Changes in intracellular metabolism underlying the adaptation of Saccharomyces cerevisiae strains to ethanol stress

Exogenous Trehalose Assists Zygosaccharomyces rouxii in Resisting High-Temperature Stress Mainly by Activating Genes Rather than Entering Metabolism

Zygosaccharomyces rouxii is a typical aroma-producing yeast in food brewing, but it has low heat resistance and poor proliferation ability at high temperature. Trehalose is generally considered to be a protective agent that helps stable yeast cells resist heat shock stress, but its functional mechanism for yeast cells in the adaptation period under heat stress is unclear. In this study, the physiological metabolism changes, specific gene transcription expression characteristics, and transcriptome differences of Z. rouxii under different carbon sources under high-temperature stress (40 °C) were compared to explore the mechanism of trehalose inducing Z. rouxii to recover and proliferate under high-temperature stress during the adaptation period. The results showed that high concentration of trehalose (20% Tre) could not be used as the main carbon source for the proliferation of Z. rouxii under long-term high-temperature stress, but it helped to maintain the stability of the cell population. The intracellular trehalose of Z. rouxii was mainly derived from the synthesis and metabolism of intracellular glucose, and the extracellular acetic acid concentration showed an upward trend with the improvement of yeast growth. A high concentration of trehalose (20% Tre) can promote the expression of high glucose receptor gene GRT2 (12.0-fold) and induce the up-regulation of HSF1 (27.1-fold), MSN4 (58.9-fold), HXK1 (8.3-fold), and other signal transduction protein genes, and the increase of trehalose concentration will maintain the temporal up-regulation of these genes. Transcriptome analysis showed that trehalose concentration and the presence of glucose had a significant effect on the gene expression of Z. rouxii under high-temperature stress. In summary, trehalose assists Z. rouxii in adapting to high temperature by changing gene expression levels, and assists Z. rouxii in absorbing glucose to achieve cell proliferation.

Analysis of the ethanol stress response mechanism in Wickerhamomyces anomalus based on transcriptomics and metabolomics approaches

Background

Wickerhamomyces anomalus (W. anomalus) is a kind of non-Saccharomyces yeast that has a variety of unique physiological characteristics and metabolic features and is widely used in many fields, such as food preservation, biomass energy, and aquaculture feed protein production. However, the mechanism of W. anomalus response to ethanol stress is still unclear, which greatly limits its application in the production of ethanol beverages and ethanol fuels. Therefore, we checked the effects of ethanol stress on the morphology, the growth, and differentially expressed genes (DEGs) and metabolites (DEMs) of W. anomalus.

Results

High concentrations of ethanol (9% ethanol and 12% ethanol) remarkably inhibited the growth of W. anomalus. Energy metabolism, amino acid metabolism, fatty acids metabolism, and nucleic acid metabolism were significantly influenced when exposing to 9% ethanol and 12% ethanolstress, which maybe universal for W. anomalus to response to different concentrations of ethanol stressl Furthermore, extracellular addition of aspartate, glutamate, and arginine significantly abated ethanol damage and improved the survival rate of W. anomalus.

Conclusions

The results obtained in this study provide insights into the mechanisms involved in W. anomalus response to ethanol stress. Therefore, new strategies can be realized to improve the ethanol tolerance of W. anomalus through metabolic engineering.

Effects of ethanol stress on epsilon-poly-l-lysine (ε-PL) biosynthesis in Streptomyces albulus X-18

The aim of the study was to reveal the effects of ethanol stress on the production of epsilon-poly-l-lysine (ε-PL) in Streptomyces albulus X-18. The results showed that biomass and the utilization of glucose were respectively increased by ethanol stress. The ε-PL yield was increased by 41.42 % in the shake flask and 37.02 % in 10 L fermenter with 1% (v/v) ethanol. The morphology of colonies and mycelia showed significant differences. The intracellular reactive oxygen species level was increased by about 100 %. The ratio of unsaturated fatty acids to saturated fatty acids in the cell membrane was increased by ethanol stress. Isobaric Tags for Relative and Absolute Quantitation (iTRAQ) proteomic profile showed that 265 identified proteins were differentially expressed. The differentially expressed proteins (DEPs) were mainly involved in biological processes. The up-regulated DEPs were mainly involved in the redox reaction and stress response. The metabolic flux of l-Asp was shifted to l-Lys biosynthesis, and the DAP pathway was strengthened. Protein-protein interaction analysis showed that 30 DEPs interacted with l-Lys biosynthesis. The changes of ten proteins by Parallel Reaction Monitoring (PRM) were consistent with those by iTRAQ. The study provided valuable clues to better understand the mechanism of ε-PL biosynthesis improvement by ethanol stress.

Metabolic Response of Pleurotus ostreatus to Continuous Heat Stress

Heat stress seriously threatens the growth of Pleurotus ostreatus. Various studies have been performed to study the resistance of P. ostreatus to heat stress. Here, the metabolome was evaluated to determine the response of P. ostreatus mycelia to heat stress at different times (6, 12, 24, 48 h). More than 70 differential metabolites were detected and enriched in their metabolic pathways. Dynamic metabolites changes in enrichment pathways under heat stress showed that heat stress enhanced the degradation of unsaturated fatty acids and nucleotides, increased the content of amino acids and vitamins, and accelerated glycolysis and the tricarboxylic acid cycle in P. ostreatus. The time course changes of P. ostreatus metabolites under continuous heat stress demonstrated that amino acids continuously changed with heat stress, nucleotides clearly changed with heat stress at 12 and 48 h, and lipids exhibited an increasing trend with prolonged heat stress, while few types saccharides and vitamins changed under heat stress. Additionally, heat-treated P. ostreatus produced salicylic acid and other stress-resistant substances that were reported in plants. This study first reported the metabolites changes in P. ostreatus mycelia during 48 h of heat stress. The metabolic pathways and substances that changed with heat stress in this research will aid future studies on the resistance of P. ostreatus and other edible fungi to heat stress.

New Insights Into the Response of Metabolome of Escherichia coli O157:H7 to Ohmic Heating

The objective of this study was to investigate the effects of ohmic heating and water bath heating (WB) on the metabolome of Escherichia coli O157:H7 cells at the same inactivation levels. Compared to low voltage long time ohmic heating (5 V/cm, 8.50 min, LVLT) and WB (5.50 min), the high voltage short time ohmic heating (10 V/cm, 1.75 min, HVST) had much shorter heating time. Compared to the samples of control (CT), there were a total of 213 differential metabolites identified, among them, 73, 78, and 62 were presented in HVST, LVLT, and WB samples, revealing a stronger metabolomic response of E. coli cells to HVST and LVLT than WB. KEGG enrichment analysis indicated that the significantly enriched pathways were biosynthesis and metabolism of amino acids (alanine, arginine, aspartate, and glutamate, etc.), followed by aminoacyl-tRNA biosynthesis among the three treatments. This is the first metabolomic study of E. coli cells in response to ohmic heating and presents an important step toward understanding the mechanism of ohmic heating on microbial inactivation, and can serve as a theoretical basis for better application of ohmic heating in food products.