Biotransformation of Chromium (VI) via a Reductant Activity from the Fungal Strain Purpureocillium lilacinum

Abstract

Industrial effluents from chromium-based products lead to chromium pollution in the environment. Several technologies have been employed for the removal of chromium (Cr) from the environment, including adsorption, ion-exchange, bioremediation, etc. In this study, we isolated a Cr (VI)-resistant fungus, Purpureocillium lilacinum, from contaminated soil, which could reduce chromium. We also characterized a reductant activity of dichromate found in the cellular fraction of the fungus: optimal pH and temperature, effect of enzymatic inhibitors and enhancers, metal ions, use of electron donors, and initial Cr (VI) and protein concentration. This study also shows possible mechanisms that could be involved in the elimination of this metal. We observed an increase in the reduction of Cr (VI) activity in the presence of NADH followed by that of formate and acetate, as electron donor. This reduction was highly inhibited by EDTA followed by NaN₃ and KCN, and this activity showed the highest activity at an optimal pH of 7.0 at 37 °C with a protein concentration of 3.62 µg/mL.

Keywords: Cr (VI) reduction; Purpureocillium lilacinum; bioremediation; biotransformation; enzymes; heavy metal.

Figure 1

Reductant activity in different cell fractions of the fungus P. lilacinum at different incubation times. 28 °C, pH 7.0, 100 rpm. (a) Without NADH+ as electron donor, (b) With NADH+ 10 mM.

Figure 2

Effect of pH on crude reductant activity in the mixed membrane fraction of Purpureocillium lilacinum determined in different buffers (pH 5.0–9.0) at 37 °C, 1 h of incubation, and 100 rpm.

Figure 3

Effect of temperature on crude reductant activity in mixed membrane fraction of Purpureocillium lilacinum. pH 7.0, 1 h of incubation, and 100 rpm.

Figure 4

Effect of different initial concentrations of Cr (VI) on crude reductant activity in the mixed membrane fraction of Purpureocillium lilacinum. 1 h of incubation, pH 7.0, 100 rpm, and 37 °C.

Figure 5

Effect of metal ions on crude reductant activity in the mixed membrane fraction of Purpureocillium lilacinum. 1 h of incubation, pH 7.0, 100 rpm, and 37 °C.

Figure 6

Effect of inhibitors on crude reductant activity in mixed membrane fraction of Purpureocillium lilacinum. 1 h of incubation, pH 7.0, 100 rpm, and 37 °C.

Figure 7

Effect of electron donors on crude reductant activity in the mixed membrane fraction of Purpureocillium lilacinum. 1 h of incubation, pH 7.0, 100 rpm, and 37 °C.

Figure 8

Effect of different enzyme concentrations on crude reductant activity in the mixed membrane fraction of Purpureocillium lilacinum. 1 h of incubation, pH 7.0, 100 rpm, and 37 °C.

Figure 9

Gradual conversion from Cr (VI) to Cr (III) with green precipitate observed in the mixed membrane fraction of Purpureocillium lilacinum after 15 days at 37 °C with 20 mg/L Cr (VI).