Silver accumulation inPseudomonas stutzeri AG259

Abstract

Silver toxicity toPseudomonas stutzeri AG259 was strongly dependent on the NaCl concentration in the medium, which reduced the availability of Ag⁺ by precipitation as AgCl. Accumulation of Ag⁺ by growing cultures was low being ⩽ 7.5 nmol (mg dry mass)⁻¹ over all treatments examined. The presence of NaCl in the growth medium did not markedly affect the amounts of Ag accumulated by the cells but influenced toxicity as manifest by a lag period which was greatest at low NaCl concentrations (⩽ 0.1% mass/vol.). In NaCl-free medium,P. stutzeri did not grow in the presence of 0.5 mM AgNO₃ in contrast to Ag-free controls. The majority of Ag accumulation by resting cells ofP. stutzeri occurred within 1 min of incubation and there was little difference in uptake capacities between cells previously grown in the absence or presence of AgNO₃. Lowest amounts of Ag uptake by resting cells occurred when suspended in 1 mM Mes pH 6.5, containing 1% (mass/vol.) NaCl. Prior exposure ofP. stutzeri to Cu(NO₃)₂ resulted in a marked reduction in Ag uptake when suspended in 1 mM Mes pH 6.5, containing 0.5 mM AgNO₃.