Lignin degrading activity of Phanerochaete chrysosporium Burds.: comparison of cellulase-negative and other strains

Abstract

This study compared selected strains of Phanerochaete chrysosporium on the basis of their total ligninolytic activity ([ 14C] lignin→ 14 CO 2), and production of lignin-depolymerizing enzymes, ligninases. The seven strains included three wild-type isolates (ME-446, K-3 and BKM-F-1767), three cellulase-negative (Cel −) mutants (3113, 13132-176 and 85118-22, all derived from K-3), and one mutant strain selected for rapid decolorization of an industrial by product lignin (SC26, derived from BKM-F-1767). Grown on glucose under nitrogen-limiting conditions in a chemically defined medium, the strains varied considerably in total ligninolytic activity, in ligninase activity, in time to reach maximum ligninase activity, in amount of total extracellular protein and in relative contributions of proteins with ligninase activity. Strain SC26 produced the highest total and specific ligninase (veratryl alcohol oxidizing) activity (34 U l −1; 7.2 U mg −1 of extracellular protein). Highest total ligninolytic activity was also seen in strain SC26. In contrast, strain 13132-176 produced only negligible ligninase activity (<1 U l −1; <0.3 U mg −1 of extracellular protein), and exhibited only very low total ligninolytic activity. The other strains, including Cel - strains 85118-22 and 3113, showed much better ligninase and ligninolytic activities than 13132-176. Overall, little relation was noted between ligninase activity and total ligninolytic activity. Addition of glucose oxidase to cultures increased the rate of oxidation of lignin to CO 2 by most strains, indicating that extracellular H 2O 2, which is required by ligninase, is often rate-limiting. All seven strains contained a homologous ligninase protein, seen by gel electrophoresis and Western blot analysis using rabbit anti-ligninase prepared from BKM-F-1767. Results reveal wide variation in lignin-degrading capacity of P. chrysosporium and show that Cel - mutants can be unaffected in lignin-degrading ability.