Rapamycin enhanced the production of 2-phenylethanol during whole-cell bioconversion by yeast

Enhanced multistress tolerance of Saccharomyces cerevisiae with the sugar transporter-like protein Stl1F427L mutation in the presence of glycerol

During microbial industrial production, microorganisms often face diverse stressors, including organic solvents, high salinity, and high sugar levels. Enhancing microorganism tolerance to such stresses is crucial for producing high-value-added products. Previous studies on the mechanisms of 2-phenylethanol (2-PE) tolerance in Saccharomyces cerevisiae revealed a potential connection between the sugar transporter-like protein (Stl1) mutation (F427L) and increased tolerance to high sugar and salt stress, suggesting a broader role in multistress tolerance. Herein, we showed that the Stl1F427L mutant strain (STL) exhibits significantly improved multistress tolerance in the presence of glycerol. Molecular dynamics simulations indicated that Stl1F427L may enhance glycerol molecular binding, resulting in a significant increase in the intracellular glycerol content of the mutant strain STL. Additionally, under multistress conditions, pyruvate and ergosterol levels and catalase (CAT) and superoxide dismutase (SOD) activities were significantly increased in the mutant strain STL compared with the control strain 5D. This resulted in a notable increase in cell membrane toughness and a decrease in intracellular reactive oxygen species levels. These findings highlight the mechanism by which Stl1F427L enhances S. cerevisiae tolerance to multistress. Importantly, they provide novel insights into and methodologies for improving the resilience of industrial microorganisms.

IMPORTANCE

Stl1F427L exhibits improved strain tolerance to multistress when adding glycerol, may enhance glycerol molecular binding, and can make a significant increase in intracellular glycerol content. It can reduce reactive oxygen species levels and increase ergosterol content. This paper provides novel insights and methods to get robust industrial microorganisms.

Metabolic engineering of the oleaginous yeast Yarrowia lipolytica for 2-phenylethanol overproduction

The rose fragrance molecule 2-phenylethanol (2-PE) has huge market demand in the cosmetics, food and pharmaceutical industries. However, current 2-PE synthesis methods do not meet the efficiency market requirement. In this study, CRISPR-Cas9-related metabolic engineering strategies were applied to Yarrowia lipolytica for the de novo biosynthesis of 2-PE. Initially, overexpressing exogenous feedback-resistant EcAROGfbr and EcPheAfbr increased 2-PE production to 276.3 mg/L. Subsequently, the ylARO10 and ylPAR4 from endogenous genes were enhanced with the multi-copies to increase the titer to 605 mg/L. Knockout of ylTYR1 and enhancement of shikimate pathway by removing the precursor metabolic bottleneck and overexpressing the genes ylTKT, ylARO1, and ylPHA2 resulted in a significant increase of the 2-PE titer to 2.4 g/L at 84 h, with the yield of 0.06 g/gglu, which is the highest yield for de novo synthesis in yeast. This study provides a valuable precedent for the efficient biosynthesis of shikimate pathway derivatives.

Exploring the stress response mechanisms to 2-phenylethanol conferred by Pdr1p mutation in Saccharomyces cerevisiae

BACKGROUND

The 2-phenylethanol (2-PE) tolerance phenotype is crucial to the production of 2-PE, and Pdr1p mutation can significantly increase the tolerance of 2-PE in Saccharomyces cerevisiae. However, its underlying molecular mechanisms are still unclear, hindering the rational design of superior 2-PE tolerance performance.

RESULTS

Here, the physiology and biochemistry of the PDR1_862 and 5D strains were analyzed. At 3.5 g/L 2-PE, the ethanol concentration of PDR1_862 decreased by 21%, and the 2-PE production of PDR1_862 increased by 16% than those of 5D strain. Transcriptome analysis showed that at 2-PE stress, Pdr1p mutation increased the expression of genes involved in the Ehrlich pathway. In addition, Pdr1p mutation attenuated sulfur metabolism and enhanced the one-carbon pool by folate to resist 2-PE stress. These metabolic pathways were closely associated with amino acids metabolism. Furthermore, at 3.5 g/L 2-PE, the free amino acids content of PDR1_862 decreased by 31% than that of 5D strain, among the free amino acids, cysteine was key amino acid for the enhancement of 2-PE stress tolerance conferred by Pdr1p mutation.

CONCLUSIONS

The above results indicated that Pdr1p mutation enhanced the Ehrlich pathway to improve 2-PE production of S. cerevisiae, and Pdr1p mutation altered the intracellular amino acids contents, in which cysteine might be a biomarker in response to Pdr1p mutation under 2-PE stress. The findings help to elucidate the molecular mechanisms for 2-PE stress tolerance by Pdr1p mutation in S. cerevisiae, identify key metabolic pathway responsible for 2-PE stress tolerance.

Depletion of cap-binding protein eIF4E dysregulates amino acid metabolic gene expression

Protein synthesis is metabolically costly and must be tightly coordinated with changing cellular needs and nutrient availability. The cap-binding protein eIF4E makes the earliest contact between mRNAs and the translation machinery, offering a key regulatory nexus. We acutely depleted this essential protein and found surprisingly modest effects on cell growth and recovery of protein synthesis. Paradoxically, impaired protein biosynthesis upregulated genes involved in the catabolism of aromatic amino acids simultaneously with the induction of the amino acid biosynthetic regulon driven by the integrated stress response factor GCN4. We further identified the translational control of Pho85 cyclin 5 (PCL5), a negative regulator of Gcn4, that provides a consistent protein-to-mRNA ratio under varied translation environments. This regulation depended in part on a uniquely long poly(A) tract in the PCL5 5' UTR and poly(A) binding protein. Collectively, these results highlight how eIF4E connects protein synthesis to metabolic gene regulation, uncovering mechanisms controlling translation during environmental challenges.

Enzymatic properties and inhibition tolerance analysis of key enzymes in β-phenylethanol anabolic pathway of Saccharomyces cerevisiae HJ

Huangjiu is known for its unique aroma, primarily attributed to its high concentration of β-phenylethanol (ranging from 40 to 130 mg/L). Phenylalanine aminotransferase Aro9p and phenylpyruvate decarboxylase Aro10p are key enzymes in the β-phenylethanol synthetic pathway of Saccharomyces cerevisiae HJ. This study examined the enzymatic properties of these two enzymes derived from S. cerevisiae HJ and S288C. After substrate docking, Aro9pHJ (-24.05 kJ/mol) and Aro10pHJ (-14.33 kJ/mol) exhibited lower binding free energies compared to Aro9pS288C (-21.93 kJ/mol) and Aro10pS288C (-12.84 kJ/mol). ARO9 and ARO10 genes were heterologously expressed in E. coli BL21. Aro9p, which was purified via affinity chromatography, showed inhibition by l-phenylalanine (L-PHE), but the reaction rate Vmax(Aro9pHJ: 23.89 μmol·(min∙g)-1) > Aro9pS288C: 21.3 μmol·(min∙g)-1) and inhibition constant Ki values (Aro9pHJ: 0.28 mol L-1>Aro9pS288C 0.26 mol L-1) indicated that Aro9p from S. cerevisiae HJ was more tolerant to substrate stress during Huangjiu fermentation. In the presence of the same substrate phenylpyruvate (PPY), Aro10pHJ exhibited a stronger affinity than Aro10pS288C. Furthermore, Aro9pHJ and Aro10pHJ were slightly more tolerant to the final metabolites β-phenylethanol and ethanol, respectively, compared to those from S288C. The study suggests that the mutations in Aro9pHJ and Aro10pHJ may contribute to the increased β-phenylethanol concentration in Huangjiu. This is the first study investigating enzyme tolerance mechanisms in terms of substrate and product, providing a theoretical basis for the regulation of the β-phenylethanol metabolic pathway.

Dysregulation of amino acid metabolism upon rapid depletion of cap-binding protein eIF4E

Protein synthesis is a crucial but metabolically costly biological process that must be tightly coordinated with cellular needs and nutrient availability. In response to environmental stress, translation initiation is modulated to control protein output while meeting new demands. The cap-binding protein eIF4E-the earliest contact between mRNAs and the translation machinery-serves as one point of control, but its contributions to mRNA-specific translation regulation remain poorly understood. To survey eIF4E-dependent translational control, we acutely depleted eIF4E and determined how this impacts protein synthesis. Despite its essentiality, eIF4E depletion had surprisingly modest effects on cell growth and protein synthesis. Analysis of transcript-level changes revealed that long-lived transcripts were downregulated, likely reflecting accelerated turnover. Paradoxically, eIF4E depletion led to simultaneous upregulation of genes involved in catabolism of aromatic amino acids, which arose as secondary effects of reduced protein biosynthesis on amino acid pools, and genes involved in the biosynthesis of amino acids. These futile cycles of amino acid synthesis and degradation were driven, in part, by translational activation of GCN4, a transcription factor typically induced by amino acid starvation. Furthermore, we identified a novel regulatory mechanism governing translation of PCL5, a negative regulator of Gcn4, that provides a consistent protein-to-mRNA ratio under varied translation environments. This translational control was partial dependent on a uniquely long poly-(A) tract in the PCL5 5' UTR and on poly-(A) binding protein. Collectively, these results highlight how eIF4E connects translation to amino acid homeostasis and stress responses and uncovers new mechanisms underlying how cells tightly control protein synthesis during environmental challenges.