No abstract

Veratryl alcohol, added as a supplement to cultures of Phanerochaete chrysosporium, enhanced ligninase activity through protection of the ligninase against inactivation by hydrogen peroxide produced by this fungus in cultures. In the presence of veratryl alcohol, the loss of ligninase activity observed in non-proteinsynthesizing cultures (cycloheximide-treated) equaled the extracellular protein turnover. When cultures were not supplemented with veratryl alcohol, inactivation of ligninase by hydrogen peroxide added to protein turnover, resulting in a more rapid loss of ligninase activity. Although all ligninase isoenzymes are sensitive to inactivation by hydrogen peroxide, only the isoenzyme of the highest specific activity (80.6 nkat mg of protein-'; Mr, 41,800; pl, 3.96) was found to be protected by veratryl alcohol. The concentration of veratryl alcohol necessary for full protection of ligninase activity varied according to the concentration of hydrogen peroxide present in the medium, which depended on the nature of the carbon source (glucose or glycerol). It is proposed that the nature of the carbon source influences the overall ligninase activity not only directly, by affecting the rate and the type of synthesized ligninase, but also by affecting the rate of hydrogen peroxide production, bringing about different rates of inactivation.

No abstract

Eleven gram-negative aerobic bacteria ( Pseudomonadaceae and Neisseriaceae ) out of 122 soil isolates were selected for their ability to assimilate poplar dioxane lignin without a cosubstrate. Dioxane lignin and milled wood lignin degradation rates ranged between 20 and 40% of initial content after 7 days in mineral medium, as determined by a loss of absorbance at 280 nm; 10 strains could degrade in situ lignin, as evidenced by the decrease of the acetyl bromide lignin content of microtome wood sections. No degradation of wood polysaccharides was detected. Lignin biodegradation by Pseudomonas 106 was confirmed by 14 CO 2 release from labeled poplar wood, although in lower yields compared with results obtained through chemical analysis based on acetyl bromide residual lignin determination.

Structural changes and resulting in-vitro dry matter digestibility (IVDMD) were determined during the course of solid-state fermentation of wheat straw using the lignin-degrading white-rot fungi Sporotrichum pulverulentum, Pycnoporus cinnabarinus and Cyathus stercoreus. The first fungus grew very rapidly on straw but degraded hemicelluloses and cellulose non-selectively resulting in very low IVDMD increases (50% after 35% weight loss). P. cinnabarinus and C. stercoreus preferentially degraded hemicelluloses achieving high improvements in IVDMD (maximum increase of 63 and 94%, respectively) with limited dry weight losses (12 and 18% after 7 and 13 days, respectively). The three fungi exhibited some selectivity among the individual hemicellulose components: 0-acetyls were removed essentially at the same rate as xylan, while uronic acids accumulated as incubation proceeded. Conversely, the arabinose content decreased rapidly, especially with C. stercoreus and P. cinnabarinus, suggesting that removal of this pentose was partly responsible for digestibility improvement. Esterified phenolic acids were rapidly degraded during the first stages of decay by all three fungi although P. cinnabarinus and C. stercoreus degraded ferulic acid faster than p-coumaric acid. Lignin was preferentially degraded compared to polysaccharides by all three fungi. The amount of lignin removed, as determined by Klason, correlated well with IVDMD improvement (r= -0.97), while acid detergent lignin (ADL) showed a lower correlation (r= -0.86). Acidolysis yields of decayed lignin pointed to preferential degradation of 8 -0 -4 ether linked units by the fungi. Syringyl units were removed faster than guaiacyl units only after 5 to 10% weight loss was obtained.