Screening of bacterial cells for biosorption of oxyanions: Application of micro-PIXE for measurement of biosorption

An attempt was made to isolate bacterial strains capable of biologically removing tungstate (WO42−) and perrhenate (ReO4−). Thirty-eight water samples were collected from various areas of Anzali lagoon, Iran. Initial screening of a total of 100 bacterial isolates, resulted in the selection of one isolate with maximum biosorption capacity of WO42− and ReO4−. It was tentatively identified as Bacillus sp. according to morphological and biochemical properties and named strain GT-83. WO42− and ReO4− uptake by Bacillus sp. GT-83 involved both inactive and active phenomena. The amount of WO42− (initial concentration 184 mg/l) removed from aqueous solution after 16 h by inactive and active phenomena was 26 and 194.5 μg/mg protein, respectively. The strain also removed ReO4− inactively (23 μg/mg protein). Bacillus sp. GT-83 tolerated high MIC of the oxyanions. The order of toxicity of the oxyanions to the bacterium was WO42− > ReO4− in solid media. The effects of increasing metal concentrations on the growth rate were determined in order to obtain precise patterns of resistance in liquid cultures. From the results of the oxyanions toxicity, inhibitory concentrations in solid media were higher than those in liquid media. Oxyanions biosorption was determined during the course of growth. Bacillus sp. GT-83 was capable of removing WO42− and ReO4− during the active growth cycle with a sorption capacity of 194.5 μg WO42−/mg protein and 137.1 μg ReO4−/mg protein. In view of the results of oxyanions accumulation experiments, it was concluded that Bacillus sp. GT-83 was not only tolerant to oxyanions, but it also bound considerable amounts of WO42− and ReO4− from the growth medium. The binding of tungsten and rhenium on the cell wall of Bacillus sp. GT-83 was confirmed with micro-PIXE.