Gene expression of selected decay enzymes produced during biodeterioration of three wood types
IRG/WP 09-10702
Young-Min Kang, L Prewitt, S Diehl
Comparative studies were conducted on the expression of several decay enzyme genes during the decay of pine, cedar, and ACQ treated pine over 10 months. Measurements of MOE, decay rating, and moisture control were monitored for physical properties. Identification of decay fungi and the detection of decay enzymes were carried out before gene expression levels were measured. The MOE of wood stakes decreased more in pine than in cedar and ACQ treated pine, indicating a greater loss of strength. Visual decay rating data paralleled MOE data at each sampling time. Moisture contents of all three wood types in each container varied between 40% and 100% over the 10 months. Basidiomycetes were found on all samples as determined by PCR amplification of the basidiomycete 18s rRNA gene after 4 months. For identification of decay fungi at 4 months, PCR products of basidiomycete 18s rRNA gene were cloned and sequenced. Four species of basidiomycetes on cedar, six on ACQ treated pine, and twelve on pine were identified. The white rot fungus, Phlebia radiata was identified on all wood stakes. P. radiata species specific primers were then designed to track the expression of three decay enzyme genes: lignin peroxidase (Lip), manganese peroxidase (Mnp), and laccase (Lcc) on wood samples. Gene expression data as measured by Real-time PCR indicated that the Mnp expression level on pine at 4 months was very similar to the expression level on ACQ-pine but was not detected on cedar. The Lcc expression level on pine samples at 6 months was 30% less than the expression level on ACQ-treated pine while no Lcc was detected on cedar. The results clearly show that the naturally durable properties of cedar reduce the wood decay community and its activities in comparison to untreated pine and ACQ-treated pine. P.radiata attempted to decay the ACQ-treated wood by producing a large amount of Lcc than was produced on pine but the MOE data showed this attack was not successful. Thus, it appears ACQ-treated wood does not stop the production of the decay enzymes but does inhibit the effectiveness of the enzymes. Results from the study indicate that different resistant woods have different effects on the microbial communities and its enzymatic activities during decay.