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STUDIES ON THE BIOREMEDIATION OF CHROMIUM USING A BACTERIAL STRAIN ISOLATED
FROM A CHROMITE MINE
Divyasree C Prabhakaran, Jean Riotte and S Subramanian
Department of Materials Engineering and Indo-French Cell for Water Sciences, Indian Institute of Science,
Bangalore 560012, India
ABSTRACT
The potential of a bacterial strain isolated from water samples collected from a chromite mine in Odisha, India has
been assessed for the bioremediation of hexavalent chromium, a toxic environmental pollutant. The isolate was
identified as Sphingopyxis sp., a Gram negative bacterium, adopting molecular biological protocols and biochemical
characterisation techniques. Detailed investigations on the bio-removal of Cr (VI) were carried out using
Sphingopyxis sp. cells and the various parameters affecting the biosorption process were evaluated. About 55 %
biosorption of Cr (VI) was obtained using Sphingopyxis sp. bacterial cells and the residual chromium in solution was
found to be bio-reduced to the trivalent form, namely Cr (III). Thus, complete bioremediation of Cr (VI) could be
achieved using the mine isolate, with contributions from both biosorption and bioreduction mechanisms. The Cr(VI)
biosorption isotherm obtained for the isolate was found to follow a typical Langmuirian behaviour and the free
energy value of biosorption was determined to be ~-25 kJ/mol, indicative of involvement of chemical binding forces
in the bioremediation process. The chromium biosorption kinetics by the isolate followed a pseudo second order
reaction. The FTIR spectral studies revealed that carboxyl, hydroxyl, amino and phosphate groups were involved in
the biosorption process. X-ray photoelectron spectroscopic studies on the bacterial cells interacted with Cr (VI)
confirmed the presence of both Cr (VI) and Cr (III) on the cell surface. The electrokinetic studies revealed that the
surface potential of the bacterial cells were less electronegative subsequent to interaction with Cr(VI), compared to
the cells alone, which further testified to the binding of positively charged Cr(III) ions, formed by bioreduction of
Cr(VI), to the bacterial cell surface. A marginal shift in the iso-electric point obtained for the bacterial cells
interacted with Cr (VI), corroborated the involvement of chemical binding forces in the bioremediation process.
KEYWORDS
Bioremediation, Cr(VI), chromite mine, Sphingopyxis sp., biosorption, bioreduction