Isolation of Aureobasidium pullulans from Zimbabwean sources and glucosidase activities of selected isolates

The yeast-like fungus Aureobasidium pullulans (DeBary) Arnaud has been isolated and identified for the first time in Zimbabwe from diverse sources including fruits, leaves and commercial manure. Selective enrichment of an appropriate substrate using a minimal salts broth with shaking for two days at 25°C followed by plating on a corresponding solid medium, proved to be a reliable method for isolating the fungus. Extracellular α and ß-glucosidases produced in broth cultures by selected isolates were generally low; yields ranged from 0.7–1.4 units/ml and 1.7–2.5 units/ml respectively. Of six (mainly complex) nitrogen sources, NaNO3 supported the highest level of extracellular α-glucosidase in A. pullulans Mn2 despite a very low final pH (2.42). However, addition of Tween 80 to a 24 hour old culture led to a three-fold increase in yield of extracellular α-glucosidase (approx. 6.0U/ml).