BIOSORPTION OF CADMIUM, COBALT, NICKEL, AND STRONTIUM BY A BACILLUS SIMPLEX STRAIN ISOLATED FROM THE VADOSE ZONE

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 ma y be members of the same species. B. simplex ZAN-044 was studied along with Bacillus subtilis 168, and Escherichia coil K-12 (AB264), two we ll-characterized metal-sorbing bacteria, for the binding of Cd2+, Co2, Ni2+, and Sr2+. There was rapid (less than 1 h) uptake of 1 mu M met al by the three bacteria in the order Cd > Ni greater than or equal to Co > Sr, Binding followed a saturation isotherm at cation concentrati ons from 0.1 mu M to 1 mM, Cation binding was pH-dependent, with less binding at low pH. B. simplex ZAN-044 bound more metal than B. subtili s or E. coil, demonstrating that subsurface microorganisms can remove significant quantities of metals from solution and may be able to infl uence radionuclide and metal transport in the subsurface.