Glucose isomerase production on a xylan-based medium by Bacillus thermoantarcticus

Effects of medium components on intracellular glucose isomerase (GI) production were investigated by Bacillus thermoantarcticus. The highest GI activity was obtained as 1630 U dm−3 in the medium containing (g dm−3): 10.6, birchwood-xylan; 5.6, yeast extract; 5.9 (NH4)2SO4 at T = 55 °C in 33 cm−3 shake-flasks. When birchwood-xylan was replaced with oat spelt- or beechwood-xylan, GI activity decreased to 1372 and 1308 U dm−3, respectively. Effects of pH at uncontrolled-pH (pHUC = 6.0) and controlled-pH (pHC = 6.0) operations, and oxygen transfer at the air inlet rate of 0.5 vvm and agitation rates of 300, 500 and 700 min−1, were investigated in 3.0 dm3 bioreactor system with 1.65 dm3 working volume in the designed medium. The highest GI activity was attained at 500 min−1, 0.5 vvm, pHUC = 6 as 1840 U dm−3 where cell concentration was 2.3 g dm−3. The use of agricultural waste xylan, as the carbon source resulted in concomitant production of xylanase and GI. The highest xylanase activity was attained as 9300 U dm−3 at 500 min−1 and 0.5 vvm. KLa varied between 0.008–0.033 s−1 whereas the highest oxygen uptake rate was 0.002 mmol dm−3 s−1. Initially biochemical reaction limitations were effective; thereafter, mass transfer resistances became more effective.