GSE178100
RNA-seq based transcriptomic analysis of the non-conventional yeast Spathaspora passalidarum during Melle-boinot cell recycle in xylose-glucose mixtures
The Mellet-boinot is a promising process to be applied for second-generation ethanol production by wild yeasts. However, the impact of this process on the physiology and fermentative performance of the xylose-fermenting yeast Spathaspora passalidarum during second-generation ethanol production, remains elusive. Therefore, we have conducted a deep transcriptomic analysis of S. passalidarum during five consecutive fed-batches and cell recycles, to determine the differences and global responses of differentially expressed genes (DEGs) during the Melle-Boinot process. A physiological adaptation was observed resulting in an increase on ethanol yield, ethanol volumetric productivity and ethanol titer. Furthermore, a decrease of the subproduct xylitol was also observed.  A transcriptional regulation was achieved from the third cell recycle onwards and this regulation was maintained afterwards. Analysing the DEGs during the recycles showed an up-regulation of  genes involved in ATP synthesis, N-Glycan biosynthesis, oxidative phosphorylation and purine metabolism, indicating as important mechanisms for adaptation throughout recycles due increased ethanol concentration. Moreover, the TCA cycle anabolic pathway, gluconeogenesis, glycogen and trehalose biosynthesis, fatty acid and sterol biosynthesis were also affected mainly due ethanol concentration and osmotic pressure implying that cell energy was generated towards the production of cell wall components in order to S. passalidarum cells to thrive in consecutive recycles. Taken together these results demonstrate that the Melle-Boinot process is a worthy strategy to be applied on 2G ethanol fermentation by native yeasts. Furthermore, we highlight major microbial molecular strategies for xylose conversion providing relevant insights for further metabolic engineering aiming to improve 2G bioethanol production. Overall design: We have conducted a deep transcriptomic analysis of S. passalidarum during five consecutive fed-batches and cell recycles, to determine the differences and global responses of differentially expressed genes (DEGs) during the Melle-Boinot fermentation process.