapid (less than 1 h) uptake of 1 μM metal by the three bacteria in the order Cd > Ni ≥ Co > Sr. Binding followed a saturation isotherm at cation concentrations from 0.1 μM to 1 mM. Cation binding was pH-dependent, with less binding at low pH. B. simplex ZAN-044 bound more metal than B. subtilis or E. coil, demonstrating that subsurface microorganisms can remove significant quantities of metals from solution and may be able to influence radionuclide and metal transport in the subsurface.