Hexavalent chromium bioreduction by chromium-resistant sporulating bacteria isolated from tannery effluent

The main polluting source of heavy metal contamination of water is the leather tanning industry, which uses chrome powder and discharges it into the nearby ecosystem. In this investigation, chromium-resistant bacterial strains were isolated and characterized from tannery effluent. Based on morphological and biochemical characterization, the predominant sporulating Bacillus sp. was isolated and identified as Bacillus subtilis based on 16S rRNA gene sequencing. Chromium degradation by the bacterial strain was evaluated using the flask culture method at three different concentrations (300, 600, and 900 µg/ml) of Cr (VI), and the reduction potential of the isolated bacterium was analyzed by Atomic Absorption Spectrophotometry. A maximum reduction of approximately 78% was found at 24 hrs of incubation at pH 7 and at a constant temperature of 30°C. More than 50% of the Cr(VI) was decreased in 24 hours when the Cr(VI) concentration varied from 300 to 900 g/ml. FTIR analysis showed the involvement of hydroxyl and amine groups in chromium adsorption. As an outcome, this strain could be a promising bioagent for the environmentally friendly elimination of toxic Cr(VI) from polluted environments.