Novel ferulic acid esterases are induced by growth of Aspergillus niger on sugar-beet pulp

Abstract

A ferulic acid esterase (FAE-III), which was induced by growth of Aspergillus niger CBS 120.49 on oat-spelts xylan, was capable of releasing ferulic acid from wheat bran but not from sugar-beet pulp (SBP) (Faulds CB, Williamson G (1994) Microbiology 140:779—787). Growth of this strain on SBP gave low levels of ferulic acid esterase activity (using methyl ferulate as substrate). A similar growth with a di⁄erent A. niger strain (CS 180) gave tenfold higher levels of esterase activity. Assaying culture filtrates obtained from A. niger CS 180 grown on SBP over a 3 to 10-day period against four simple phenolic methyl esters dem- onstrated that at least two esterases were produced, and, by comparison of substrate specificity, FAE-III was either absent or present only at low levels. Further- more, immunodetection of proteins did not detect the presence of FAE-III in culture supernatants of SBP- grown cultures, whereas it did in cultures grown on oat-spelts xylan. These results show that SBP does not contain the inducer for FAE-III, but does induce novel esterases. When A. niger CS 180 cultures were grown on di⁄erent carbon sources, esterase activity was in- duced on SBP, sugar-beet arabinan and oat-spelts xylan, but not on simple sugars or de-esterified sugar- beet pectin. Further, SBP-grown cultures co-inoculated with arabinanase, galactanase or xylanase did not ex- hibit increased levels of extracellular FAE activity or an earlier appearance of esterase activity, although there was an increase in esterase activity with added poly- galacturonase. These results show that novel esterases are induced by growth of A. niger on SBP.