MANGANESE AND IRON OXIDATION BY FUNGI ISOLATED FROM BUILDING STONE

Acid and nonacid generating fungal strains isolated from weathered san dstone, limestone, and granite of Spanish cathedrals were assayed for their ability to oxidize iron and manganese. In general, the concentra tion of the different cations present in the mineral salt media direct ly affected Mn(IV) oxide formation, although in some cases, the additi on of glucose and nitrate to the culture media was necessary. Mn(II) o xidation in acidogenic strains was greater in a medium containing the highest concentrations of glucose, nitrate, and manganese. High concen trations of Fe(II), glucose, and mineral salts were optimal for iron o xidation. Mn(IV) precipitated as oxides or hydroxides adhered to the m ycelium. Most of the Fe(III) remained in solution by chelation with or ganic acids excreted by acidogenic strains. Other metabolites acted as Fe(III) chelators in nonacidogenic strains, although Fe(III) deposits around the mycelium were also detected. Both iron and manganese oxida tion were shown to involve extracellular, hydrosoluble enzymes, with m aximum specific activities during exponential growth. Strains able to oxidize manganese were also able to oxidize iron. It is concluded that iron and manganese oxidation reported in this work were biologically induced by filamentous fungi mainly by direct (enzymatic) mechanisms.