A METHOD TO INCREASE SILVER BIOSORPTION BY AN INDUSTRIAL STRAIN OF SACCHAROMYCES-CEREVISIAE

Ag+ biosorption by an industrial strain of Saccharomyces cerevisiae wa s investigated. Older (96 h old) biomass had half the biosorption capa city of younger (24 h old) biomass (0.187 and 0.387 mmol Ag+/g dry mas s respectively). Comparisons of cell walls isolated from biomass of ei ther age indicated that chemical composition and Ag+ biosorption capac ity varied little over the time span examined and that cell walls from either age of culture had small Ag+ biosorption capacities compared t o whole cells of a similar age. Silver-containing precipitates were ob served both on the cell wall and within the cell, indicating that intr acellular components sorbed Ag+ The concentration of these precipitate s within the cell appeared visually to decrease with age in Ag+-expose d cells. Incorporation of L-cysteine into the growth medium resulted i n biomass with increased silver biosorption capacities, protein and su lphydryl group content. Increasing the concentration of L-cysteine in the growth medium from 0 to 5.0 mM increased silver biosorption from 0 .389 to 0.556 mmol Ag+/g dry mass Isolated cell walls of biomass grown in supplemented media also showed a possible link between silver bios orption capacities, protein and sulphydryl group content. No precipita tes were observed in silver-exposed biomass that had been grown in the presence of 5.0 mM L-cysteine.