Isolation and characterization of an environmental cadmium- and tellurite-resistant Pseudomonas strain

Abstract

A Pseudomonas strain (TeU), resistant to tellurite (TeO(2)(3)(-) and cadmium (Cd(2+)) ions, was isolated from heavy-metal-contaminated sediments by enrichment. Black precipitates, presumably the product of the reduction of tellurite, such as tellurium, occurred in cultures of the isolate after growth in medium containing tellurite. Quantitative determination of the TeO(2)(3)(-) concentration in the liquid culture demonstrated a decreased concentration of tellurite (to less than 100 µM) from initial concentrations of approximately 1,000 µM within 24 h of growth. Strain TeU was resistant to TeO(2)(3)(-) and Cd(2+) concentrations as high as 2,000 µM and 500 µM, respectively. Transposon mutagenesis of strain TeU resulted in mutants exhibiting Cd(2+) sensitivity (Strain BU21) and one with decreased ability to reduce tellurite (strain AU08). Strain BU21 was less tolerant to Cd(2+) (100 µM) compared with the wild-type strain TeU (500 µM) but was still able to reduce tellurite to 80% of that of strain TeU. Although strain AU08 possesses the ability for Cd(2+) resistance, it reduced less than 20% of the initial concentrations of tellurite compared with strain TeU. Genes encoding an HflKC complex and a putative metallopeptidase were associated with the bacterium's capacity for tellurite reduction and Cd resistance, respectively. The ability to reduce tellurite therefore may not be necessary for this bacterium's heavy metal and metalloid tellurite resisting ability.