ACCUMULATION OF ZINC AND CADMIUM BY CYTOPHAGA-JOHNSONAE

Passive and active accumulation of zinc and cadmium by a common soil a nd freshwater bacterium, Cytophaga johnsonae, was studied using a radi o-tracer batch distribution technique. The effects of variation of pH (3-10), as well as of ionic strength (0.007 and 0.07 M) on passive acc umulation of the metals were examined. For both zinc and cadmium, accu mulation was mainly due to passive processes, such as surface adsorpti on and/or diffusion into the periplasm. However, at low zinc concentra tions, accumulation increased when glucose was added, suggesting an ac tive uptake; at higher zinc concentrations such uptake was not detecte d, probably because it was masked by the stronger sorption properties of the cell wall. Adsorption of the metals was pH dependent: at higher ionic strength, accumulation was enhanced at pH values above 7; at lo wer ionic strength, adsorption differed and was markedly higher, with increased accumulation between pH 5 and 8.