Intracellular distribution of cadmium during the growth of Abortiporus biennis on cadmium-amended media

Accumulation of heavy metals in the mycelium of Abortiporus biennis and their effect on oxalate oxidase activity

Abortiporus biennis belongs to a basidiomycete fungi with the unique ability to degrade oxalate using enzyme oxalate oxidase. Oxalate oxidase (OXO) from Abortiporus biennis is an intracellular oxalic acid-induced enzyme, which catalyses the degradation of oxalic acid to carbon dioxide and hydrogen peroxide. OXO activity was stimulated by all the heavy metals tested (copper, manganese, lead and cadmium) after addition as water-soluble salts to A. biennis fungal cultures. Manganese ions stimulated OXO activity to the greatest extent among the tested metal ions. In the presence of manganese ions, an elevated concentration of oxalate was also detected in the fungal culture after 7 days of cultivation. The manganese, lead, and cadmium ions were accumulated by the A. biennis mycelium. Among them, lead was accumulated to a great extent. It was observed that the accumulation of lead ions occurred in the vicinity of the A. biennis hyphal cell wall.

Morphological changes and bioaccumulation in response to cadmium exposure in Morchella spongiola, a fungus with potential for detoxification

Morchella is a genus of edible fungi with strong resistance to Cd and the ability to accumulate it in the mycelium. However, the mechanisms conferring Cd resistance in Morchella are unknown. In the present study, morphological and physiological responses to Cd were evaluated in the mycelia of Morchella spongiola. Variations in hyphal micro-morphology including twisting, folding and kinking in mycelia exposed to different Cd concentrations (0.15, 0.9, 1.5, 2.4, 5.0 mg/L) were observed using scanning electron microscopy. Deposition of Cd precipitates on cell surfaces (at Cd concentrations > 2.4 mg/L) was shown by SEM-EDS. Transmission electron microscopy analysis of cells exposed to different concentrations of Cd revealed the loss of intracellular structures and the localization of Cd depositions inside/outside the cell. FTIR analysis showed that functional groups such as C=O, -OH, -NH and -CH could be responsible for Cd binding on the cell surface of M. spongiola. In addition, intracellular accumulation was observed in cultures at low Cd concentrations (< 0.9 mg/L), while extracellular adsorption occurred at higher concentrations. These results provide valuable information on the Cd tolerance mechanism in M. spongiola and constitute a robust foundation for further studies on fungal bioremediation strategies.