Tolerance and Removal Mechanisms of Heavy Metals by Fungus Pleurotus ostreatus HAAS

Fungus Pleurotus ostreatus HAAS can tolerate and remove heavy metals from water. Among three heavy metals tested, the removal of Pb was the most efficient (99.9-100.0%), followed by Cd (45.9-61.1%), and Cr (29.4-64.5%). The uptake of heavy metals by the fungus varied and was dependent on the element. Pb was found to be transported primarily into the fungal cell wall (68.2-91.2% of the total), which was much higher than the insoluble form (20.1-32.7%), and the maximum intracellular concentration of Pb was found to be 119,830.4 mg kg(-1). In the cases of Cd and Cr, their insoluble forms were the main products of the reaction with the fungus, which accounted for 30.0-39.1 and 19.6-37.4% of the total. P. ostreatus HAAS produces oxalic acid, and this production is stimulated by Pb and Cr but inhibited by Cd. Parallel experimental results indicated that the concentration of the soluble metals in solution decreased with the increase of oxalic acid, which further suggested that oxalic acid played a partial role in the removal of the soluble heavy metals by chelation. These results revealed that this species of fungus has a variety of response mechanisms to the presence of heavy metals in solution.