Six biodegradative actinomycete strains were grown on a dimeric model lignin compound of the p-aryl ether type. Although only two strains, Thermomonosporu mesophifu and Sfreptomyces b d u s , utilized the compound as a carbon and energy source and produced substantial amounts of monomeric products, all of the strains could demethylate the substrate and oxidize Ca on the phenylpropane side-chain. Sfrepfomyces sp. EC1 produced small amounts of aromatic acids and unidentified lignin-derived products when grown on straw. This organism also produced cell-bound demethylase requiring H202 and Mn2+, protocatechuate 3,4-dioxygenase and pcarboxymuconate decarboxylase activity in response to growth on low-molecular-mass aromatic compounds but not lignocellulose or its polysaccharide components. Extracellular peroxidase and catalase activity were detected in all of the strains. These data are used to propose a scheme by which actinomycete attack of the lignin component of plant biomass can be envisaged.

A Streptomyces sp. isolated from compost degraded the hemicellulose fraction of straw efficiently but apparently not native cellulose. Ball-milled straw induced endoglucanase, beta-glucosidase, beta-xylanase and beta-xylosidase. Carboxymethylcellulose, cellotetraose and cellotriose induced cellulolytic enzymes specifically whereas cellobiose acted as inducer for beta-glucosidase only. Cellotriose and cellotetraose induced beta-glucosidase, but only partially induced endoglucanase. Hemicellulose (in the form of xylan) and xylobiose induced only beta-xylanase and beta-xylosidase. Kraft lignin and syringic acid induced beta-xylanase and endoglucanase but not the other enzymes. 3,4-Dimethoxycinnamic acid slightly induced beta-xylanase whereas 3,5-dimethoxy-4-hydroxycinnamic acid specifically induced endoglucanase. Neither veratric acid nor vanillic and ferulic acids induced any of the cellulolytic or hemicellulolytic enzymes. Enzyme production was subject to a form of carbon catabolite repression. Endoglucanase and beta-xylanase were excreted into the culture medium. Four protein components, one acidic (pI 5.2) and three basic (pI 8.15, 8.45 and 8.65) exhibited beta-xylanase activity. Two acidic components (pI 3.55 and 3.75) displayed endoglucanase activity.

Actinomycetes grown on wheat straw solubilized a lignocarbohydrate fraction which could be recovered by acid precipitation. Further characterization of this product (APPL) during growth of Streptomyces sp. strain EC1 revealed an increase in carboxylic acid and phenolic hydroxyl content, suggesting progressive modification. This was also observed in dioxane-extracted lignin fractions of degraded straw, and some similarity was further suggested by comparative infrared spectroscopy. However, the molecular weight profile of APPL was relatively constant during growth of Streptomyces sp. strain EC1 on straw, while analysis of the dioxaneextracted lignin fractions appeared to show fragmentation followed by repolymerization. Lignocarbohydrate solubilization could be monitored in all cultures by routine assay of APPL-associated protein, which accounted for up to 20% of the extracellular culture protein in some cases. Interestingly, this protein fraction was found to include active hydrolytic and oxidative enzymes involved in the degradation of lignocellulose, and specific enzyme activities were often increased in the acid-insoluble fractions of culture supernatants. This was particularly important for peroxidase and veratryl oxidase activities, which could be readily detected in the acid-precipitable lignocarbohydrate complex but were virtually undetectable in untreated culture supernatants.

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