Cellulolytic actinomycetes were isolated from the hindgut of four different termites: Macrotermes, Armitermes, Odontotermes and Microcerotermes spp. The isolated actinomycetes (Streptomyces sp. and Micromonospora sp.) were grown on cellulosic substrates and their extracellular cellulase (Cl, Cx and cellobiase) activity evaluated; using filter paper as a substrate for Cl, carboxymethylcellulose (CMC) for Cx and d‐cellobiose for cellobiase, all strains were shown to degrade soluble and insoluble cellulose; optimum pH for growth was 6.2–6.7 at 28°C; three strains could grow at 48°C on cellulosic substrates. Some strains exhibited high cellulase activity, constant for 5–7 days, but inhibition by glucose was a common feature for almost all isolates.
The lignocellulose-degrading abilities of 11 novel actinomycete strains isolated from termite gut were determined and compared with that of the well-characterized actinomycete, Streptomyces viridosporus T7A. Lignocellulose bioconversion was followed by (i) monitoring the degradation of [14C]ligninand [14C]celluloselabeled phloem of Abies concolor to '4Co2 and 14C-labeled water-soluble products, (ii) determining lignocellulose, lignin, and carbohydrate losses resulting from growth on a lignocellulose substrate prepared from corn stalks (Zea mays), and (iii) quantifying production of a water-soluble lignin degradation intermediate (acid-precipitable polymeric lignin). The actinomycetes were all Streptomyces strains and could be placed into three groups, including a group of five strains that appear superior to S. viridosporus T7A in lignocellulosedegrading ability, three strains of approximately equal ability, and three strains of lesser ability. Strain A2 was clearly the superior and most effective lignoceilulose decomposer of those tested. Of the assays used, total lignocellulose weight loss was most useful in determining overall bioconversion ability but not in identifying the best lignin-solubilizing strains. A screening procedure based on '4Co2 evolution from [14C-lignin]lignocellulose combined with measurement of acid-precipitable polymeric lignin yield was the most effective in identifying lignin-solubilizing strains. For the termite gut strains, the pH of the medium showed no increase after 3 weeks of growth on lignocellulose. This is markedly different from the pattern observed with S. viridosporus T7A, which raises the medium pH considerably. Production of extracellular peroxidases by the 11 strains and S. viridosporus T7A was followed for 5 days in liquid cultures. On the basis of an increase of specific peroxidase activity in the presence of lignocellulose in the medium, the actinomycetes could be placed into the same three groups.
Fourteen Streptomyces strains known to degrade lignocellulose were screened for their ability to decolorize three anthron-type dyes: Remazol Brilliant Blue R (RBBR), blue poly(vinylamine) sulfonate – anthraquinone dye (Poly B-411), and red poly(vinylamine) sulfonate – anthrapyridone dye (Poly R-478). The relationships between efficiency of dye decolorization and capacity to attack lignocellulose were examined. Good correlation was found between lignocellulose weight losses observed during previous solid-state fermentation assays and the ability to decolorize RBBR and Poly B-411. A poor correlation was observed between Poly R-478 decolorizing activity and lignocellulose-degrading ability. The presence of corn stover lignocellulose in the culture broth enhanced decolorization of the dye by all but one of the strains. The enhancement was thought to involve the increased production of extracellular peroxidases by cultures growing on lignocellulose. The results on oxidation of the three dyes by a commercial horseradish peroxidase indicate that RBBR and Poly B-411 are suitable substrates for analyzing production of peroxidases by Streptomyces spp., while no decolorization of Poly R-478 was observed under the conditions used. However, Poly R-478 decolorizing activity of the Streptomyces may reflect the activity of other enzymes involved in the complex process of lignocellulose degradation. Key words: Streptomyces, lignocellulose, degradation, dye, decolorization.
The relationships between growth, medium pH, assimilation of glucose and amino acids, presence or absence of lignocellulose in the medium, lignin solubilization, and the appearance of extracellular peroxidase activity were compared for two lignin-solubilizing actinomycetes, Streptomyces chromofuscus A2 and S. viridosporus T7A. In a mineral salt medium containing yeast extract and three amino acids S. chromofuscus A2 grew faster than S. viridosporus T7A. When D-glucose was added to this medium, it was used in preference to the amino acids, the assimilation of which was delayed. Extracellular peroxidase activity peaked during the stationary phase, and glucose supplementation delayed peroxidase production. The eventual peak in peroxidase activity was higher in glucose-containing medium than in medium without glucose. Supplementation of the medium with lignocellulose did not affect either the level or time of appearance of extracellular peroxidase. However, lignin solubilization in lignocellulose-supplemented medium correlated positively with peroxidase activity: both increased after the cells entered the stationary phase. Supplementation of lignocellulose-containing medium with glucose delayed peroxidase production and lignin solubilization until the glucose had been assimilated, With S. viridosporus T7A, addition of D-glucose to the standard medium affected amino acid assimilation differently from S. chromofuscus A2. Glucose was consumed concomitantly with the amino acids. In the medium supplemented with lignocellulose, peroxidase activity and lignin solubilization correlated as they did for S. chromofuscus A2. A correlation of unknown significance was observed between the peroxidase activities of both strains and increasing medium pH. S. chromofuscus A2 produced more peroxidase and solubilized more lignin from lignocellulose than did S. viridosporus T7A. Overall, these findings show that extracellular peroxidases of both Streptomyces spp. apPear extracellularly primarily after cells cease growing *Paper No. 90518 of the Idaho Agricultural Experiment Station Offprint requests to: D. L. Crawford and nutrients have been depleted from the medium. Also, increasing extracellular peroxidase activity and rates of lignin solubilization in both organisms are correlated and subject to glucose repression. These results point to the involvement of stationary-phase active peroxidases in the Streptomyces-catalyzed solubilization of lignin.
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