Abstract
We conducted a study for enhanced biological rehabilitation of chromium-contaminated soils using a chromium-reducing and nitrogen-fixing bacterial species (Bacillus megaterium-ASNF3). The bacterial species was isolated from a chromium-rich land area, characterized, and employed under optimum conditions for the treatment of artificially prepared chromium-rich soil. The bacterium reduced Cr(VI) up to 86 % in a 60-day trial of incubation in the soil bioreactor. The nitrogenase activity of the bacterium yielded up to 486 nmol of ethylene/mL/h after an incubation period of 40 days when it was optimally cultured in growth medium at neutral pH and 30 °C. Although the nitrogen-fixing ability of the bacterium reduced significantly in the presence of 1000 ppm of Cr(VI), yet, the bacterium was proved to be a potential bio-fertilizer for enhancing nitrogen contents of the contaminated soil even under the higher chromium stress, together with the metal reduction. In the biologically treated soil, higher values of wheat growth variables were achieved. Application of metal-resistant B. megaterium-ASNF3 in selected situations rendered chromium-laden soils arable with significant increment in crop-yield parameters.
Highlights
Industrial activities and sewage sludge depositions have largely contributed to the spread of toxic metals in terrestrial and aquatic environments
We conducted a study for enhanced biological rehabilitation of chromium-contaminated soils using a chromium-reducing and nitrogen-fixing bacterial species (Bacillus megaterium-ASNF3)
The bacterial species was isolated from a chromium-rich land area, characterized, and employed under optimum conditions for the treatment of artificially prepared chromium-rich soil
Summary
Industrial activities and sewage sludge depositions have largely contributed to the spread of toxic metals in terrestrial and aquatic environments. The long-term depositions of metal-loaded effluents have transformed fertile land areas into non-arable lands. Agricultural activities on such lands would result in bioaccumulation of toxic metals in food chain (Lu et al 2011; Liu et al 2013). Wide industrial applications of Cr in textile, leather tanning, metal finishing, and inorganic chemicals’ manufacturing result into discharges of Cr-loaded effluents into the environment. The present study was designed to isolate a bacterium having the potential to fix N and reduce Cr simultaneously, from highly Cr-contaminated soil and to employ the bacterial species for enhanced and improved agro-rehabilitation of Cr-stressed soil
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