Cr(VI) reduction in naturally rich growth medium and sugarcane bagasse by Acinetobacter haemolyticus

Abstract

The potential of agricultural waste as substitute for rich-growth medium for bacteria during Cr(VI) reduction was investigated using the locally isolated Cr(VI) resistant-reducing strain of Acinetobacter haemolyticus and sugarcane bagasse. A. haemolyticus showed higher resistance to 100 mg/L Cr(VI) in Luria Bertani (>1010 CFU/mL) compared to sugarcane bagasse (106 CFU/mL). Higher Cr(VI) reduction by the SCB-immobilized bacteria (>90%) compared to in LB only (around 25%) clearly indicated the role of SCB in carrying out abiotic reduction of Cr(VI) as well as Cr(VI) adsorption. Nevertheless, Cr(III) was detected on the bacterial surface using Electron Spin Resonance (ESR) and electron microscopy (FESEM–EDX) analysis. The Cr(III) deposition occurred probably via complex formation with either carboxyl, hydroxyl or amide groups present on the bacterial cells surface as suggested from the FT-IR analysis. TEM analysis further showed Cr distribution at the membrane and cytosolic fractions. This work clearly demonstrated the role of bacteria in reducing Cr(VI) to Cr(III) as well as the potential of using agricultural waste material such as SCB to carry out abiotic Cr(VI) reduction.