Supplementation effect of compatible solute ectoine on the ethanol fermentation by Zymomonas mobilis CICC10232 was examined in the presence of high glucose concentration. Addition of ectoine promoted the cell growth as well as volumetric ethanol productivity in the presence of 250 g/l of glucose. At the end of ethanol fermentation, cell dry weight resulted in 1.8 and 1.5 g CDW/l in the presence and absence of 1 mM ectoine, respectively. Volumetric ethanol productivity in the presence of I mM ectoine became 1.1 g/l/h, which resulted in 57.1% higher than that in the absence of ectoine, 0.7 g/l/h. In addition, fermentation time was shortened by 24 h when 1 mM ectoine existed in the medium. In the presence of 250 g/l of glucose together with various concentrations of ectoine, relative enzyme activities of glucokinase (GK), glucose-6-phosphate dehydrogenase (G-6-PDH), and alcohol dehydrogenase (ADH) increased by 29.9, 11.6, and 7.7% in the presence of 0.5, 0.5, and 0.25 mM ectoine compared to those without ectoine supplemented, respectively. The promoting function of ectoine on ethanol fermentation may be related to the protection of these enzyme activities under osmotic stress. (C) 2008 Elsevier Ltd. All rights reserved.