Removal of soluble cadmium by bacterial isolates

Abstract

Five of 346 strains of cadmium-resistant isolates (100 ug/ml) were selected and named CdR-87, CdR-98, CdR-205, CdR-207 and CdR-273. They produced exopolysaccharides and resisted cadmium at the concentration of 500, 400, 750, 400 and 750 (ug/ml), respectively. By some identification tests, they might be classified as Enterobacter sp. Optimum pH and optimum temperature for growth and EPS production of those test bacterial isolates were 5-9 and 30-40 C, respectively. In addition, the long incubation period (from 24h to 72h) of these culture resulted in the higher production of EPS (from 1 to 30 mg per mg cells). In contrast, addition of cadmium into the medium reduced the amount of EPS production of most of the bacterial isolates. When the Cd concentrations were increased from 10 to 50 and 100 ug/ml, Cd uptakes were found to be increased but the percentages of uptake were decreased. Immobilization of cells of those isolates with calcium alginate was performing the percentage of Cd biosorption by EPS was more than 90. However, the effect of calcium alginate alone on Cd absorption could not be excluded. The rate of Cs absorption was very rapid during the first 10 minutes of the interaction, Regeneration of immobilized cell was performed two to three times. It was found that the effcient of EPS in Cd absorption was decreased. Those bacterial isolates might be suitable for further investigations in the removal of soluble Cd.