Lignin biodegradation of nitrogen supplemented red oak (Quercus rubra) wood chips with two strains of Phanerochaete chrysosporium

Red oak ( Quercus rubra L.) wood chips were treated at two levels of nitrogen content (0.95% and 2.87% N level based on oven-dry wood chips) with either anhydrous liquid ammonia or ammonium nitrate in attempts to enhance the lignin degradation rate of a wild and mutant strain of Phanerochaete chrysosporium. As growth time increased, significant changes in weight loss, alkali solubility, alcohol/benzene extractive content, holocellulose content, and klason lignin content were observed. Experimental results showed that lignin biodegradation rate of both a wild and a mutant strain of P. chrysosporium was increased by pretreating the wood chips with either liquid ammonia at low levels (0.95% N) or by treating wood chips with additions of ammonium nitrate at the 0.95% N and 2.87% N level. Treating red oak chips with liquid ammonia at the 2.87% N level not only caused a reduction in holocellulose content of red oak wood chips, but also inhibited the growth of both strains of P. chrysosporium during incubation. When ammonium nitrate was added to the red oak wood chips at the 2.97% N level, biodegradation capabilities of the wild strain were suppressed. However, the red oak wood chips treated to the 2.87% N level with ammonium nitrate did not affect the growth of the mutant strain of P. chrysosporium. An increase in lignolytic activity was found to occur using the mutant strain of fungus. Significant differences in lignin and carbohydrate content of fungus-degraded wood were observed. The wild strain appeared to attack the lignin and carbohydrate constituents of wood simultaneously, resulting in a loss in both components as incubation time increased from 0 to 30 days. However, the mutant strain appeared to attack the lignin constituents while leaving the carbohydrate components largely intact. Comparison between the two strains (30 days of incubation) showed the red oak wood chips degraded by the mutant strain had a higher holocellulose content than did the wood chips degraded by the wild strain. These results suggest that the mutant strain may be the preferred fungus to use in manufacturing biomechanical pulps and the biodegradation rate may be slightly increased with the addition of nitrogen to the substrate.