MICROSCOPIC INVESTIGATIONS CONCERNING IN SITU OXALATE FORMATION BY THE BROWN-ROT FUNGUS PORIA PLACENTA

Basidiomycete fungi are important organisms for the biodegradation of wood. A main distinguishing feature of many brown-rot fungi is their ability to produce large quantities of oxalic acid. It is well known that the reaction between copper and oxalic acid can result in a detoxification of copper containing wood preservatives, due to the formation of insoluble copper oxalate. However, little information is available regarding the mechanism on a cellular level. The aim of this investigation was to determine in situ copper oxalate formation in order to localise the exact place of precipitation by means of light microscopy and scanning electron microscopy analysis. Additionally, the growth dynamics and minimal inhibitory concentrations on malt extract agar were investigated. Further; energy-dispersive X-ray analysis was used to obtain information about element distribution. Hereby a relative ion concentration not only of copper; but also calcium was measured in the hypha and the surrounding wood tissue. These results are helpful for a better understanding of metabolic strategies in the detoxification of copper in wood impregnated with protective agents.