Understanding the stress responses of Kluyveromyces marxianus after an arrest during high-temperature ethanol fermentation based on integration of RNA-Seq and metabolite data

• Published in: Applied microbiology and biotechnology 2019-03, Vol.103 (6), p.2715-2729
• Main Authors: Fu, Xiaofen, Li, Pengsong, Zhang, Lei, Li, Shizhong
• Format: Article
• Language: English
• Subjects: Acetic acid; Acid production; Amino acids; Ascomycota; Biomedical and Life Sciences; Biosynthesis; Biotechnology; Branched chain amino acids; Chain branching; Deoxyribonucleic acid; DNA; DNA repair; Electron transport; Ergosterol; Ethanol; Fatty acids; Fermentation; Flavin mononucleotide; Gene expression; Gene sequencing; Genes; Genetic aspects; Genomics; Glycerol; High temperature; Integration; Iron compounds; Kluyveromyces marxianus; Life Sciences; Lipid composition; Lipids; Metabolic engineering; Metabolites; Methods; Microbial Genetics and Genomics; Microbiology; Mitochondria; NADH; NADP; NADPH-diaphorase; Niacinamide; Nicotinamide; Nicotinamide adenine dinucleotide; Organic acids; Peroxidase; Phosphates; Phytosterols; Plant lipids; Production management; Proteomics; Purines; Reactive oxygen species; Regeneration; Reoxidation; Ribonucleic acid; RNA; RNA sequencing; Steroids (Organic compounds); Sulfur; Sulfur compounds; Temperature effects; Transcriptomics; Tricarboxylic acid cycle; Yeast; Yeasts
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-019-09637-x

The thermotolerant Kluyveromyces marxianus is a potential candidate for high-temperature ethanol fermentation. Although K. marxianus exhibited high ethanol productivity at 45 °C during the early fermentation stage, we observed a fermentation arrest due to the accumulated inhibitors. The stress responses of K. marxianus during high-temperature fermentation were revealed based on integration of RNA sequencing (RNA-Seq) and metabolite data. High temperature stimulated mitochondrial respiration but repressed the tricarboxylic acid (TCA) cycle, leading to increased generation of reactive oxygen species (ROS) and a lowered ratio of reduced nicotinamide adenine dinucleotide (NADH)/oxidized nicotinamide adenine dinucleotide (NAD + ). Glycerol production was enhanced during the early fermentation stage, which might contribute to NADH reoxidation and ROS generation. Excess ROS could be neutralized by reduced nicotinamide adenine dinucleotide phosphate (NADPH) that might be reserved in the following ways: (1) decreased biosynthesis of branched-chain amino acids (BCAAs) reduced NADPH consumption; (2) enhanced acetic acid production increased NADPH regeneration. The degree of fatty acid unsaturation was also reduced to adapt to high temperature. In addition, stress responses were also observed after the fermentation arrest at 45 °C. Genes related to peroxidase activity, iron-sulfur cluster assembly, and flavin mononucleotide (FMN) binding were downregulated, while genes associated with DNA repair and lipid composition of the plasma were upregulated. The yeast also produced more ergosterol to deal with ethanol stress. This study gains comprehensive insights into the K. marxianus transcriptome under various stresses during high-temperature ethanol fermentation, providing rich information for further metabolic engineering towards improved stress tolerance and ethanol production.