Detoxification of hexavalent chromate by growing Paecilomyces lilacinus XLA.

In the study, the capability of Paecilomyces lilacinus XLA (CCTCC: M2012135) to reduce Cr(6+) and its main antagonistic mechanisms to Cr(6+) were experimentally evaluated. Activated growing fungus XLA efficiently reduced over 90% Cr(6+) in the media with Cr(6+) concentration below 100 mg L(-1) at pH 6 after 14 days. After 1-day exposure to 100 mg L(-1) Cr(6+), nearly 50% of Cr(6+) was reduced. Moreover, SO4(2-) stimulated Cr(6+) reduction, whereas other interferential ions inhibited Cr(6+) reduction. The interaction mechanisms between XLA and Cr(6+) mainly involve biotransformation, biosorption, and bioaccumulation, as detected by electron microscopy and chemical methods. The lower concentrations of Cr(6+) (5 and 50 mg L(-1)) stimulated the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH) level in XLA, respectively, but the higher concentration of Cr(6+) (150 mg L(-1)) decreased the enzymatic activities and GSH concentration. The results implied that SOD, CAT and GSH were defensive guards to the oxidant stress produced by Cr(6+). All these extracellular/intracellular defense systems endowed XLA with the ability to resist and detoxify Cr(6+) by transforming its valent species. The fungus XLA could efficiently reduce Cr(6+) under different environmental conditions (pH, interferential ions, and concentration). Moreover, XLA could endure the high concentration of Cr(6+) probably due to its high biotransformation capability of Cr(6+) and intracellular antioxidant systems for the detoxification of ROS generated by external Cr(6+). All these results suggested that the fungus XLA can be applied to remediation of Cr(6+)-contaminated environments.