An effective strategy for the co-production of S-adenosyl-l-methionine and glutathione by fed-batch fermentation

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.

The multiple effects of REG1 deletion and SNF1 overexpression improved the production of S-adenosyl-L-methionine in Saccharomyces cerevisiae

BACKGROUND

Saccharomyces cerevisiae is often used as a cell factory for the production of S-adenosyl-L-methionine (SAM) for diverse pharmaceutical applications. However, SAM production by S. cerevisiae is negatively influenced by glucose repression, which is regulated by a serine/threonine kinase SNF1 complex. Here, a strategy of alleviating glucose repression by deleting REG1 (encodes the regulatory subunit of protein phosphatase 1) and overexpressing SNF1 (encodes the catalytic subunit of the SNF1 complex) was applied to improve SAM production in S. cerevisiae. SAM production, growth conditions, glucose consumption, ethanol accumulation, lifespan, glycolysis and amino acid metabolism were analyzed in the mutant strains.

RESULTS

The results showed that the multiple effects of REG1 deletion and/or SNF1 overexpression exhibited a great potential for improving the SAM production in yeast. Enhanced the expression levels of genes involved in glucose transport and glycolysis, which improved the glucose utilization and then elevated the levels of glycolytic intermediates. The expression levels of ACS1 (encoding acetyl-CoA synthase I) and ALD6 (encoding aldehyde dehydrogenase), and the activity of alcohol dehydrogenase II (ADH2) were enhanced especially in the presence of excessive glucose levels, which probably promoted the conversion of ethanol in fermentation broth into acetyl-CoA. The gene expressions involved in sulfur-containing amino acids were also enhanced for the precursor amino acid biosynthesis. In addition, the lifespan of yeast was extended by REG1 deletion and/or SNF1 overexpression. As expected, the final SAM yield of the mutant YREG1ΔPSNF1 reached 8.28 g/L in a 10-L fermenter, which was 51.6% higher than the yield of the parent strain S. cerevisiae CGMCC 2842.

CONCLUSION

This study showed that the multiple effects of REG1 deletion and SNF1 overexpression improved SAM production in S. cerevisiae, providing new insight into the application of the SNF1 complex to abolish glucose repression and redirect carbon flux to nonethanol products in S. cerevisiae.

Glutathione production by Saccharomyces cerevisiae: current state and perspectives

Glutathione (L-γ-glutamyl-cysteinyl-glycine, GSH) is a tripeptide synthesized through consecutive enzymatic reactions. Among its several metabolic functions in cells, the main one is the potential to act as an endogenous antioxidant agent. GSH has been the focus of numerous studies not only due to its role in the redox status of biological systems but also due to its biotechnological characteristics. GSH is usually obtained by fermentation and shows a variety of applications by the pharmaceutical and food industry. Therefore, the search for new strategies to improve the production of GSH during fermentation is crucial. This mini review brings together recent papers regarding the principal parameters of the biotechnological production of GSH by Saccharomyces cerevisiae. In this context, aspects, such as the medium composition (amino acids, alternative raw materials) and the use of technological approaches (control of osmotic and pressure conditions, magnetic field (MF) application, fed-batch process) were considered, along with genetic engineering knowledge, trends, and challenges in viable GSH production. KEY POINTS: • Saccharomyces cerevisiae has shown potential for glutathione production. • Improved technological approaches increases glutathione production. • Genetic engineering in Saccharomyces cerevisiae improves glutathione production.

Improvement of cadaverine production in whole cell system with baker's yeast for cofactor regeneration

Cadaverine, 1,5-diaminopentane, is one of the most promising chemicals for biobased-polyamide production and it has been successfully produced up to molar concentration. Pyridoxal 5'-phosphate (PLP) is a critical cofactor for inducible lysine decarboxylase (CadA) and is required up to micromolar concentration level. Previously the regeneration of PLP in cadaverine bioconversion has been studied and salvage pathway pyridoxal kinase (PdxY) was successfully introduced; however, this system also required a continuous supply of adenosine 5'-triphosphate (ATP) for PLP regeneration from pyridoxal (PL) which add in cost. Herein, to improve the process further a method of ATP regeneration was established by applying baker's yeast with jhAY strain harboring CadA and PdxY, and demonstrated that providing a moderate amount of adenosine 5'-triphosphate (ATP) with the simple addition of baker's yeast could increase cadaverine production dramatically. After optimization of reaction conditions, such as PL, adenosine 5'-diphosphate, MgCl₂, and phosphate buffer, we able to achieve high production (1740 mM, 87% yield) from 2 M L-lysine. Moreover, this approach could give averaged 80.4% of cadaverine yield after three times reactions with baker's yeast and jhAY strain. It is expected that baker's yeast could be applied to other reactions requiring an ATP regeneration system.

Production of L-Theanine Using Escherichia coli Whole-Cell Overexpressing γ-Glutamylmethylamide Synthetase with Bakers Yeast

L-Theanine, found in green tea leaves has been shown to positively affect immunity and relaxation in humans. There have been many attempts to produce L-theanine through enzymatic synthesis to overcome the limitations of traditional methods. Among the many genes coding for enzymes in the L-theanine biosynthesis, glutamylmethylamide synthetase (GMAS) exhibits the greatest possibility of producing large amounts of production. Thus, GMAS from Methylovorus mays No. 9 was overexpressed in several strains including vectors with different copy numbers. BW25113(DE3) cells containing the pET24ma::gmas was selected for strains. The optimal temperature, pH, and metal ion concentration were 50°C, 7, and 5 mM MnCl2, respectively. Additionally, ATP was found to be an important factor for producing high concentration of L-theanine so several strains were tested during the reaction for ATP regeneration. Bakers yeast was found to decrease the demand for ATP most effectively. Addition of potassium phosphate source was demonstrated by producing 4-fold higher L-theanine. To enhance the conversion yield, GMAS was additionally overexpressed in the system. A maximum of 198 mM L-theanine was produced with 16.5 mmol/l/h productivity. The whole-cell reaction involving GMAS has greatest potential for scale-up production of L-theanine.

Improved S-adenosyl-l-methionine production in Saccharomyces cerevisiae using tofu yellow serofluid

S-adenosyl-l-methionine (SAM) has been attracting increasing attention because of its significance in the pharmaceutical industry; however, the high cost of this compound limits its application. Tofu yellow serofluid exhibits high nutritional value and is not costly; therefore, it can be utilized as a substrate in the fermentation industry. In the current study, Saccharomyces cerevisiae was cultured in the tofu yellow serofluid fermentation medium for the SAM biosynthesis. The optimum tofu yellow serofluid fermentation medium contained 70 g/L of glucose, 30 % of yellow serofluid, 20 g/L of l-methionine, and 2.5 g/L of ammonium citrate. Under these conditions, the optimum feeding strategy was established. The results revealed that the dry cell weight (DCW) reached 123.1 g/L, the maximum production of SAM was 16.14 g/L, the highest SAM productivity reached 1.048 g/L/h, and SAM content was determined at 131.1 mg/g DCW. Furthermore, addition of tofu yellow serofluid reduced the average cost of SAM by 31.9 % to compare with the culture process without addition of tofu yellow serofluid. Thus, the tofu yellow serofluid fermentation medium improved the production of SAM and significantly reduced the production costs.

Improving the productivity of S-adenosyl-l-methionine by metabolic engineering in an industrial Saccharomyces cerevisiae strain

S-Adenosyl-l-methionine (SAM) is an important metabolite having prominent roles in treating various diseases. In order to improve the production of SAM, the regulation of three metabolic pathways involved in SAM biosynthesis were investigated in an industrial yeast strain ZJU001. GLC3 encoded glycogen-branching enzyme (GBE), SPE2 encoded SAM decarboxylase, as well as ERG4 and ERG6 encoded key enzymes in ergosterol biosynthesis, were knocked out in ZJU001 accordingly. The results indicated that blocking of either glycogen pathway or SAM decarboxylation pathway could improve the SAM accumulation significantly in ZJU001, while single disruption of either ERG4 or ERG6 gene had no obvious effect on SAM production. Moreover, the double mutant ZJU001-GS with deletion of both GLC3 and SPE2 genes was also constructed, which showed further improvement of SAM accumulation. Finally, SAM2 was overexpressed in ZJU001-GS to give the best SAM-producing recombinant strain ZJU001-GS-SAM2, in which 12.47g/L SAM was produced by following our developed pseudo-exponential fed-batch cultivation strategy, about 81.0% increase comparing to its parent strain ZJU001. The present work laid a solid base for large-scale SAM production with the industrial Saccharomyces cerevisiae strain.

Progress in the microbial production of S-adenosyl-L-methionine

S-Adenosyl-L-methionine (SAM), which exists in all living organisms, serves as an activated group donor in a range of metabolic reactions, including trans-methylation, trans-sulfuration and trans-propylamine. Compared with its chemical synthesis and enzyme catalysis production, the microbial production of SAM is feasible for industrial applications. The current clinical demand for SAM is constantly increasing. Therefore, vast interest exists in engineering the SAM metabolism in cells for increasing product titers. Here, we provided an overview of updates on SAM microbial productivity improvements with an emphasis on various strategies that have been used to enhance SAM production based on increasing the precursor and co-factor availabilities in microbes. These strategies included the sections of SAM-producing microbes and their mutant screening, optimization of the fermentation process, and the metabolic engineering. The SAM-producing strains that were used extensively were Saccharomyces cerevisiae, Pichia pastoris, Candida utilis, Scheffersomyces stipitis, Kluyveromyces lactis, Kluyveromyces marxianus, Corynebacterium glutamicum, and Escherichia coli, in addition to others. The optimization of the fermentation process mainly focused on the enhancement of the methionine, ATP, and other co-factor levels through pulsed feeding as well as the optimization of nitrogen and carbon sources. Various metabolic engineering strategies using precise control of gene expression in engineered strains were also highlighted in the present review. In addition, some prospects on SAM microbial production were discussed.

Comparative performance of S-adenosyl-L-methionine biosynthesis and degradation in Pichia pastoris using different promoters and novel consumption inhibitors

The yeast Pichia pastoris is a widely used host for recombinant protein expression, and has recently been engineered for whole-cell biocatalysis. The inducible P(AOX) and constitutive P(GAP) promoters are commonly employed. In this study, the S-adenosyl-L-methionine (SAM) biosynthesis and degradation efficiency of two P. pastoris strains were compared, and novel inhibitors that suppress SAM degradation were characterized. The strains exhibited clear physiological differences. P(GAP)-Pichia showed higher transcription and activity of SAM synthetase, and the rapid cell growth led to higher levels of spermidine synthesis from SAM. In contrast, P(AOX)-Pichia synthesized higher levels of glutathione from SAM, and this strain responded to hydrogen peroxide formation during methanol utilization. Aristeromycin proved an efficient inhibitor of SAM degradation in P(AOX)-Pichia; 0.02 mg/L led to a 36.36% reduction in the ratio of glutathionine:SAM, and SAM accumulation was enhanced by 7.74% to 11.83 g/L. Ethanol was an even more efficient inhibitor of SAM consumption in P(GAP)-Pichia; 8 g/L resulted in a 73.68% decrease in the ratio of SPD:SAM, and SAM production was elevated by 54.55% to 0.17 g/L/h.

Engineered Pichia pastoris for enhanced production of S-adenosylmethionine

A genetically engineered strain of Pichia pastoris expressing S-adenosylmethionine synthetase gene from Saccharomyces cerevisiae under the control of AOX 1 promoter was developed. Induction of recombinant strain with 1% methanol resulted in the expression of SAM2 protein of ~ 42 kDa, whereas control GS115 showed no such band. Further, the recombinant strain showed 17-fold higher enzyme activity over control. Shake flask cultivation of engineered P. pastoris in BMGY medium supplemented with 1% L-methionine yielded 28 g/L wet cell weight and 0.6 g/L S-adenosylmethionine, whereas control (transformants with vector alone) with similar wet cell weight under identical conditions accumulated 0.018 g/L. The clone cultured in the bioreactor containing enriched methionine medium showed increased WCW (117 g/L) as compared to shake flask cultures and yielded 2.4 g/L S-adenosylmethionine. In spite of expression of SAM 2 gene up to 90 h, S-adenosylmethionine accumulation tended to plateau after 72 h, presumably because of the limited ATP available in the cells at stationery phase. The recombinant P pastoris seems promising as potential source for industrial production of S-adenosylmethionine.

Improved co-production of S-adenosylmethionine and glutathione using citrate as an auxiliary energy substrate

The effects of sodium citrate on the fermentative co-production of S-adenosylmethionine (SAM) and glutathione (GSH) using Candida utilis CCTCC M 209298 were investigated. Sodium citrate was beneficial for the biosynthesis of SAM and GSH and in turn improved intracellular SAM and GSH contents. Adding 2 g/L of sodium citrate at 15 h was the most efficient approach for achieving elevated co-production of SAM and GSH. Using this sodium citrate addition mode, co-production of SAM and GSH reached 663.9 mg/L, which was increased by 27.5% compared to the control. Based on analysis of the kinetic parameters, evaluation of the energy metabolism and assay of key enzymes, sodium citrate was verified to act as an auxiliary energy substrate for the overproduction of SAM and GSH.

Enhancing the production of S-adenosyl-L-methionine in Pichia pastoris GS115 by metabolic engineering

S-adenosyl-L-methionine is an important bioactive molecule participating in a number of biochemical reactions including the transmethylation and transsulphuration reactions of proteins and the biosynthesis of aliphatic polyamines. Strategies of metabolic engineering were used to alter the metabolic flux for enhancing the production of S-adenosyl-L-methionine (SAM) in Pichia pastoris GS115. These strategies include the over-expression of Sam2 by knock-in technique and the disruption of Cbs by knock-out technique. Three strains, ZJGSU1 with knock- in of Sam2, ZJGSU2 with knock-out of Cbs and ZJGSU3 with both knock-in of Sam2 and knock -out of Cbs, were constructed for the effective production of SAM. Yields of SAM in strains ZJGSU1 and ZJGSU2 were 32- and 5-fold higher than in the original strain P. pastoris GS115, respectively. The strain ZJGSU3 had a dramatic increase in the SAM yield, and it was 46-fold higher compared to the original strain. These results indicate that there is a strong synergistic effect on the production of SAM by combining knock-in with knock-out techniques. The yield of SAM in ZJGSU3 strain was 4.37 g/L in a 3 L fermentor. This study provides deep insight into the effective industrial production of SAM in future.

Natural strategies for the spatial optimization of metabolism in synthetic biology

Metabolism is a highly interconnected web of chemical reactions that power life. Though the stoichiometry of metabolism is well understood, the multidimensional aspects of metabolic regulation in time and space remain difficult to define, model and engineer. Complex metabolic conversions can be performed by multiple species working cooperatively and exchanging metabolites via structured networks of organisms and resources. Within cells, metabolism is spatially regulated via sequestration in subcellular compartments and through the assembly of multienzyme complexes. Metabolic engineering and synthetic biology have had success in engineering metabolism in the first and second dimensions, designing linear metabolic pathways and channeling metabolic flux. More recently, engineering of the third dimension has improved output of engineered pathways through isolation and organization of multicell and multienzyme complexes. This review highlights natural and synthetic examples of three-dimensional metabolism both inter- and intracellularly, offering tools and perspectives for biological design.

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.

Co-production of gamma-glutamylcysteine and glutathione by mutant strain Saccharomyces cerevisiae FC-3 and its kinetic analysis

Co-production of gamma -glutamylcysteine (gamma -GC) and glutathione (GSH) by a novel mutant strain Saccharomyces cerevisiae FC-3 and its kinetic analysis were investigated. The strain could produce gamma -GC and GSH with high yields (4.22 and 14.3 mg/g-DCW, respectively) in batch submerged cultures. Effects of medium components and cultivation conditions on cell growth and the contents of intracellular gamma -GC and GSH were examined. Results show that 2% (w/v) sucrose and 2.5% (w/v) yeast extract are the best carbon and nitrogen sources, respectively, and supplement of three amino acids (glycine, cysteine and glutamate), each at 0.08% (w/v), in the medium could enhance gamma -GC and GSH production. In addition, optimal operating conditions are at the initial pH value of 7.0, 30 degrees C and 200 rev/min. Moreover, results obtained from kinetic analyses reveal that gamma -GC production is mixed-type growth associated, but GSH production is growth-associated.

Synthesis of methyl halides from biomass using engineered microbes

Methyl halides are used as agricultural fumigants and are precursor molecules that can be catalytically converted to chemicals and fuels. Plants and microorganisms naturally produce methyl halides, but these organisms produce very low yields or are not amenable to industrial production. A single methyl halide transferase (MHT) enzyme transfers the methyl group from the ubiquitous metabolite S-adenoyl methionine (SAM) to a halide ion. Using a synthetic metagenomic approach, we chemically synthesized all 89 putative MHT genes from plants, fungi, bacteria, and unidentified organisms present in the NCBI sequence database. The set was screened in Escherichia coli to identify the rates of CH(3)Cl, CH(3)Br, and CH(3)I production, with 56% of the library active on chloride, 85% on bromide, and 69% on iodide. Expression of the highest activity MHT and subsequent engineering in Saccharomyces cerevisiae results in productivity of 190 mg/L-h from glucose and sucrose. Using a symbiotic co-culture of the engineered yeast and the cellulolytic bacterium Actinotalea fermentans, we are able to achieve methyl halide production from unprocessed switchgrass (Panicum virgatum), corn stover, sugar cane bagasse, and poplar (Populus sp.). These results demonstrate the potential of producing methyl halides from non-food agricultural resources.