P8: Thermo-activated xylanases from tropical strains of Aureobasidium pullulans

From various foliar samples collected in 4 provinces in Thailand, 20 strains of Aureobasidium pullulans were obtained.  All strains were positive for xylanase production when grown on Yeast Malt Xylan Agar.  In liquid culture, these A. pullulans strains produced xylanase ranging from 31 to 205 U.l^-1.  The stability of these enzymes at high temperature varied widely.  Incubation at 60°C for 1 hour showed activation of enzymes from 6 strains in comparison to their counterparts stored at 4°C for 1 hour.  Xylanases from the other 14 strains were more sensitive to high temperature, losing most of their activity after 1 hour at 60°C.  Thermo-activated xylanases were divided into 2 groups based on their responses to longer incubation times at 60°C.  Xylanases in the first group showed a 2.5- to 4-fold increase in activity after 1 hour but completely lost their activity within 5 hours whereas those in the second group exhibited a 2- to 2.4-fold increase in activity after 1 hour and retained more than half of their activity after 5 hours.  Clearly there is an interesting range of diversity in the thermostability of these Thai A. pullulans xylanases.