Narrow Results

Salmonella typhimurium was cultured either in minimal or in enriched medium in the presence of increasing concentrations of Ni²⁺, Cd²⁺, Hg²⁺ and exhibited a much higher sensitivity to Hg²⁺ than to the other two metal ions. After 24 h growth in minimal medium the yield decreased by 50% in the presence of 0.26 mM Ni²⁺ and by 60% in the presence of either 0.08 mM Cd²⁺ or 0.0008 mM Hg²⁺. After growth in enriched medium, the yield decreased by 80% in the presence of 15 mM Ni²⁺ or 5 mM Cd²⁺ and by 65% in the presence of 0.03 mM Hg²⁺. Cytochromes were used as a probe to investigate the effect of metals on membrane proteins. Increasing metal concentrations led to increasing reductions in the amount of all cytochromes (b₅₆₀, b₅₉₅ and d) although to various extends, depending on the metal and on the cytochrome. At metal concentrations that drastically diminished the cell yield, cytochrome b₅₉₅ was the most affected in the presence of Ni²⁺ or Cd²⁺, while cytochrome d was the most affected in the presence of Hg²⁺. Results indicated that Hg²⁺ distinguished itself from Cd²⁺ and Ni²⁺ by the concentration range tolerated by the bacterium as well as by the effect observed on the cytochromes.