INFLUENCE OF FERULIC ACID ON THE PRODUCTION OF FERULOYL ESTERASES BY ASPERGILLUS-NIGER

Extracellular feruloyl esterases from the filamentous fungus Aspergill us niger are induced by growth on oat spelt xylan (OSX), which contain s no detectable esterified ferulic acid. FAE-III accounted for most of the feruloyl esterase activity. Addition of free ferulic acid to OSX at the start of the culture induced FAE-III secretion a further 2.3-fo ld, and also induced other feruloyl esterases which could not be ascri bed to FAE-III. Wheat bran-(WB)-grown cultures, containing 1% (m/v) es ter-linked ferulic acid, gave almost identical FAE-III and total ferul oyl esterase activities as the cultures grown on OSX plus ferulic acid . De-esterification of WB yielded less total feruloyl esterase, and 2. 4-fold less-FAE-III, compared to untreated WB. A slightly modified for m of FAE-III was produced on de-esterified WB. These results show that production of FAE-III does not absolutely require ferulic acid. Howev er, production is stimulated by the presence of free ferulic acid thro ugh increased expression; and is reduced by the removal of esterified ferulic acid from the growth substrate.