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    Despite the drawbacks associated with tolerant organisms, copper is still used as the key component in current wood preservatives. Copper-tolerant fungi, like Fibroporia radiculosa, produce and accumulate high levels of oxalate in response to copper. The biosynthesis of oxalate has been connected to specific enzymes in the glyoxylate and tricarboxylic acid cycles. To gain insight on the mechanism of oxalate production, four F. radiculosa isolates undergoing decay of untreated and 1.2% ammoniacal copper citrate treated wood were evaluated for the differential expression of citrate synthase (CS), isocitrate lyase (ICL), glyoxylate dehydrogenase (GLOXDH), succinate/fumarate antiporter (ANTI), and a copper resistance-associated ATPase pump (ATPase). Samples were measured at 2, 4, 6, and 8 weeks and analyzed for oxalate and protein production, enzyme activities, and gene expression via RNA. ATPase pump expression was increased in the presence of copper, suggesting it functions in helping the fungus adapt to the copper-rich environment by pumping toxic copper ions out of the cell. When initial oxalate concentrations were low, ATPase expression was at its highest. As oxalate levels increased ATPase pump activity decreased, suggesting that oxalate is binding the copper and rendering it immobile. Thus, there are fewer free copper ions moving into the cell and less need for ATPase expression. These results also found a connection in expression levels between CS, ANTI, ICL, and GLOXDH for the four isolates. This suggests the production of oxalate originates in the mictochondrial TCA cycle (CS), shunts to the glyoxysomal glyoxylate cycle (ANTI), moves through a portion of the glyoxylate cycle (ICL), and ultimately is made in the cytoplasm (GLOXDH).

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    Jenkins, Katie Marie. 2012. Evaluating the Mechanism of Oxalate Synthesis of Fibroporia Radiculosa Isolates Adapting to Copper-Tolerance. A Thesis Submitted to the Faculty of Mississippi State University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Forest Products in the Department of Forest Products, 2012; 146 p.


    copper-tolerance, oxalic acid, Figroporia radiculosa

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