The biodegradation of quaternary ammonium compounds by mould fungi

Didecyldirhethylarrmionium chloride (DDAC) has been described as one of the most effective quaternary ammonium compound (QAC) wood preservatives, based on laboratory experiments. Subsequently, QAC-treated stakes failed rapidly in field tests. It was suggested that the degradation of QACs by mould and stain fungi had reduced the efficacy of QACs. This thesis describes a study of the role that moulds play in limiting the performance of DDAC. Fungi were isolated from DDAC-treated stakelets placed in a field test site at UBC. Other fungal strains were obtained from culture collections. A comparison was made of their tolerance and ability to degrade DDAC. Experiments were performed both in solid malt agar and Vogel liquid media with, and without, DDAC. It was found that tolerance and ability to degrade DDAC shown by the fungal strains were common properties of many of the moulds studied. The metabolites produced by the action of moulds on DDAC were extracted by methylene chloride and analyzed by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The results showed that DDAC had been degraded by mould fungi, either by fission of the C-N bond or co-and (3-oxidation of the decyl group. Electrophoresis was performed to try to identify additional proteins arising from the presence of DDAC. New proteins bands were obtained in the extracellular supernatant. The DDAC concentration in liquid media was decreased when inoculated and incubated with the extracellular supernatant recovered from Verticillium bulbillosum grown in liquid media containing 250 ppm DDAC. No new proteins were obtained in the intracellular extract, and no degradation of the DDAC was recorded when the intracellular supernatant was incubated with DDAC. This suggested that DDAC degradation took place outside the fungal cell wall.Forestry, Faculty ofGraduat