Saccharomyces cerevisiae Y5 (CGMCC no. 2660) and Issatchenkia orientalis Y4 (CGMCC no. 2159) were combined individually with Pichia stipitis CBS6054 to establish the cocultures of Y5 + CBS6054 and Y4 + CBS6054. The coculture Y5 + CBS6054 effectively metabolized furfural and HMF and converted xylose and glucose mixture to ethanol with ethanol concentration of 16.6？g/L and ethanol yield of 0.46？g ethanol/g sugar, corresponding to 91.2% of the maximal theoretical value in synthetic medium. Accordingly, the nondetoxified dilute-acid hydrolysate was used to produce ethanol by co-culture Y5 + CBS6054. The co-culture consumed glucose along with furfural and HMF completely in 12？h, and all xylose within 96？h, resulting in a final ethanol concentration of 27.4？g/L and ethanol yield of 0.43？g ethanol/g sugar, corresponding to 85.1% of the maximal theoretical value. The results indicated that the co-culture of Y5 + CBS6054 was a satisfying combination for ethanol production from non-detoxified dilute-acid lignocellulosic hydrolysates. This co-culture showed a promising prospect for industrial application. 1. Introduction Cellulosic ethanol has been widely regarded as a promising alternative liquid fuel due to its projected positive attributes in terms of economic, environmental, and social sustainability [1–3]. The ability to generate and convert fermentable sugars from lignocellulosic materials to ethanol is the central technological challenge [4, 5]. The fermentability of a hydrolysate is strongly dependent on the feedstock, the pretreatment method, and the strain selected. Most biomass feedstock contains a significant amount of xylan that is converted to xylose through hydrolysis. Most biomass pretreatment methods, applied to remove barriers to enzymatic cellulose saccharification, produce fermentation inhibitors. Therefore the selected strain needs to be capable of fermenting xylose and glucose with good toleration of inhibitors. Dilute-acid pretreatment is one of the most promising pretreatment methods for sugar production from lignocelluloses and has been widely studied [6]. However it produces fermentation inhibitory compounds, such as furfural and HMF, the most investigated and the most highly toxic inhibitors. A furfural concentration as high as 1.5？g L？1 could interfere respiration and growth of microorganisms, which resulted in the reduction of ethanol yield and productivity by 90.4% and 85.1%, respectively [7]. The inhibitive effect of HMF is similar to that of furfural, causing an extended lag phase during the growth of microorganism cells. Pichia
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