Mineral transformations by fungi in culture and in soils

Abstract

Although micro‐organisms are regarded as the principal agents of mineral cycling in soils, the role of bacteria has generally been emphasized, while that of fungi has been neglected. Fungi are able to transform the majority of elements in vitro but whether they play an important role in soil is as yet unknown. There is sufficient circumstantial evidence from soil studies to suggest that fungi may under certain conditions nitrify and oxidize reduced forms of sulphur. Their role in denitrification and sulphate reduction process is more speculative. While they appear incapable of nitrogen fixation, fungi undoubtedly play a major role in the mineralization of organic N,P, and S in soils, in the solubilization of insoluble phosphates, and participate in oxidation of manganese. Perhaps one of their most important roles is in the dissolution of silica and rocks thus releasing ions into the soil solution during weathering. The ability of fungi to oxidize elements in vitro does not compare with that of the chemoautotrophic bacteria. On the other hand in vitro activity tells us little about the activity of an organism in the soil. At present our appreciation of the part played by fungi in mineral cycling in soils is limited by the techniques available, but there is little doubt that they have a major role to play in the cycling of elements other than carbon.

Fungi of a forest soil nitrifying at low pH values

“…Properties of the site other than soil reaction, such as humus and clay content or litter quality, may possibly determine which hypothesis is correct for acid softs. Knowledge of heterotrophic nitrifying bacteria and fungi has been reviewed [10,11]. Heterotrophic nitrification has also been identified in a forest soft [12].…”

Inorganic Sulfur Oxidation by Aureobasidium pullulans

“…Heterotrophic S oxidation is in many ways analogous to heterotrophic nitrification. Both processes involve fungi and heterotrophic bacteria, and although the involvement of these organisms has long been recognized, their role was overlooked as soon as chemoautotrophic Nand S-oxidizing bacteria were discovered (15,19).…”

“…A wide range of heterotrophic microorganisms, including actinomycetes (21), heterotrophic bacteria (8,12,13), and fungi (18,19,20), are able to oxidize various forms of inorganic S. Wainwright and Killham (20) recently showed that the soil fungus Fusarium solani (Martius Saccards) can oxidize So to S2032-, S4062-, and S042in vitro and in autoclaved and nonsterile soils, but did not demonstrate whether or not the process is enzymatic.…”