The impact of surface attachment on cadmium accumulation by Pseudomonas fluorescens H2

Cadmium accumulation by Pseudomonas fluorescens H2 attached to glass surfac es and by cells free in suspension in maleate buffer was compared and showe d several major differences. The time to saturation of cells with Cd2+ was different for attached and free cells, although both showed biphasic uptake of Cd2+. The accumulation of Cd2+ by free cells was inhibited by the prese nce of zinc but remained several orders of magnitude higher than accumulati on by attached cells. The presence of Zn2+, however, did not inhibit Cd2+ u ptake by cells attached to the solid substratum. Cadmium uptake still incre ased with Cd2+ concentration for both free and attached cells in the presen ce of Zn2+. The accumulation of Cd2+ by both free and attached cells increa sed with pH up to pH 11. The presence of a metabolic inhibitor, carbomyl cy anide In-chlorophenyl-hydrazone, reduced the uptake of Cd2+ by free cells b y 40% but reduced uptake by attached cells by only 25%,. Approximately 65% of Cd2+ accumulated by cells free in suspension was associated with the cel l wall. 33% was present in the cytoplasm and only 2% was bound to exopolyme r. The results suggest that the characteristics of heavy metal accumulation by bacterial cells are substantially affected by attachment to solid surfa ces. (C) 2000 Federation of European Microbiological Societies. Published b y Elsevier Science B.V. All rights reserved.