Ca2+ and SO42- accelerate the reduction of Cr(VI) by Penicillium oxalicum SL2.

Some ions in soils may affect the growth and metabolism of microorganisms and subsequently alter the remediation efficiency of Cr(VI). Here, the effects of different Ca2+ and SO42- levels on the reduction of Cr(VI) by Penicillium oxalicum SL2 were investigated. The results showed that Cr(VI) reduction by P. oxalicum SL2 in potato dextrose liquid (PDL) medium was accelerated by the presence of exogenous Ca2+ and SO42-. The Cr(VI) reduction rates were increased by 52.5% (200 mg L-1 Ca2+ treated) and 55.9% (2000 mg L-1 SO42- treated), respectively. High concentration of Ca2+ in medium resulted in the production of calcium oxalate crystals, which was contributed to the adsorption of chromium. In addition, X-ray absorption near-edge spectroscopy (XANES) analysis showed that P. oxalicum SL2 could reduce the toxicity of Cr(VI) by synthesizing cysteine (Cys) and reduced glutathione (GSH). The decrease of thiol compounds (Cys and GSH) in P. oxalicum SL2 mycelia treated with SO42- proved the alleviation of oxidative stress. In conclusion, exogenous Ca2+ could reduce the damage of Cr(VI) to P. oxalicum SL2 by maintaining the integrity of cell wall, and the addition of SO42- alleviated the Cr(VI) toxicity to P. oxalicum SL2, thus accelerating the reduction of Cr(VI).