Transformation of Copper Salt by Wood Decaying Fungi

Abstract

When effective preservation tests are performed using wood specimens to which Coriolellus palustris, one of the oxalic acid producing fungi, is cultured, it has often been found that decay is limited to a particular portion where tissue is completely destroyed to make a hole, in the case of the specimen treated with preservatives containing copper salt. Under the microscopic observation of the decayed wood tissue light green colored, minutely crystalized substance is observed. Copper concentration is apt to be high around the hole. Accordingly, oxalic acid which is metabolized by the fungi is assumed to react on copper salts to form copper oxalate, and it is pressumed that there is a certain relation between the partially serious decay phenomenon and copper oxalate accumulation by fungi. In order to test these hypotheses a fundamental experiment was carried out by culturing the fungi in solution, agar and filter paper each of which contained copper salt with various concentration. Light green colored precipitate was obtained from the former two, and the surface of the filter paper was colored light blue. The substance precipitated by the fungi was identified to be copper oxalate by means of infrared absorption and X-ray diffraction methods. The surface of the filter paper colored light green was found to be remarkably rich in copper concentration by fluorescent X-ray analysis. It was found also that whereas the fungi cultured in water without any copper salt ingredient grew dispersed in the whole expanse of water, those in a solution containing copper salt grew concentrated like a concentric circle. The higher the concentration, the more distinct the denser, the smaller was the colony. It is noticed that untreated timber decays altogether shrunk. It is assumed that this is similar to the growth of fungi in water without copper salt ingredient. Timber treated with copper salt dacays partially but seriously. It appears that this is similar to the growth of fungi in copper salt solution.So it is only assumed, and so it only appears. It requires further studies to account for the decay of timber treated with copper salts.