A gene (cinI) encoding a cinnamoyl ester hydrolase (CEH) has been isolated from the ruminal bacterium, Butyrivibrio fibrisolvens E14, using a model substrate, MUTMAC [4-methylumbelliferoyl (p-trimethylammonium cinnamate chloride)]. CinI has significant amino-acid similarities with members of a large and diverse family of hydrolases with a serine/aspartic acid/histidine catalytic triad. Our analyses identified two previously unclassified amino acid sequences, the amino-terminal domain of unknown function in XynZ from Clostridium thermocellum and XynC, an acetylxylan esterase from Caldicellulosiruptor saccharolyticus, as members of the same family of hydrolases. A previously described esterase with CEH activity, XylD from Pseudomonas fluorescens ssp. cellulosa, is not similar to CinI. CinI was expressed at high levels in the periplasmic fraction of E. coli TOPP2 and released ferulic acid from Fara [5-O-(trans-feruloyl)-arabinofuranose] prepared from wheat bran.

Aims: This study investigated the competitive abilities of two Neocallimastix patriciarum‐derived xylanases constructs in Butyrivibrio fibrisolvens H17c (xynA and pUMSX) and their ability to compete in vivo. Methods and Results: The digestibility of neutral detergent fibre (NDF) increased during co‐culture of xynA or pUMSX and weakly cellulolytic, but not with highly cellulolytic, ruminococci. Competition studies among xynA, pUMSX and cellulolytic consortia demonstrated that xynA was the fittest. XynA did not persist at high levels in the rumen and was undetectable after 22 days. Conclusions: The construction of recombinant xylanolytic B. fibrisolvens does improve the digestibility of fibre above that of the native, but digestibility is still less than that of the most potent fibre digesters such as ruminococci. Significance and Impact of the Study: Fibre digestion may be improved by genetic manipulation of ruminal bacteria but ecological parameters, such as persistence in vivo and the niche of the organism, must be taken into account.