Overexpression of ethionine resistance gene for maximized production of S-adenosylmethionine in Saccharomyces cerevisiae sake kyokai No. 6

Improvement of S-adenosyl-L-methionine production in Saccharomyces cerevisiae by atmospheric and room temperature plasma-ultraviolet compound mutagenesis and droplet microfluidic adaptive evolution

To improve S-Adenosyl-L-methionine (a compound with important physiological functions, SAM) production, atmospheric and room temperature plasma and ultraviolet-LiCl mutagenesis were carried out with Saccharomyces cerevisiae strain ZY 1-5. The mutants were screened with ethionine, L-methionine, nystatin and cordycepin as screening agents. Adaptive evolution of a positive mutant UV6-69 was further performed by droplet microfluidics cultivation with ethionine as screening pressure. After adaptation, mutant T11-1 was obtained. Its SAM titer in shake flask fermentation reached 1.31 g/L, which was 191% higher than that of strain ZY 1-5. Under optimal conditions, the SAM titer and biomass of mutant T11-1 in 5 L bioreactor reached 10.72 g/L and 105.9 g dcw/L (142.86% and 34.22% higher than those of strain ZY 1-5), respectively. Comparative transcriptome analysis between strain ZY 1-5 and mutant T11-1 revealed the enhancements in TCA cycle and gluconeogenesis/glycolysis pathways as well as the inhibitions in serine and ergosterol synthesis of mutant T11-1. The elevated SAM synthesis of mutant T11-1 may attribute to the above changes. Taken together, this study is helpful for industrial production of SAM.

Combination of Three Methods to Reduce Glucose Metabolic Rate For Improving N-Acetylglucosamine Production in Saccharomyces cerevisiae

Previously, the production of N-acetylglucosamine (GlcNAc) in Saccharomyces cerevisiae was improved by deletion of the genes encoding phosphofructokinase 2 (PFK-2) isoforms, which reduced the glycolytic flux by eliminating the pathway to produce fructose-2,6-bisphosphate, an allosteric activator of phosphofructokinase 1 (PFK-1). We further examined the effects of an additional reduction in glucose metabolic rate on N-acetylglucosamine production. Glucose uptake rate was lowered by expressing a gene encoding truncated glucose-sensing regulator ( MTH1-Δ T). In addition, catalytically dead Cas9 (dCas9) was introduced in order to down-regulate the expression levels of PFK-1 and pyruvate kinase-1 (Pyk1). Finally, the three strategies were introduced into S. cerevisiae strains in a combinatorial way; the strain containing all three modules resulted in the highest N-acetylglucosamine production yield. The results showed that the three modules cooperatively reduced the glucose metabolism and improved N-acetylglucosamine production up to 3.0 g/L in shake flask cultivation.

Stimulating S-adenosyl-l-methionine synthesis extends lifespan via activation of AMPK

Dietary restriction (DR), such as calorie restriction (CR) or methionine (Met) restriction, extends the lifespan of diverse model organisms. Although studies have identified several metabolites that contribute to the beneficial effects of DR, the molecular mechanism underlying the key metabolites responsible for DR regimens is not fully understood. Here we show that stimulating S-adenosyl-l-methionine (AdoMet) synthesis extended the lifespan of the budding yeast Saccharomyces cerevisiae The AdoMet synthesis-mediated beneficial metabolic effects, which resulted from consuming both Met and ATP, mimicked CR. Indeed, stimulating AdoMet synthesis activated the universal energy-sensing regulator Snf1, which is the S. cerevisiae ortholog of AMP-activated protein kinase (AMPK), resulting in lifespan extension. Furthermore, our findings revealed that S-adenosyl-l-homocysteine contributed to longevity with a higher accumulation of AdoMet only under the severe CR (0.05% glucose) conditions. Thus, our data uncovered molecular links between Met metabolites and lifespan, suggesting a unique function of AdoMet as a reservoir of Met and ATP for cell survival.

Glucose-based microbial production of the hormone melatonin in yeast Saccharomyces cerevisiae

Melatonin is a natural mammalian hormone that plays an important role in regulating the circadian cycle in humans. It is a clinically effective drug exhibiting positive effects as a sleep aid and a powerful antioxidant used as a dietary supplement. Commercial melatonin production is predominantly performed by complex chemical synthesis. In this study, we demonstrate microbial production of melatonin and related compounds, such as serotonin and N‐acetylserotonin. We generated Saccharomyces cerevisiae strains that comprise heterologous genes encoding one or more variants of an L‐tryptophan hydroxylase, a 5‐hydroxy‐L‐tryptophan decarboxylase, a serotonin acetyltransferase, an acetylserotonin O‐methyltransferase, and means for providing the cofactor tetrahydrobiopterin via heterologous biosynthesis and recycling pathways. We thereby achieved de novo melatonin biosynthesis from glucose. We furthermore accomplished increased product titers by altering expression levels of selected pathway enzymes and boosting co‐factor supply. The final yeast strain produced melatonin at a titer of 14.50 ± 0.57 mg L⁻¹ in a 76h fermentation using simulated fed‐batch medium with glucose as sole carbon source. Our study lays the basis for further developing a yeast cell factory for biological production of melatonin.

Genetic basis of metabolome variation in yeast

Metabolism, the conversion of nutrients into usable energy and biochemical building blocks, is an essential feature of all cells. The genetic factors responsible for inter-individual metabolic variability remain poorly understood. To investigate genetic causes of metabolome variation, we measured the concentrations of 74 metabolites across ~ 100 segregants from a Saccharomyces cerevisiae cross by liquid chromatography-tandem mass spectrometry. We found 52 quantitative trait loci for 34 metabolites. These included linkages due to overt changes in metabolic genes, e.g., linking pyrimidine intermediates to the deletion of ura3. They also included linkages not directly related to metabolic enzymes, such as those for five central carbon metabolites to ira2, a Ras/PKA pathway regulator, and for the metabolites, S-adenosyl-methionine and S-adenosyl-homocysteine to slt2, a MAP kinase involved in cell wall integrity. The variant of ira2 that elevates metabolite levels also increases glucose uptake and ethanol secretion. These results highlight specific examples of genetic variability, including in genes without prior known metabolic regulatory function, that impact yeast metabolism.

Genetic modification and bioprocess optimization for S-Adenosyl-L-methionine biosynthesis

S-Adenosyl-L-methionine is an important bioactive sulfur-containing amino acid. Large scale preparation of the amino acid is of great significance. S-Adenosyl-L-methionine can be synthesized from L-methionine and adenosine triphosphate in a reaction catalyzed by methionine adenosyltransferase. In order to enhance S-adenosyl-L-methionine biosynthesis by industrial microbial strains, various strategies have been employed to optimize the process. Genetic manipulation has largely focused on enhancement of expression and activity of methionine adenosyltransferase. This has included its overexpression in Pichia pastoris, Saccharomyces cerevisiae and Escherichia coli, molecular evolution, and fine-tuning of expression by promoter engineering. Furthermore, knocking in of Vitreoscilla hemoglobin and knocking out of cystathionine-β-synthase have also been effective strategies. Besides genetic modification, novel bioprocess strategies have also been conducted to improve S-adenosyl-L-methionine synthesis and inhibit its conversion. This has involved the optimization of feeding modes of methanol, glycerol and L-methionine substrates. Taken together considerable improvements have been achieved in S-adenosyl-L-methionine accumulation at both flask and fermenter scales. This review provides a contemporary account of these developments and identifies potential methods for further improvements in the efficiency of S-adenosyl-L-methionine biosynthesis.