Inoculation of chromium-tolerant bacterium LBA108 to enhance resistance in radish ( Raphanus sativus L.) and combined remediation of chromium-contaminated soil.

Cr(VI) has been a carcinogen for organisms and a hazard to human health throughout the food chain. To explore a cost-effective and efficient method for removing Cr(VI), a Cr-resistant strain named LBA108 was isolated from the soil of a molybdenum-lead mining area. It was identified as Microbacterium through biochemical tests and 16S rDNA sequence analysis. Following 48 hours of incubation in LB culture medium containing 60 mg L-1 Cr(VI), the LBA108 strain exhibited reduction and adsorption rates for Cr(VI) at 96.64% and 15.86%, respectively. The removal mechanism was subsequently confirmed through Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction analysis. In an experimental setup, radish seedlings were cultivated as test crops under varying levels of Cr stress (ranging from 0 to 7 mg L-1 ) in a hydroponic experiment. With the inoculation of the LBA108 strain, the fresh weight of radish seedlings increased by 2.05 times and plant length increased by 34.5% under 7 mg L-1 Cr stress. In addition, the plant produced more antioxidant enzymes/enhanced antioxidant enzyme activities such as superoxide dismutase and catalase to prevent oxidative stress. Under Cr stress (6 mg L-1 ), the accumulation of Cr in rhizomes of radish seedlings increased compared to the control group by 91.44%, while the absorption of Cr by leaves decreased by 52.10%. These findings suggest that the LBA108 strain possesses bioremediation capabilities as a microbial-phytoremediation option for Cr-contaminated soil.