Carol A. Clausen

Copper tolerance of brown-rot fungi: time course of oxalic acid production

Abstract The increase in the use of non-arsenical copper-based wood preservatives in response to environmental concerns has been accompanied by interest in copper-tolerant decay fungi. Oxalic acid production by brown-rot fungi has been proposed as one mechanism of copper tolerance. Fifteen brown-rot fungi representing the genera Postia , Wolfiporia , Meruliporia , Gloeophyllum , Laetiporus , Coniophora , Antrodia , Serpula , and Tyromyces were evaluated for oxalic acid production bi-weekly in southern yellow pine (SYP) blocks treated with 1.2% ammoniacal copper citrate (CC). Eleven fungi were designated copper-tolerant based upon weight loss in CC-treated blocks. After 2 weeks, these fungi produced 2–17 times more oxalic acid in CC-treated blocks than in untreated blocks. After 10 weeks, weight loss ranged from 32% to 57% in CC-treated SYP. Four fungi were copper sensitive, producing low levels of oxalic acid and minimal weight loss in CC-treated blocks. Rapid induction of oxalic acid appeared to correlate closely with copper tolerance. We conclude that the brown-rot fungi tested that were able to exceed and maintain an oxalic acid concentration of ⩾600 μmol / g effectively decayed SYP treated with CC.

Oxalic acid overproduction by copper-tolerant brown-rot basidiomycetes on southern yellow pine treated with copper-based preservatives ☆ ☆☆

Accumulation of oxalic acid (OA) by brown-rot fungi and precipitation of copper oxalate crystals in wood decayed by copper-tolerant decay fungi has implicated OA in the mechanism of copper tolerance. Understanding the role of OA in copper tolerance is important due to an increasing reliance on copper-based wood preservatives. In this study, four copper-tolerant brown-rot fungi were evaluated for decay capacity and OA production in early stages of exposure to four waterborne copper-based wood preservatives (ammonical copper quat type B and D, ammonical copper citrate, and chromated copper arsenate, type C) and one oilborne copper-based wood preservative (oxine copper) in southern yellow pine blocks. Weight losses were less than 14% during the 4-week incubation. The presence of copper in waterborne preservatives uniformly stimulated OA production by the test fungi within 2 weeks of exposure of the treated blocks to test fungi; 66% to 93% more OA was produced in treated blocks than untreated controls. Oxine copper, a nickel-containing oilborne preservative, prevented both weight loss and OA production in all fungi tested.

Correlation between oxalic acid production and copper tolerance in Wolfiporia cocos

The increased interest in copper-based wood preservatives has hastened the need for understanding why some fungi are able to attack copper-treated wood. Due in part to accumulation of oxalic acid by brown-rot fungi and visualization of copper oxalate crystals in wood decayed by known copper-tolerant decay fungi, oxalic acid has been implicated in copper tolerance by the formation of copper oxalate crystals. Nineteen isolates of the brown-rot fungus Wolfiporia cocos were evaluated for oxalic acid production and weight loss on wood treated with 1.2% copper citrate. Twelve of 19 isolates that caused moderate to high weight losses in copper citrate-treated wood produced low oxalic acid in liquid culture, whereas isolates with high oxalic acid production had low weight losses in treated wood. Seven W. cocos isolates demonstrated enhanced weight loss in Cu-treated wood. Wood weight loss was unaffected by the presence of copper citrate for two W. cocos isolates and weight loss was lower for 10 isolates compared to weight losses in untreated wood. Citrate did not significantly influence oxalic acid production in liquid culture. Previous hypotheses linking oxalic acid and copper tolerance were based upon observations of single isolates of Postia and Tyromyces. Although most isolates produced more oxalic acid in copper citrate-treated wood than in untreated wood, we found no statistical relationship between the amount of oxalic acid production in liquid culture or wood and copper tolerance in W. cocos. Production of oxalic acid does not seem to be the factor controlling copper tolerance in W. cocos. The diversity seen within W. cocos demonstrates that caution should be used when reporting results, so that generalizations are not based on the behavior of a single isolate.

Preservation Treatment for Wood Bridge Application

Timber can often be a cost-effective construction material for new bridges. The durability of the bridge greatly depends on proper attention to construction details and fabrication, as well as proper preservative treatment before, during, and after construction. Material repair and replacement costs for bridges are a considerable expense for highway agencies. To address these needs, the objectives of an investigation were to determine the field effectiveness of various treatment alternatives used on Iowa roadway projects and to provide information on preservative treatments, inspection techniques, and current specifications for bridge owners. Special emphasis was placed on providing up-to-date synthesized information for county engineers to maintain their timber bridge inventory more effectively. The project scope included a literature review, identification of testing techniques, on-site inspections of bridges in Iowa, and a review of current specifications and testing procedures. On the basis of information evaluated, these general conclusions were made: copper naphthenate was recommended as the plant-applied preservative treatment for timber bridges, American Wood Protection Association Standards and Best Management Practices should be followed to ensure high-quality treatment of timber materials, and bridge maintenance programs would be enhanced by the development of an effective construction and remedial treatment process to improve bridge durability.

Production of antibodies to fungal endoglucanase in murine ascitic fluid

Polyclonal antibodies to endoglucanase of the brown-rot fungus Postia placenta were produced in murine ascitic fluid. The mice produced a mean volume of 17.7 mL ascites and a mean reciprocal antibody titer of 419 by ELISA. Anti-endoglucanase antibody inhibited 100 percent of the endoglucanase activity extracted from P. placenta-decayed wood.