A chimeric enzyme associating feruloyl esterase A (FAEA) from Aspergillus niger and dockerin from Clostridium thermocellum was produced in A. niger. A completely truncated form was produced when the dockerin domain was located downstream of the FAEA (FAEA-Doc), whereas no chimeric protein was produced when the bacterial dockerin domain was located upstream of the FAEA (Doc-FAEA). Northern blot analysis showed similar transcript levels for the two constructs, indicating a posttranscriptional bottleneck for Doc-FAEA production. The sequence encoding the first 514 amino acids from A. niger glucoamylase and a dibasic proteolytic processing site (kex-2) were fused upstream of the Doc-FAEA sequence. By using this fusion strategy, the esterase activity found in the extracellular medium was 20-fold-higher than that of the wild-type reference strain, and the production yield was estimated to be about 100 mg of chimeric protein/liter. Intracellular and extracellular production was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, dockerin-cohesin interaction assays, and Western blotting. Labeled cohesins detected an intact extracellular Doc-FAEA of about 43 kDa and a cleaved-off dockerin domain of about 8 kDa. In addition, an intracellular 120-kDa protein was recognized by using labeled cohesins and antibodies raised against FAEA. This protein corresponded to the unprocessed Doc-FAEA form fused to glucoamylase. In conclusion, these results indicated that translational fusion to glucoamylase improved the secretion efficiency of a chimeric Doc-FAEA protein and allowed production of the first functional fungal enzyme joined to a bacterial dockerin.Plant cell walls are composed of various polysaccharides and lignin, forming a rigid and complex matrix recalcitrant to microbial degradation. This structure is strengthened by crosslinkages such as diferulic acid bridges between adjacent hemicellulose chains (28) or between lignin and hemicellulose (24), increasing its resistance to microbial invasion. Aerobic and anaerobic microorganisms have developed two main efficient mechanisms of plant cell wall degradation. In the first system, microorganisms secrete free extracellular enzymes in contact with a substrate. The products of degradation constitute both nutrients for growth and regulators of the production of lignocellulolytic enzymes (9, 42, 43). Among these microorganisms, filamentous fungi such as Trichoderma spp. and Aspergillus spp. are especially good secretors of lignocellulolytic enzymes (1). Moreover, Aspergillus niger produces enzymes named feruloyl esterases (EC 3.1.1.73), a subclass of the carboxylic ester hydrolases, that are able to hydrolyze diferulate cross-links in plant cell walls, facilitating the access of main-chain-degrading enzymes to the polysaccharide backbone (8,46). Furthermore, feruloyl esterases release cross-linked aromatic acids, such as ferulic acid, which is an attractive industrial compound by virtue of its antioxidant, photoprotectant properties (18) and its potential biotr...