Influence of lignin peroxidase concentration and localisation in lignin biodegradation by Phanerochaete chrysosporium

Formation pathway of disinfection by-products of lignin monomers in raw water during disinfection

In this study, the dissolved organic matter (DOM) profiles of water samples from a water source in northeastern China were analyzed by high-resolution mass spectrometry (HRMS), and its changes after chlorination were investigated. The results showed that lignin substances accounted for a significant proportion in DOM and chlorinated products and were the main precursors of disinfection by-products (DBPs). During disinfection, macromolecular DOM was transformed into small molecules, and lignin substances have the most obvious and complex changes in reaction. Two lignin monomers 4-propylphenol (4PP) and 4-propylguaiacol (4PG) were used as model compounds to study their reaction kinetics and degradation pathways during disinfection. The degradation of both lignin monomers conformed to pseudo-first-order reaction kinetics, and the reaction rate constant of 4PG was higher than that of 4PP. The effects of chlorine dosage, pH and temperature on the degradation reaction kinetics of two lignin monomers were investigated. The degradation rates of 4PP and 4PG increased with increasing chlorine dosage, pH and temperature. The two monomers showed similar properties in the chlorination degradation process, and generated multiple intermediates, which were mainly transformed into small molecules by chlorine electrophilic substitution and nucleophilic substitution, and further generated DBPs.

Heterogeneity and regulation of manganese peroxidases from Phanerochaete chrysosporium

Lignin and Mn peroxidases are two families of isozymes produced by the lignin-degrading fungus Phanerochaete chrysosporium under nutrient nitrogen or carbon limitation. We purified to homogeneity the three major Mn peroxidase isozymes, H3 (pI = 4.9), H4 (pI = 4.5), and H5 (pI = 4.2). Amino-terminal sequencing of these isozymes demonstrates that they are encoded by different genes. We also analyzed the regulation of these isozymes in carbon- and nitrogen-limited cultures and found not only that the lignin and Mn peroxidases are differentially regulated but also that differential regulation occurs within the Mn peroxidase isozyme family. The isozyme profile and the time at which each isozyme appears in secondary metabolism differ in both nitrogen- and carbon-limited cultures. Each isozyme also responded differently to the addition of a putative inducer, divalent Mn. The stability of the Mn peroxidases in carbon- and nitrogen-limited cultures was also characterized after cycloheximide addition. The Mn peroxidases are more stable in carbon-limited cultures than in nitrogen-limited cultures. They are also more stable than the lignin peroxidases. These data collectively suggest that the Mn peroxidase isozymes serve different functions in lignin biodegradation.

Intermediates and products of synthetic lignin (dehydrogenative polymerizate) degradation by Phlebia tremellosa

Agitated, nitrogen-limited cultures of Phlebia tremellosa caused substantial changes in the distribution of 14C-labelled synthetic lignin (dehydrogenative polymerizate [DHP]) between water-soluble, dioxane-soluble, alkali-soluble, and insoluble fractions before much lignin carbon was metabolized to CO2. First, the insoluble form increased at the expense of the dioxane-soluble form. Later, the amounts of alkali-soluble and water-soluble 14C increased, and release of 14CO2 began. The molecular weight distribution of the dioxane-soluble lignin remained constant during degradation, but that of the water-soluble fraction changed to higher molecular weights. Culture agitation accelerated the attachment of suspended DHP to the mycelia and stimulated production of water-soluble 14C and 14CO2. The nonionic detergent Tween 80 also hastened release of 14CO2 and increased the early conversion of dioxane-soluble DHP to the alkali-soluble and insoluble forms. Oxidative polymerization is suggested as the first step in degradation of DHP by P. tremellosa.