Potential of novel bacterial consortium for the remediation of chromium contamination

This study was aimed to examine the efficiency of a novel bacterial consortium on the reduction of toxic hexavalent chromium [Cr(VI)] to non-toxic trivalent Cr [Cr(III)]. Six Cr(VI)-resistant bacteria (IS1-IS6) were isolated from a tannery waste disposal site at Mount Barker, South Australia, of which three viz., IS1, IS2 and IS3 were selected based on Cr(VI) reduction ability in minimal salt medium. The isolates were identified as Bacillus endophyticus (IS1), Microbacterium paraoxydans (IS2) and Bacillus simplex (IS3) by 16S rRNA gene sequencing. All three isolates were able to tolerate chromium (Cr(VI), 300–400 mg L⁻¹), arsenic (As(V), 1,000 mg L⁻¹), copper (Cu(II), 300–400 mg L⁻¹) and lead (Pb(II), 1,000 mg L⁻¹). The isolates were evaluated both as an individual and as a consortia for Cr(VI) reduction in minimal salt medium and storm water, both spiked with 100 mg Cr(VI) L⁻¹. In both cases, the rate of Cr(VI) reduction was found to be significantly higher in the bacterial consortium inoculation (t _½ = 8.45 for minimal salt medium; 6.02 h for storm water), compared to inoculation with individual isolates (t _½ = 53.3–115.5 h for minimal salt medium; 8.77–9.76 h for storm water). The rate of Cr(VI) reduction in both minimal salt medium and storm water was found to be higher in bacterial consortium inoculation (IS1 + IS2 + IS3) than in individual isolate inoculation. This experiment demonstrated that bacterial consortium prepared by using B. endophyticus, M. paraoxydans and B. simplex was more effective in Cr(VI) detoxification than application of individual bacterium. This experiment also proved that a bacterial consortium was more effective in Cr(VI) detoxification than the application of individual bacterial strain.