S -Adenosyl- l -methionine production by Saccharomyces cerevisiae SAM 0801 using dl -methionine mixture: From laboratory to pilot scale

Multilevel metabolic engineering for enhanced synthesis of S-adenosylmethionine by Bacillus amyloliquefaciens

OBJECTIVES

To enhance the de novo synthesis of SAM, the effects of several key genes on SAM synthesis were examined based on modular strategy, and the key genes were manipulated to obtain an engineered strain with high SAM production.

RESULTS

In Bacillus amyloliquefaciens HSAM6, the deletion of argG gene to block aspartic acid branching degradation increased SAM titer to 254.78 ± 15.91 mg/L, up 18% from HSAM6. Subsequently, deleting the moaA gene to boost the supply of 5-methyltetrahydrofolate led to the stunted growth and the plummeting yield of SAM. Further improvement of strain growth by overexpression of the citA gene, while SAM synthesis was not significantly enhanced. Finally, the maximum SAM titer (452.89 ± 13.42 mg/L) was obtained by overexpression SAM2 gene using the multicopy plasmid.

CONCLUSIONS

The deletion of argG gene and the overexpression of SAM2 gene significantly improved SAM synthesis in B. amyloliquefaciens.

Breeding of Saccharomyces cerevisiae with a High-Throughput Screening Strategy for Improvement of S-Adenosyl-L-Methionine Production

S-adenosyl-l-methionine (SAM), a vital physiologically active substance in living organisms, is produced by fermentation over Saccharomyces cerevisiae. The main limitation in SAM production was the low biosynthesis ability of SAM in S. cerevisiae. The aim of this work is to breed an SAM-overproducing mutant through UV mutagenesis coupled with high-throughput selection. Firstly, a high-throughput screening method by rapid identification of positive colonies was conducted. White colonies on YND medium were selected as positive strains. Then, nystatin/sinefungin was chosen as a resistant agent in directed mutagenesis. After several cycles of mutagenesis, a stable mutant 616-19-5 was successfully obtained and exhibited higher SAM production (0.41 g/L vs 1.39 g/L). Furthermore, the transcript levels of the genes SAM2, ADO1, and CHO2 involved in SAM biosynthesis increased, while ergosterol biosynthesis genes in mutant 616-19-5 significantly decreased. Finally, building on the above work, S. cerevisiae 616-19-5 could produce 10.92 ± 0.2 g/L SAM in a 5-L fermenter after 96 h of fermentation, showing a 2.02-fold increase in the product yield compared with the parent strain. Paving the way of breeding SAM-overproducing strain has improved the good basis for SAM industrial production.

Genome-scale metabolic model analysis of Pichia pastoris for enhancing the production of S-adenosyl-L-methionine

Komagataella phaffii, formerly Pichia pastoris (P. pastoris), is a promising methylotrophic yeast used in industry to produce recombinant protein and valuable metabolites. In this study, a genome-scale metabolic model (GEMs) was reconstructed and used to assess P. pastoris' metabolic capabilities for the production of S-adenosyl-L-methionine (AdoMet or SAM or SAMe) from individual carbon sources along with the addition of L-methionine. In a model-driven P. pastoris strain, the well-established genome-scale metabolic model iAUKM can be implemented to predict high valuable metabolite production. The model, iAUKM, was created by merging the previously published iMT1026 model and the draught model generated using Raven toolbox from the KEGG database which covered 2309 enzymatic reactions associated with 1033 metabolic genes and 1750 metabolites. The highly curated model was successful in capturing P. pastoris growth on various carbon sources, as well as AdoMet production under various growth conditions. Many overexpression gene targets for increasing AdoMet accumulation in the cell have been predicted for various carbon sources. Inorganic phosphatase (IPP) was one of the predicted overexpression targets as revealed from simulations using iAUKM. When IPP gene was integrated into P. pastoris, we found that AdoMet accumulation increased by 16% and 14% using glucose and glycerol as carbon sources, respectively. Our in silico results shed light on the factors limiting AdoMet production, as well as key pathways for rationalized engineering to increase AdoMet yield.

Enhancement of S-adenosylmethionine production by deleting thrB gene and overexpressing SAM2 gene in Bacillus amyloliquefaciens

OBJECTIVES

To improve the S-adenosylmethionine (SAM) production in methionine-free medium, effects of deleting genes of SAM decarboxylase (speD) and homoserine kinase (thrB) on SAM titers were investigated, and the SAM synthetase gene (SAM2) was also overexpressed.

RESULTS

In B. amyloliquefaciens HSAM2, deleting speD to block the SAM utilization pathway significantly reduced the SAM titer. After knockout of thrB to block the branched pathway, the resulted mutant HSAM4 produced 143.93 mg/L SAM, increasing by 42% than HSAM2. Further plasmid-based expression of SAM2 improved the SAM titer to 226.92 mg/L, and final optimization of key fermentation parameters resulted in the maximum SAM titer of 412.01 mg/L in flasks batch fermentation.

CONCLUSIONS

Deleting thrB and overexpressing SAM2 gene were efficient for enhanced SAM production in B. amyloliquefaciens. The maximum SAM titer in flasks batch fermentation was much higher than that of previous reports.

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.

Metabolic engineering of Bacillus amyloliquefaciens for enhanced production of S-adenosylmethionine by coupling of an engineered S-adenosylmethionine pathway and the tricarboxylic acid cycle

BACKGROUND

S-Adenosylmethionine (SAM) is a critical cofactor involved in many biochemical reactions. However, the low fermentation titer of SAM in methionine-free medium hampers commercial-scale production. The SAM synthesis pathway is specially related to the tricarboxylic acid (TCA) cycle in Bacillus amyloliquefaciens. Therefore, the SAM synthesis pathway was engineered and coupled with the TCA cycle in B. amyloliquefaciens to improve SAM production in methionine-free medium.

RESULTS

Four genes were found to significantly affect SAM production, including SAM2 from Saccharomyces cerevisiae, metA and metB from Escherichia coli, and native mccA. These four genes were combined to engineer the SAM pathway, resulting in a 1.42-fold increase in SAM titer using recombinant strain HSAM1. The engineered SAM pathway was subsequently coupled with the TCA cycle through deletion of succinyl-CoA synthetase gene sucC, and the resulted HSAM2 mutant produced a maximum SAM titer of 107.47 mg/L, representing a 0.59-fold increase over HSAM1. Expression of SAM2 in this strain via a recombinant plasmid resulted in strain HSAM3 that produced 648.99 mg/L SAM following semi-continuous flask batch fermentation, a much higher yield than previously reported for methionine-free medium.

CONCLUSIONS

This study reports an efficient strategy for improving SAM production that can also be applied for generation of SAM cofactors supporting group transfer reactions, which could benefit metabolic engineering, chemical biology and synthetic biology.