The implications of the loss and regain of cotton‐degrading activity for the degradation of straw byRuminococcus flavefaciensstrain 007

摘要

Cultivation of the cellulolytic anaerobeRuminococcus flavefaciensstrain 007 on a nutrient medium containing cellobiose as energy source resulted in a four‐ to five‐fold reduction in the cotton‐degrading activity of the strain after 15–18 subcultures. Two single colony re‐isolations also lost cotton‐degrading activity after repeated cultivation on cellobiose. When the form with poor cotton‐degrading activity (007S) was serially subcultured on cotton fibres, high cotton‐degrading activity was recovered after 7–13 subcultures. One (of three) single colony re‐isolations of 007S also recovered cotton‐degrading activity under these conditions. The time course of these changes in activity suggests that they resulted from mutations. The cotton degrader (007C) was slightly more active against Avicel, Sigmacell and filter paper than was 007S, but 007S and 007C showed similar activity against acid‐swollen cellulose. Strain 007C was not significantly more active than 007S in degrading barley straw (with or without ammonia treatment) or wheat straw. The property that enables strain 007C to degrade cotton appears to play at most a minor role in the degradation of straw.