Heavy Metal Tolerance and Biotransformation of Toxic Metal Compounds by New Isolates of Wood-Rotting Fungi from Thailand

ABSTRACT

Eighteen isolates of wood-rotting fungi isolated from Thailand were screened for the ability to produce metal-containing crystals from zinc, copper, cadmium and lead salts-amended culture medium. Five isolates (MR40, KYO, WR3, WR4 and WR5) were able to produce mycogenic crystals in 0.5% (w/v) heavy metal compound amended plates. The crystals were further investigated by scanning electron microscopy equipped with energy dispersive X-ray microanalysis (SEM-EDXA) and identified by X-ray powder diffraction (XRPD). The selected fungi were found to be capable of transforming zinc sulfate (ZnSO₄·7H₂O) into zinc oxalate dihydrate (C₂O₂Zn·2H₂O), copper sulfate (CuSO₄·5H₂O) into copper oxalate hydrate (C₂CuO₄·xH₂O), cadmium sulfate (3CdSO₄·8H₂O) into cadmium oxalate trihydrate (C₂CdO₄·3H₂O) and lead nitrate (Pb(NO₃)₂) into lead oxalate (PbC₂O₄). Two of the selected strains (Fomitopsis cf. meliae and Ganoderma aff. steyaertanum) have not been previously reported to have heavy metal compound transformation abilities. These results provide further evidence that wood-rotting fungi can remove heavy metals from a metal-amended substrate by precipitation as metal oxalates: wood-rotting fungi could therefore be applied for detoxification of heavy metal pollution.

KEYWORDS:

• Bioremediation
• biotransformation
• heavy metal
• wood-rotting fungi

Funding

The authors gratefully acknowledge the Graduate School of Chulalongkorn University for a Post-Doctoral Fellowship, Ratchadapisek Somphot Endowment Fund. G.M. Gadd gratefully acknowledges an award under the 1000 Talents Plan with the Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, China.