Isolation of lignocellulose-decomposing actinomycetes and degradation of specifically 14C-labeled lignocelluloses by six selected Streptomyces strains

Abstract

Forty-two actinomycete strains were isolated by enrichment techniques from soils and other lignocellulose-containing natural habitats. Isolates were screened for their lignocellulose-decomposing abilities using a substrate weight loss – ¹⁴C-labeled lignocellulose degradation assay which determined the relative abilities of each isolate to attack lignin versus glucan components of lignocellulose. Six Streptomyces strains were selected for further study, based upon their abilities to decompose significantly both lignin and glucan components of lignocellulose. The selected strains were examined under defined cultural conditions for their abilities to decompose ¹⁴C-labeled lignocelluloses prepared from Douglas fir. The ¹⁴C-labeled lignocellulose substrates included specifically lignin-labeled or glucan-labeled lignocelluloses, and two [¹⁴C]lignin lignocelluloses labeled specifically in only the lignin side chain or ring components. Results showed that the Streptomyces strains decomposed substantial amounts of both lignin and glucan components to ¹⁴CO₂, and ¹⁴C-labeled water-soluble products. As compared with previously described lignocellulose-degrading streptomycetes, these strains were generally more efficient decomposers of the lignin component of lignocellulose, but were similar in their abilities to decompose the glucan component. Characterization of growth on specifically labeled lignins showed that aromatic ring structures within the lignin were cleaved and a substantial percentage of the ring carbons were released as CO₂. In contrast, side-chain components were attacked to only a limited degree. These streptomycetes were similar to other recently characterized lignin-decomposing bacteria in their overall abilities to degrade lignin, but their specificity of attack on the structural components of lignin appears to be different.