COBALT BINDING BY PROPIONIBACTERIUM-ARABINOSUM

Cobalt occurs in nature usually at very low concentrations and is acco mpanied by much higher concentrations of various metals. In order to a cquire cobalt under such unfavorable conditions, living systems evolve d effective uptake mechanisms based on high affinity to cobalt and dis tinguishing this element from among the others. Taking Propionibacteri um arabinosum as the bacterial model, which is known for its cobalt re quirement, the performance of microorganisms has been examined in this regard. By using radiolabeled cobalt and a filter technique, the upta ke capability of these bacteria at the stage of cobalt binding has bee n characterized in terms of binding capacity, and dissociation and equ ilibrium constants. Monovalent and divalent ions inhibit cobalt bindin g to bacteria. Divalent metal ions showed a competitive mode of inhibi tion, and the inhibitory constants for some of the toxic and biologica lly important divalent metal ions were determined. The chelating agent EDTA diminishes cobalt binding to bacteria already at concentration 1 0(-5) mu mol/l. Bacteria exposed to thermal shock at 60 degrees C incr eased several fold cobalt-binding capacity.