The impact of surface attachment on cadmium accumulation by Pseudomonas fluorescens H2.
Cadmium accumulation by Pseudomonas fluorescens H2 attached to glass surfaces and by cells free in suspension in maleate buffer was compared and showed several major differences. The time to saturation of cells with Cd(2+) was different for attached and free cells, although both showed biphasic uptake of Cd(2+). The accumulation of Cd(2+) by free cells was inhibited by the presence of zinc but remained several orders of magnitude higher than accumulation by attached cells. The presence of Zn(2+), however, did not inhibit Cd(2+) uptake by cells attached to the solid substratum. Cadmium uptake still increased with Cd(2+) concentration for both free and attached cells in the presence of Zn(2+). The accumulation of Cd(2+) by both free and attached cells increased with pH up to pH 11. The presence of a metabolic inhibitor, carbomyl cyanide m-chlorophenyl-hydrazone, reduced the uptake of Cd(2+) by free cells by 40% but reduced uptake by attached cells by only 25%. Approximately 65% of Cd(2+) accumulated by cells free in suspension was associated with the cell wall, 33% was present in the cytoplasm and only 2% was bound to exopolymer. The results suggest that the characteristics of heavy metal accumulation by bacterial cells are substantially affected by attachment to solid surfaces.