Expression of a modified Neocallimastix patriciarum xylanase in Butyrivibrio fibrisolvens digests more fibre but cannot effectively compete with highly fibrolytic bacteria in the rumen

Aims: This study investigated the competitive abilities of two Neocallimast ix patriciarum-derived xylanases constructs in Butyrivibrio fibrisolvens H1 7c (xynA and pUMSX) and their ability to compete in vivo. Methods and Results: The digestibility of neutral detergent fibre (NDF) inc reased during co-culture of xynA or pUMSX and weakly cellulolytic, but not with highly cellulolytic, ruminococci. Competition studies among xynA, pUMS X and cellulolytic consortia demonstrated that xynA was the fittest. XynA d id not persist at high levels in the rumen and was undetectable after 22 da ys. Conclusions: The construction of recombinant xylanolytic B. fibrisolvens do es improve the digestibility of fibre above that of the native, but digesti bility is still less than that of the most potent fibre digesters such as r uminococci. Significance and Impact of the Study: Fibre digestion may be improved by ge netic manipulation of ruminal bacteria but ecological parameters, such as p ersistence in vivo and the niche of the organism, must be taken into accoun t.