Sacchariiication of Straw by Actinomycete Enzymes

Abstract

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.

Towards elucidation of the lignin degradation pathway in actinomycetes

“…Actinomycete strains (Table 1) were maintained as spore suspensions and hyphal fragments in 20% (v/v) glycerol at -70 "C, and routinely cultured on L-agar (Hopwood el al., 1985). Distilled-water suspensions of sporulating growth were used to inoculate shake flasks containing basal salts medium supplemented with ball-milled wheat straw (Ball & McCarthy, 1988). Conical flasks (250 ml) containing 50 ml growth medium were used throughout.…”

Is the solubilized product from the degradation of lignocellulose by actinomycetes a precursor of humic substances?

“…Their hyphal growth is well suited for the colonization of plant biomass and they secrete a range of enzymes active against lignocellulose (McCarthy & Ball, 1991). Research on the biodegradation of lignin by actinomycetes has focused on the screening and detection of good lignocellulose degraders (Crawford, 1978;Crawford e t al., 1983;McCarthy & Broda, 1984;Ball & McCarthy, 1988;Ball et al, 1989;Trigo & Ball, 1994 , 1984). This difference in lignin degradation rates between fungi and bacteria is probably due to different strategies of lignin degradation developed by these two groups of micro-organisms.…”

Extracellular Heme Peroxidases in Actinomycetes: a Case of Mistaken Identity

“…Some actinomycetes, including thermophilic species and streptomycetes, secrete cellulose-and hemicellulose-degrading enzymes (2,4,11). Since the discovery of extracellular lignindegrading heme peroxidases of wood-rotting fungi, considerable effort has been expended in searching for analogous enzymes in the cellulolytic actinomycetes (9,22,24).…”