Monday, May 4, 2009
5-57
Hemicellulolytic enzymes from the maize endophyte Acremonium zeae
Kenneth M. Bischoff1, Douglas B. Jordan2, Sebastiao T. de Rezende3, and Joseph O. Rich1. (1) Bioproducts and Biocatalysis Research Unit, USDA-ARS-NCAUR, 1815 N. University St., Peoria, IL 61604, (2) Fermentation Biotechnology Research Unit, USDA-ARS-NCAUR, 1815 N. University St., Peoria, IL 61604, (3) Universidade Federal de Vicosa, 36570-000 Vicosa, Minas Gerais, Brazil
A complex suite of enzymatic activities is required for complete hydrolysis of the hemicellulose fraction of lignocellulosic biomass. Acremonium zeae is one of the most prevalent fungal colonists of preharvest maize, producing symptomless infections of seeds and inhabiting the stalks of mature plants. A. zeae grows most vigorously on artificial media containing corn cob xylan, suggesting that A. zeae might be a source of hemicellulolytic enzymes uniquely adapted for the utilization of corn cell wall components. An examination of A. zeae grown on corn fiber found that it possesses a full complement of hemicellulolytic enzymes including xylanases, xylosidases, and arabinofuranosidases capable of releasing greater than 90% of xylose and arabinose from corn cob and wheat arabinoxylans. A 30 kDa arabinofuranosidase (AF30) and a 47 kDa arabinofuranosidase (AF47) were purified from the cell-free culture supernatant by ion-exchange and hydrophobic interaction chromatography. AF30, which does not bind to the anion exchange support at pH 6.5, has a Km for 4-nitrophenyl-α-L-arabinofuranoside (4NPA) of 8.6 mM and Vmax of 3.2 U/mg. Temperature and pH optima are 45°C and pH 4.5. TLC analysis of the hydrolysis products indicated that AF30 releases primarily arabinose and some xylobiose from corn fiber arabinoxylan. AF47, which binds to the anion-exchange support, has a Km for 4NPA of 4.4 mM and Vmax of 1.7 U/mg. Temperature and pH optima are 32°C and pH 6.0. The enzymes produced by A. zeae may have industrial application for the hydrolysis of recalcitrant lignocellulosic feedstocks such as corn fiber.