Activities of cellulase and other extracellular enzymes during lignin solubilization by Streptomyces viridosporus

Abstract

Two mutant strains of the lignin degrading bacterium Streptomyces viridosporus strain T7A with enhanced abilities to produce a soluble lignin degradation intermediate, acid-precipitable polymeric lignin (APPL) and several mutants derepressed for cellulase production were compared with the wild type to examine the roles of cellulase and selected other extracellular enzymes in lignin solubilization by S. viridosporus. The two APPL-overproducing mutants, T-81 and T-138, had higher cellulase activities than the wild type. Mutants specifically derepressed for cellulase were also isolated and were found to produce more APPL than the wild type. The results are indicative of some involvement of cellulase in the lignin solubilization process. The lignin solubilized from corn (Zea mays) lignocellulose by the mutants was slightly different chemically as compared to wild type solubilized lignin in that it had a higher coumaric acid ester content. The production of extracellular coumarate ester esterase, aromatic aldehyde oxidase, and xylanase was also examined in the mutants. Xylanase and aromatic aldehyde oxidase production did not differ significantly between the mutants and the wild type. Mutant T-81 was found to have a slightly lower activity for esterase as compared with the wild type. It was concluded that xylanase, oxidase and esterase are not the enzymes directly responsible for enhanced lignin solubilization. The results, however, do implicate cellulase in the process.