The effects of various nutrients on extracellular peroxidases and acid-precipitable polymeric lignin production byStreptomyces chromofuscus A2 andS. viridosporus T7A

Abstract

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 ssp. appear extracellularly primarily after cells cease growing 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.