Isolation of Alkaliphilic Bacterium Citricoccus alkalitolerans CSB1 : AnEfficient Biosorbent for Bioremediation of Tannery Waste Water

Abstract

The present study designed to isolate and characterize an alkaliphilic chromate-resistant bacterium from crude salt and was identified as Citricoccus alkalitolerans CSB1 by 16S rDNA sequence analysis. The isolate could tolerate up to 25% NaCl (w/v) at pH 8.0-10.0 and 210 μg mL-1 of hexavalent chromium. Removal of Cr (VI) at concentration of 120 μg mL-1 was found to be about 98% within a period of 72 hours, at pH 9.0. The Cr (VI) removal efficiency after 60 hours was found 84.6%. The results on EDX analysis demonstrated surface binding as well as intracellular uptake of chromium by the bacterial cell. Zeta potential measurement indicates that the cell surfaces display a net negative charge at pH 10.0 (‒29.80 mV). This was supported by Fourier transform infrared spectroscopy analyses demonstrating that the cells are dominated by surface proton releasing ligands, including carboxyl, phosphoryl and amino functional groups. The negative zeta potential which might be facilitating Cr binding. Cr adsorption experiments further reveal that functional groups play a primary role in metal adsorption. Furthermore, the Cr (VI) sorption by bacterial cell surface fits well in Freundlich and Langmuir isotherm models with qmax value of 15.8 μgmg‒1 fresh biomass. Results demonstrated that the C. alkalitolerans CSB1 is an efficient bacterium for bioremediation of Cr (VI) contaminated effluents particularly in saline and alkaline environments.