Extracellular cellulase production by tropical isolates of Aureobasidium pullulans

Abstract

Cellulase production by Aureobasidium pullulans from the temperate regions has remained speculative, with most studies reporting no activity at all. In the current study, tropical isolates from diverse sources were screened for cellulase production. Isolates were grown on a synthetic medium containing cell walls of Msasa tree (Brachystegia sp.) as the sole carbon source, and their cellulolytic activities were measured using carboxymethyl cellulose and α-cellulose as substrates. All isolates studied produced carboxymethyl cellulase (endoglucanase) and alpha-cellulase (exoglucanase) activity. Endoglucanase-specific activities of ten selected isolates ranged from 2.375 to 12.884 µmol glucose·(mg protein)–1·h–1, while activities on α-cellulose (exoglucanase activity) ranged from 0.293 to 22.442 µmol glucose·(mg protein)–1·day–1. Carboxymethyl cellulose induced the highest cellulase activity in the selected isolates, while the isolates showed variable responses to nitrogen sources. The current study indicates that some isolates of A. pullulans of tropical origin produce significant extracellular cellulolytic activity and that crude cell walls may be good inducers of cellulolytic activity in A. pullulans.Key words: Aureobasidium pullulans, plant cell wall, cellulases, endoglucanase, exoglucanase.