Ni and Cd Biosorption Capacity and Redox-Mediated Toxicity Reduction in Bacterial Strains from Highly Contaminated Soils of Uzbekistan.

In this study, Ni and Cd resistant 18, 11Uz, and Uz_5 strains were isolated from soils contaminated with heavy metals in the Samarkand and Kashkadarya regions (Uzbekistan), and tested to remove Ni and Cd ions from the environment via biosorption. The biosorption capacity of these strains was observed under in vitro conditions. The biosorption process was highly dependent on the growing conditions, with the highest biosorption rate observed after 300 min of incubation at pH 7.0, and 40 °C. The presence of functional groups such as S=O, NH, and COOH in the biosorbing microorganisms was confirmed by IR spectroscopy. The adsorption capacity decreased when the initial metal concentration was increased and was enhanced with higher microbial biomass. 11Uz strain was found to alter the toxic oxidation state of Ni and Cd cations, while 18 and Uz_5 strains reduced the toxicity of Ni cations only by changing their oxidation state. It was confirmed in our studies that the three selected bacterial strains actively participated in the detoxification of Cd through the synthesis of cysteine amino acid.