Copper is an essential metal ion for eukaryotic life and must strictly be regulated as excess levels can cause oxidative damage, enzyme inhibition and denaturation, interruptions in nutrient transport and even cellular death. Copper-based wood treatments have efficacy against a wide range of biological organisms including decay fungi and are used in the majority of preservative formulations for outdoor exposure. For most fungal species, copper can be toxic at elevated concentrations, such as those present in preservative treated wood. Despite this, a group of brown-rot fungi has been identified as “copper-tolerant” as they are not only able to tolerate high concentrations of copper but can even degrade copper-treated wood and result in major economic loss to treated wood products in-service. The mechanism of copper tolerance by these fungi remains largely unknown despite decades of ongoing research. Understanding how copper-tolerant fungi interact with copper during initial attack of copper treated wood is needed and studies visualizing copper ion movement in wood are lacking. We used synchrotron-based X-ray fluorescence microscopy (XFM) to study copper distribution before and after fungal exposure to copper-tolerant, Fibroporia radiculosa, and copper-sensitive, Gloeophyllum trabeum. Copper-treated blocks exposed to G. trabeum showed no changes in copper distribution over time. Copper-treated blocks exposed to F. radiculosa showed reductions in copper distribution in the top face of the blocks over time. Additional ions (Ca, Mn, and Fe) were also visualized. We also used sub-micron XFM (2-ID-E) to visualize intracellular copper ion distribution in wood cell walls exposed to F. radiculosa and G. trabeum. Copper was translocated to the lumen surface in blocks exposed to F. radiculosa. However, during exposure to G. trabeum copper was not translocated and remained distributed throughout the wood cell wall with concentrations of copper higher in the middle lamella (i.e., similar to unexposed control samples). This study provides new insights into the movement of copper during fungal decay of copper-treated wood.

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