The enzymatic hydrolysis of plant fiber by cellulases and hemicellulases can be enhanced by the presence
of ferulic acid esterase (FAE) and acetylxylan esterase (AE) activity. FAE (EC 3.1.1.73) catalyzes the
hydrolysis of ferulic acid sugar esters, thereby modifying digestion-limiting lignin-polysaccharide or
polysaccharide-polysaccharide cross-linkages in plant cell walls. AE (EC 3.1.1.72) hydrolyzes acetyl
groups from acetylated polysaccharides, thus increasing accessibility to other hydrolytic enzymes. These
accessory enzymes are of considerable importance due to their roles in many agricultural and
biotechnological processes. Lactobacillus buchneri strain PTA-6138 has been found to hydrolyze the
synthetic substrates 4-nitrophenyl ferulate and 4-nitrophenyl acetate, while its specificity for natural
substrates is unknown. Treating forage at ensiling with additives containing this strain resulted in an
increased extent of ruminal degradation of perennial ryegrass silage and whole plant corn silage in recent in
situ studies (Nsereko, et al., Anim. Feed Sci. Technol. (2007) In press). In order to characterize the
enzymes responsible for these observations, a size-fractionated Sau3AI digested total DNA library was
constructed in the vector pUC18 and screened for FAE activity clearing of agar media containing ethyl 4hydroxy-3-methoxycinnamate. DNA sequence analysis of a three kilobase positive clone identified two
ORFs encoding proteins with significant homology to esterases. Each ORF was amplified by PCR and
expressed in E. coli BL21-Gold (DE3) cells using a modified Gateway® pET28 vector. Histidine-tagged
fusion proteins were purified and characterized. Both proteins were found to hydrolyze 4-nitrophenyl
ferulate and 4-nitrophenyl acetate. Selected Lactobacillus buchneri strains have been extensively utilized
for silage preservation due to their unique aerobic stability-enhancing characteristics. A strain with FAE
activity has the potential to contribute significantly to the nutritive value of silage.