Adaptation of Ruminococcus flavefaciens resulting in increased degradationof ryegrass cell walls

This study investigated the long term adaptation of a ruminal bacterium to growth on four different plant cell wall substrates. No significant increas e in degradation was detected for lucerne. barley straw or weeping lovegras s after 23 serial subcultures of the cellulolytic rumen bacterium Ruminococ cus flavefaciens strain 17 on each of these substrates. Significantly incre ased substrate degradation by R. flavefaciens strain 17 was however observe d after 23 subcultures oil perennial ryegrass. The increase in dry matter s olubilisation (from 24.3 to 39.5% in 24 h incubation and from 52.3 to 61% i n 72 h uas at least partially due to an increase in solubilisation of xylos e, glucose and arabinose. Enhanced growth of the adapted strains occurred o n this substrate. Significant increases in xylanase and beta -xylosidase sp ecific activities were detected but no effect was detected on xylanase prof iles in zymogram analyses. Similar responses were observed for two cultures originally derived from single-colony re-isolates. The most likely explana tion for the observed adaptation involves selection for mutations affecting the regulation of xylanolytic enzymes. (C) 2001 Federation of European Mic robiological Societies. Published by Elsevier Science B.V. All rights reser ved.