Biodegradation of a Biocide (Cu-N-Cyclohexyldiazenium Dioxide) Component of a Wood Preservative by a Defined Soil Bacterial Community

The wood protection industry has refined their products from chrome-, copper-, and arsenate-based wood preservatives toward solely copper-based preservatives in combination with organic biocides. One of these is Cu-HDO, containing the chelation product of copper and N-cyclohexyldiazenium dioxide (HDO). In this study, the fate of isotope-labeled (¹³C) and nonlabeled (¹²C) Cu-HDO incorporated in wood sawdust mixed with soil was investigated. HDO concentration was monitored by high-pressure liquid chromatography. The total carbon and the δ¹³C content of respired CO₂, as well as of the soil-wood-sawdust mixture, were determined with an elemental analyzer-isotopic ratio mass spectrometer. The concentration of HDO decreased significantly after 105 days of incubation, and after 24 days the ¹³CO₂ concentration respired from soil increased steadily to a maximum after 64 days of incubation. Phospholipid fatty acid-stable isotope probing (PFA-SIP) analysis revealed that the dominant PFAs C₁₉:₀d8,9, C₁₈:₀, C₁₈:₁ω7, C₁₈:₂ω6,9, C₁₇:₁d7,8, C₁₆:₀, and C₁₆:₁ω7 were highly enriched in their δ¹³C content. Moreover, RNA-SIP identified members of the phylum Acidobacteria and the genera Phenylobacterium and Comamonas that were assimilating carbon from HDO exclusively. Cu-HDO as part of a wood preservative effectively decreased fungal wood decay and overall microbial respiration from soil. In turn, a defined bacterial community was stimulated that was able to metabolize HDO completely.