Accumulation of silver by growing and non-growing populations of Citrobacter intermedius B6

Abstract

Accumulation of silver is reported for growing and non-growing populations of Citrobacter intermedius B6. In non-growing cultures a maximum uptake of 4.35% (w/w) was observed at an initial silver concentration of 2111.2 μmol Ag+ l-1. In contrast the maximum uptake of silver by growing bacteria was 2.81% (w/w) at an effective concentration of silver of 217.8 μmol·l-1. Silver accumulation rates in both resting (460 μmol Ag+ g-1 per hour) and continuously grown (41 μmol Ag+ g-1 per hour) bacteria are higher than previously reported. Cell fractionation and electron microscopy of continuously grown bacteria indicated that accumulation of silver was associated with the cell envelope, in the form of dense deposits of macromolecular proportions. This observation discounts simple surface adsorption as the process of accumulation in growing cultures.