Studies On Xylose Metabolism Of Natural Yeast Spathaspora Passalidarum

The cost-effective utilization of xylose is one of the important bottlenecks for the production of bioethanol using biomass as feedstock. Recently, Spathaspora passalidarum was characterized to be able to utilize xylose even under anaerobic condition. This capacity eliminates the problem of accurate oxygen regulation which is indispensable to many other xylose-fermenting yeasts for conversing xylose to bioethanol. Interestingly,5. passalidarum has two xylose reductases (XYL1.1and1.2) and two xylitol dehydrogenases (XYL2.1and2.2) based on genome annotation. To investigate the role of these enzymes in aerobic or anaerobic xylose metabolism of S, passalidarum, in this study, XYL1.1,1.2,2.1and2.2were in vivo and in vitro characterized. Both recombinant XYL1.1and XYL1.2can use NADPH and NADH as cofactor, but with preference for NADH. Moreover, XYL1.1has higher affinity for NADH than XYL1.2. Meanwhile, XYL1.1increased the level of transcription while XYL1.2decreased the level of transcription in S. passalidarum under anaerobic condition via transcriptional analysis. Recombinant XYL2.1and XYL2.2only use NAD+as cofactor, and XYL2.2has very low level of transcription whether under aerobic or anaerobic condition in S. passalidarum. With these results, we concluded that oxygen could fine-tune the expression of XYL1.1and XYL1.2for improving xylose utilization. In addition, only XYL2.1, not XYL2.2, acts on the process of xylose metabolism. These results would contribute to improving xylose utilization by genetic engineering strategies.