The effect of heavy metal-induced oxidative stress on the enzymes in white rot fungus Phanerochaete chrysosporium.

Prevalence of heavy metals in the living environment causes chemical stress and reactive oxygen species (ROS) formation in Phanerochaete chrysosporium (P. chrysosporium). However, the mechanisms involved in ROS defense are still under investigation. In the present study, we evaluated the effect of lead- and cadmium-induced oxidative stress on the activities of catalase (CAT), peroxidase (POD), lignin peroxidase (LiP), and manganese peroxidase (MnP). A time-dependent change in all enzyme activities was observed following exposure to 50 µM cadmium and 25 µM lead. The lowest values were recorded at 4 h after exposure. Both cadmium and lead inhibited CAT and POD. The cytochrome P450 (CYP450) levels increased under 50-100 µM cadmium or lead exposure and decreased when heavy metal concentration was under 50 µM; this suggested that ROS is not the only factor that alters the CYP450 levels. The cadmium removal rate in the sample containing 900 µM taxifolin (inhibitor of CYP450) and 100 µM cadmium was reduced to 12.34 %, 9.73 % lower than that of 100 µM cadmium-induced sample, indicating CYP450 may play an indirect but key role in the process of clearance of heavy metals. The pH of the substrate solution decreased steadily during the incubation process.

Facile green extracellular biosynthesis of CdS quantum dots by white rot fungus Phanerochaete chrysosporium.

This study details a novel method for the extracellular microbial synthesis of cadmium sulfide (CdS) quantum dots (QDs) by the white rot fungus Phanerochaete chrysosporium. P. chrysosporium was incubated in a solution containing cadmium nitrate tetrahydrate, which became yellow from 12h onwards, indicating the formation of CdS nanocrystals. The purified solution showed a maximum absorbance peak between 296 and 298 nm due to CdS particles in the quantum size regime. The fluorescence emission at 458 nm showed the blue fluorescence of the nanoparticles. X-ray analysis of the nanoparticles confirmed the production of CdS with a face-centered cubic (fcc) crystal structure. The average grain size of the nanoparticles was approximately 2.56 nm, as determined from the full width at half-maximum (FWHM) measurement of the most intense peak using Scherer's equation. Transmission electron microscopic analysis showed the nanoparticles to be of a uniform size with good crystallinity. The changes to the functional groups on the biomass surface were investigated through Fourier transform infrared spectroscopy. Furthermore, the secretion of cysteine and proteins was found to play an important role in the formation and stabilization of CdS QDs. In conclusion, our study outlines a chemical process for the molecular synthesis of CdS nanoparticles.