Effects of Salt Concentration on the Intracellular Cadmium Content of and the Cadmium Uptake by a Highly Cadmium-tolerant, Moderately Halophilic Pseudomonas sp.

Abstract

The intracellular cadmium (Cd) content was measured with early stationary phase cells of a highly Cd-tolerant moderately halophilic bacterium Pseudomonas sp. No. 40 cultivated in 1 M and 3 M NaCl medium containing 0 to 2500μg of CdCl₂/ml. It was found that the Cd contents were greatly affected by the NaCl concentration of the medium. When the bacterium was cultivated in the 1, 2, 3, and 4 M NaCl medium containing 1500μg of CdCl₂/ml, the intracellular Cd content was 25.0, 4.1, 3.1, and 2.0 mg Cd per g of dry cells, respectively. The intracellular Cd content decreased with increases of NaCl concentration of the medium. The fact seems to reflect Cd-tolerance of the bacterium towards the growth in the medium of different NaCl concentration. It is worthwhile to note that the bacterium showed the highest Cd-tolerance (in 3 M NaCl) and the lowest Cd content among the bacteria so far known. The bacterial cells grown in the 1 M NaNO₃ and 1 M Na₂SO₄ medium accumulated 1.8-1.3 times as much Cd²⁺ as those in the 1 M NaCl medium in the presence of 50-200μg of CdCl₂/ml. It would also explain the difference in the Cd toxicity in the medium of NaNO₃, Na₂SO₄, or NaCl.