Some aspects of cellobiose effect on bacterial cell surface structures involved in lucerne cell walls utilization by fresh isolates of rumen bacteria

Abstract

The effect of the inclusion of cellobiose or lucerne cell solubles on the pattern of lucerne cell walls (CW) digestion by a mixed rumen population in vitro was followed. Inclusion of soluble sugars reduced the rate of lucerne CW degradation by a mixed rumen population without reducing the extent of overall CW digestion (59.8%). The predominant ruminal bacteria utilizing lucerne hay or lucerne CW as the sole added carbohydrate substrate were isolated, enumerated and identified. Fresh isolates of the predominant cellulolytic bacteria ( Ruminococcus flavefaciens 7a3, Ruminococcus albus 7a6 and Bacteroides succinogenes 7a8 or 7a14) were then grown on lucerne CW or cellobiose as the sole added carbohydrate substrate. The effect of substrate on bacterial cell surface topology was investigated by scanning electron microscopy (SEM) visualization using cationized ferritin pretreatment and the ability of the isolates to adhere to cellulose was determined. Lucerne CW degradability by each of these bacterial isolates was also determined. The surface topology of B. succinogenes 7a14 and 7a8, R. albus 7a6 and R. flavefaciens 7a3 cells grown on and attached to CW particles was specified by a dense layer of characteristic protuberant structures. In contrast, when grown on cellobiose the surface topology of these bacterial strains (excluding isolate 7a8 of B. succinogenes) was smoother and contained less protuberant structures. The ability to attach to cellulose of these bacterial strains was higher when adapted to lucerne CW vs. cellobiose, indicating possible involvement of these organelles in the attachment mechanism of the bacteria. A possible explanation for the inhibitory effect of cellobiose on CW digestion in this study is discussed.