Influence of fermentation conditions on levan production by <i style="">Zymomonas mobilis</i> CT2

Abstract

<i style="">Zymomonas mobilis</i> produces two extracellular sucrases namely levansucrase (<i style="">sac </i>B) and sucrase (<i style="">sac </i>C). A mutant strain of <i style="">Z. mobilis</i> CT2 defective in sucrase <i style="">sac</i> C, constructed earlier by gene disruption¹, 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 <i style="">p</i>H 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.