NOVEL FERULIC ACID ESTERASES ARE INDUCED BY GROWTH OF ASPERGILLUS-NIGER ON SUGAR-BEET PULP

A ferulic acid esterase (FAE-III), which was induced by growth of Aspe rgillus niger CBS 120.49 on oat-spelts xylan, was capable of releasing ferulic acid from wheat bran but not from sugar-beet pulp (SBP) [Faul ds CB, Williamson G (1994) Microbiology 140:779-787]. Growth of this s train on SBP gave low levels of ferulic acid esterase activity (using methyl ferulate as substrate). A similar growth with a different A. ni ger strain (CS 180) gave tenfold higher levels of esterase activity. A ssaying culture filtrates obtained from A. niger CS 180 grown on SBP o ver a 3 to 10-day period against four simple phenolic methyl esters de monstrated that at least two esterases were produced, and, by comparis on of substrate specificity. FAE-III was either absent or present only at low levels. Furthermore, immunodetection of proteins did not detec t the presence of FAE-III in culture supernatants of SBP-grown culture s, whereas it did ill cultures grown on oat-spelts xylan. These result s show that SBP does not contain the inducer for FAE-III, but does ind uce novel esterases. When A. niger CS 180 cultures were grown on diffe rent carbon sources, esterase activity was induced on SBP, sugar-beet arabinan and oat-spelts xylan, but not on simple sugars or de-esterifi ed sugarbeet pectin. Further, SBP-grown cultures co-inoculated with ar abinanase, galactanase or xylanase did not exhibit increased levels of extracellular FAE activity or an earlier appearance of esterase activ ity, although there was an increase in esterase activity with added po lygalacturonase. These results show that novel esterases are induced b y growth of A. niger on SBP.