Cobalt binding by Propionibacterium arabinosum

Abstract

Cobalt occurs in nature usually at very low concentrations and is accompanied by much higher concentrations of various metals. In order to acquire cobalt under such unfavorable conditions, living systems evolved effective uptake mechanisms based on high affinity to cobalt and distinguishing this element from among the others. Taking Propionibacterium arabinosum as the bacterial model, which is known for its cobalt requirement, the performance of microorganisms has been examined in this regard. By using radiolabeled cobalt and a fitter technique, the uptake capability of these bacteria at the stage of cobalt binding has been characterized in terms of binding capacity, and dissociation and equilibrium constants. Monovalent and divalent ions inhibit cobalt binding to bacteria. Divalent metal ions showed a competitive mode of inhibition, and the inhibitory constants for some of the toxic and biologically important divalent metal ions were determined. The chelating agent EDTA diminishes cobalt binding to bacteria already at concentration 10-5 μmol/l. Bacteria exposed to thermal shock at 60 °C increased several fold cobalt-binding capacity. © 1995 Elsevier/NRA.