Monday, April 30, 2007 - 10:10 AM

Penicillium brasilianum as an enzyme factory for the hydrolysis of the plant cell wall: the essential role of feruloyl esterases

Gianni Panagiotou and Lisbeth Olsson. BioCentrum-DTU, Technical University of Denmark, Building 223, Lyngby, Denmark

The regulation of the production of arabinoxylan-degrading enzymes produced by the fungus Penicillium brasilianum was investigated. An investigation of the relation between the composition of the carbon source and the level of enzymes produced revealed that  higher feruloyl esterase (225 mU/ml) and α-L-arabinofuranosidase (211 mU/ml) activities were obtained when P. brasilianum was grown on sugar beet pulp, that was the carbon source with the highest content of ferulic acid. In contrast, the maximum xylanase (17 U/ml) was found during growth on oat spelt xylan {Poly(β-D-xylopyranose[1->4]),  that contains 10% arabinose, 15% glucose residues and <0.0007% ferulic acid}. The production of the enzymes was further stimulated by the presence of free ferulic acid pointing to that the fungal regulatory mechanism involved in the production and secretion of feruloyl esterase, xylanase and α-L-arabinofuranosidase could be coordinated in P. brasilianum.

The specificity profile of P. brasilianum crude extract against the hydroxycinnamic acid methyl esters suggests that it contains only type-B feruloyl esterases. Since agroindustrial by-products are a potential source of added-value phenolic acids with promising applications in the food and pharmaceutical industries crude enzyme mixtures of P. brasilianum were tested for their hydrolysis abilities against 8 complex and commercial purified substrates. While total release of phenolic acids and pentoses was not observed, the synergistic enhancement of hydrolysis in the present of feruloyl esterase was clearly demonstrated.