Fig. 2

Fermentation performance of a control strain without XI and strains containing plasmid vectors expressing various XIs in glucose/xylose co-fermentation under micro-aerobic conditions. Batch fermentation examinations were performed using cultures inoculated with cells at high density (OD_A600 = 20) under micro-aerobic conditions. A control strain lacking XI (SS36) and eight strains expressing XIs (SS37 to SS44) were grown in 70 mL YPD₈₅X₃₅ medium containing G418 (200 µg/mL) at 30 °C. Samples of culture medium were collected at 0, 1, 3, 6, 12, 24, 36, 48, 60 and 72 h (10 times) for HPLC analysis of metabolites. The XIs were introduced episomally via low copy number plasmids into the same parental strain, SS29. The dots and error bars in the panels represent the mean concentrations and standard deviations, respectively, of the following metabolites measured in biological triplicates: glucose (blue), xylose (red), xylitol (yellow green), glycerol (purple), acetate (light blue) and ethanol (orange). The details for the metabolite concentrations are shown in Additional file 2: Table S2