Reduction of hexavalent chromium in wastewater and three varying agricultural soils using a bacterial strain Bacillus sp. SR18 isolated from a contaminated field

Soil and water resources are often contaminated with different types of pollutants including metal ions due to indiscriminate discharge of industrial effluents. Hexavalent chromium [Cr(VI)] is one of such pollutants which has a tendency to adversely affect the environment. Microbial bioremediation is one of the cost-effective methods which might be used to remediate such metals. In current study, a bacterial strain, Basillus sp. SR18, having the potential to tolerate and reduce Cr(VI), was isolated from a soil of district Kasur Pakistan which has been repeatedly irrigated with wastewaters containing the tannery effluents. This strain had a good potential not only to tolerate the presence of Cr(VI) in the medium with MIC value of 20 mM but also to completely (>90%) reduce Cr(VI) even at its initial concentration of 20 mg L^-1. Basillus sp. SR18 was also effective for the Cr(VI) reduction in the presence of different concentrations of NaCl while, maximum Cr(VI) reduction was detected at pH 8.5. Moreover, SR18 was observed to reduce the Cr(VI) in varying agricultural soils and in real tannery wastewater. The reduction rate was significantly (p≤ 0.05) different between different treatments of tannery wastewater. Bioaugmentation of three different agricultural soils with the strain SR18 resulted into a significant but varying decrease in the level of Cr(VI) with the maximum decrease in sandy soil. This study presents the significance of Bacillus sp. SR18 as a potential living source for remediation of Cr(VI) in the soils and water resources.