Prospective of chromium (VI) reduction under in vitro and in vivo conditions and stimulation of antioxidant defense of cowpea under the exposure of Cr (VI)

Release of industrial waste into agricultural land affects its productivity. Among different remediation strategies (physico-chemical vs. biological), biological strategy, e.g. symbiotic association of microbes and plants, is among the most efficient ones to control/remediate pollution in agricultural land. The present study was performed to assess potential role of bacterial strain B6 for detoxification of Cr (VI) into Cr (III) and ameliorate toxicity of chromium (VI) in cowpea plants. Bacterial strain B6 completely reduced Cr (VI) at pH 6-7, 25-30 degrees C and 200-300 mu g/ml Cr (VI). Bacterial strain B6 reduced Cr (VI) into Cr (III) [31.5 mu g/ml of Cr (III) in supernatant and 71.3 mu g/ml in debris]. Chromium reductase enzyme produced by strain B6 completely reduced Cr (VI) to Cr (III), compared to cell debris which did not show Cr (VI) reduction. PCR amplification revealed presence of Cr (VI) reductase gene (Chr) in Bacillus species B6 showing a fragment of around 300 bp. MDA and antioxidant levels showed an increasing trend with increase in dose rate of Cr (VI). Bacterial inoculation in general, showed maximum photosynthetic pigments and enhanced antioxidants which together optimized growth of cowpea when grown in pot soils amended with different dose rates of Cr (VI). Improvement in cowpea growth, photosynthetic pigments and antioxidants were due to complete reduction of Cr (VI) to Cr (III) by Bacillus species B6 after 20 days of growth of cowpea. Chromium (VI) reduction and antioxidant expression under in vitro and in vivo conditions were responsible for overall growth of cowpea.