Breakdown of Douglas-fir phloem by a lignocellulose-degrading Streptomyces

An actinomycete, Streptomyces flavovirens, was shown to decay the intact cell walls of Douglas-fir phloem. Disks that had been cut from the inner bark were autoclaved, leached with sterile water, and inoculated with S. flavovirens. Decay produced by the actinomycete was observed by scanning electron microscopy, and the residual phloem was analyzed for weight loss and changes in carbohydrate and lignin content. After growth of S. flavovirens for 12 weeks, inoculated disks had lost 47% of the leached dry weight, whereas sterile control disks had lost only 12%. The bulk of the material degraded by the actinomycete was carbohydrate. Scanning electron micrographs of decayed phloem disks showed irregular cavities in the cell walls of parenchyma and sclereids, with actinomycete hyphae penetrating these cavities.