Degradation of Kraft Indulin Lignin by Streptomyces viridosporus and Streptomyces badius

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Crawford and collaborators have studied extensively the solubilization of lignocellulose by two Streptomyces species, S. badius and S. viridosporus. Using a condensed industrial lignin essentially devoid of carbohydrates, Indulin AT, as the sole source of carbon, similar results were obtained: (i) the growths of the bacteria were optimum at pH 7.5 to 8.5; (ii) yeast extract was a better source of nitrogen than NH4Cl; (iii) the products of the depolymerization of Indulin were soluble, acid-precipitable polymers. When d-glucose was added as a secondary carbon source, it was used preferentially and the production of acid-precipitable polymers began only after the complete depletion of the sugar. On the assumption that the degradation of Indulin was catalyzed by enzymes, proteins found in the culture media and soluble and insoluble intracellular proteins were incubated with Indulin at pH 7.0 at 37°C. Proteins in all fractions from S. badius had ligninolytic activities which, with the exception of those in the intracellular soluble fraction, were increased in the presence of H2O2. In S. viridosporus, both extra- and intracellular soluble activities were found which were not increased by H2O2. The extracellular activity of S. viridosporus was not affected by heat, resisted partially an exposure to pH 1.0, and was completely destroyed by proteolysis.

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