Reduction of Chromium(VI) by Marine Bacterium Brevibacillus laterosporus Under Varying Saline and pH Conditions

Abstract

A halotolerant chromate [Cr(VI)]-resistant bacterium, CrRPSD40, isolated from marine sediments of Paradip port, Odisha, India, was identified and used in Cr(VI) reduction study. Based on biochemical characterization and 16S rRNA gene sequencing, the bacterium CrRPSD40 was identified as Brevibacillus laterosporus, with 97.7% homology to B. laterosporus. The bacterium has a high Cr(VI) resistance (up to 2,100 mg/L) and a high salt tolerance (up to 11% w/v NaCl) capacity. Bacterial growth in the presence of Cr(VI) (100 and 500 mg/L) showed a relatively longer lag phase (0-12 h) and a shorter exponential phase (12-72 h) compared with growth without Cr(VI). Cr(VI) reduction by B. laterosporus was studied at various ranges of pH (4.0-10.0) and NaCl (1-11% w/v) concentration, at 35 degrees C temperature, and at 130 rpm agitation speed. The optimum saline and pH condition for better growth and Cr(VI) reduction by CrRPSD40 were found to be 3% w/v NaCl and 8.0, respectively. Under the optimum condition, CrRPSD40 exhibited efficient Cr(VI) reduction as much as 92% and > 50% of 100 mg/L Cr(VI) in just 120 and 60 h of treatment, respectively. Comparative changes in bacterial cell surface morphology due to interaction with Cr(VI) were evident from the field emission scanning electron microscope-energy dispersive X-ray spectroscopy (FESEM-EDX) and Fourier transform infrared (FTIR) analyses. The present investigation described the significant reduction potential of the native marine B. laterosporus (CrRPSD40) under the wide range of saline and pH conditions for its successful implementation in Cr(VI) detoxification of a saline metal-polluted environment.