Copper accumulation by sulfate-reducing bacterial biofilms.

Sulfate-reducing bacterial biofilms were grown in continuous culture. When exposed to medium containing 20 or 200 microM Cu, biofilms accumulated Cu. Energy-dispersive X-ray analysis (EDXA) showed that accumulation of Cu occurred in the form of sulfides while EDXA mapping of Cu and S in biofilm sections indicated that they were not uniformly distributed but located in the surface of the biofilm. While the polymer content of biofilm exposed to 20 microM Cu did not appear to increase relative to control Cu-free biofilms, biofilms exposed to 200 microM Cu accumulated carbohydrate and smaller amounts of protein throughout the incubation period. The mechanism of uptake, therefore, appeared to be precipitation of Cu sulfides at the biofilm surface or in the liquid phase followed by entrapment of precipitated Cu sulfide by the exopolymer-enhanced biofilm.