It is of utmost importance to construct industrial xylose-fermenting Saccharomyces cerevisiae strains for lignocellulosic bioethanol production. In this study, two xylose isomerase-based industrial S. cerevisiae strains, O7 and P5, were constructed by δ-integration of the xylose isomerase (XI) gene xylA from the fungus Orpinomyces sp. and from the bacterium Prevotella ruminicola, respectively. The xylose consumption of the strains O7 and P5 at 48-h fermentation was 17.71 and 26.10 g/L, respectively, in synthetic medium with xylose as the sole sugar source. Adaptive evolution further improved the xylose fermentation capacity of the two strains to 51.0 and 28.9% in average, respectively. The transcriptomes of these two strains before and after evolution were analyzed using RNA-Seq. The expression levels of the genes involved in cell integrity, non-optimal sugar utilization, and stress response to environment were significantly up-regulated after evolution and did not depend on the origin of xylA; the expression levels of the genes involved in transmembrane transport, rRNA processing, cytoplasmic translation, and other processes were down-regulated. The expression of genes involved in central carbon metabolism was fine-tuned after the evolution. The analysis of transcription factors (TFs) indicated that most of the genes with significant differential expression were regulated by the TFs related to cell division, DNA damage response, or non-optimal carbon source utilization. The results of this study could provide valuable references for the construction of efficient xylose-fermenting XI strains.
Keywords: Adaptive evolution; Industrial Saccharomyces cerevisiae; Transcriptome analysis; Xylose isomerase; δ-Integration.