Effect of Salt Concentration on the Cadmium Tolerance of a Moderately Halophilic Cadmium Tolerant<i>Pseudomonas</i>sp.

Abstract

The cadmium (Cd) tolerance of 41 strains of halophilic bacteria with different salt-requirements was surveyed. Their tolerances showed the vast range of from below 50 to 2,500 μg CdCl2 per ml, and a highly Cd-tolerant, moderately halophilic Pseudomonas sp. No. 40 was found. The effects of the concentrations of NaCl, NaNO3 and Na2SO4 on the Cd-tolerance of the bacterium were examined by turbidity measurement and viable counting. It was noted that the Cd-toxicity was greatly affected by the NaCl concentration of the medium: poor growth was seen at 2,000 μg CdCl2 per ml and no growth at 2,500 μg CdCl2 per ml in 1 M NaCl medium whereas moderate growth was observed in 2 to 4 M NaCl medium containing 2,500 μ CdCl2 per ml, showing a decrease of the Cd-toxicity with an increase in the NaCl concentration. On the other hand, the Cd-toxicity was apparently enhanced by NaNO3 and Na2SO4: the bacterium failed to grow at as low as 200 μg CdCl2 per ml in 1 to 2 M NaNO3 medium or at 500 μg CdCl2 per ml in 1 M Na2SO4 medium. Also, the toxicity was measured as cell death, and accommodation to Cd required an extended lag time that varied with both the concentration of Cd and that of salts.