Influence of fermentation conditions on levan production by Zymomonas mobilis CT2

Abstract

Zymomonas mobilis produces two extracellular sucrases namely levansucrase (sac B) and sucrase (sac C). A mutant strain of Z. mobilis CT2 defective in sucrase sac C, constructed earlier by gene disruption 1 , produced higher levels of levan (27.2 g L -1 ) than the parent strain B14023 (15.4 g L -1 ) from 200 g L -1 of sucrose at 25°C and pH 5.0. Increasing fermentation temperature from 25 to 35°C enhanced ethanol concentration from 17.8 to 46.4 g L -1 due to increased rate of sucrose hydrolysis but decreased the transfructosylation activity from 165 to 56 U mL -1 . Addition of glucose or fructose to the fermentation medium considerably reduced the levan production due to the inhibition of levansucrase activity.