Microorganisms are effective for decontamination of Cr(VI) in contaminated wastewater. However, some ions in soils may affect the growth and metabolism of microorganisms and influence the remediation effectiveness of Cr(VI) in contaminated soil sequentially. Here, fungi Penicillium oxalicum SL2 was used to investigate the impact of Ca²⁺ and SO₄^2- on Cr(VI) reduction process. Results showed that addition of Ca²⁺ and SO₄^2- increased the biomass of P. oxalicum SL2 and promoted the secretion of oxalic acid and citric acid, thus accelerating the reduction of Cr(VI). The maxmium rate of Cr(VI) reduction was 3.17 mgL^-1h^-1 (40 mg L^-1 Ca²⁺ treated) and 2.58 mgL^-1h^-1 (2000 mg L^-1 SO₄^2- treated), respectively. The results of scanning electron microscope (SEM) showed that the hyphae of P. oxalicum SL2 were thicker and grew better with the addition of Ca²⁺ and SO₄^2- than those in the control group. Furthermore, regular shaped calcium oxalate crystals were detected in P. oxalicum SL2 mycelia in Ca²⁺ treated goup through electron dispersion spectroscopy (EDS) and X-Ray powder diffraction (XRD) analyses. Meanwhile, the results of X-ray absorption near-edge spectroscopy (XANES) evidenced an increace of cysteine, cystine and glutathione (GSH) in P. oxalicum SL2 mycelia with the addition of SO₄^2-, which might induce the reduction of Cr(VI). In conclusion, addition of Ca²⁺ could reduce the damage of Cr(VI) to P. oxalicum SL2 by maintaining the integrity of cell wall, and the transformation of sulfur from SO₄^2- to cysteine, cysteine and GSH during restoration process was conducive to elevate the reduction efficiency of Cr(VI).

Key words: Penicillium oxalicum SL2; Cr(VI) reduction; transformation