Sacchariiication of Straw by Actinomycete Enzymes

Over 200 strains of actinomycetes, representing nine distinct genera, were screened directly for the ability to release reducing sugar from ball-milled wheat straw, using a microtitre plate assay system. Xylanase activity was detected in nearly all of the strains examined while activities against purified cellulosic substrates were less widespread and relatively low. Straw saccharification resulted from cooperative enzyme action and sugar yields were not simply correlated with substrate particle size. Straw-saccharifying activity was further characterized in selected strains comprising five representatives of the genera Thermomonospora and Streptomyces, one Micromonospora strain and the type strain of Microbispora bispora. Common features included optimal saccharification of straw in the pH range 64-9.0 and xylose and its oligomers as the principal products, although low concentrations of glucose were also detected. Optimal activity and increased stability at 70 "C was a feature of enzyme preparations from Thermomonospora and thermophilic Streptomyces strains. P-Xylosidase and P-glucosidase activities were largely intracellular, but significant amounts of extracellular P-xylosidase activity were also found in two strains. Other enzymes involved in straw saccharification include acetylesterase and arabinofuranosidase, and these activities were detected in all strains. Acetylesterase and arabinofuranosidase activities were largely extracellular, but in some strains significant amounts of intracellular activity were also detected.