Enhancement of S-adenosylmethionine production by deleting thrB gene and overexpressing SAM2 gene in Bacillus amylolique
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ORIGINAL RESEARCH PAPER
Enhancement of S-adenosylmethionine production by deleting thrB gene and overexpressing SAM2 gene in Bacillus amyloliquefaciens Cong Jiang . Liying Ruan . Xuetuan Wei
. Ailing Guo
Received: 20 November 2019 / Accepted: 16 June 2020 Ó Springer Nature B.V. 2020
Abstract 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.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10529-020-02945-7) contains supplementary material, which is available to authorized users. C. Jiang L. Ruan X. Wei (&) A. Guo (&) Key Laboratory of Environment Correlative Dietology (Ministry of Education), College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China e-mail: [email protected] A. Guo e-mail: [email protected]
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. Keywords S-adenosylmethionine Bacillus amyloliquefaciens Biosynthesis Metabolic engineering
Introduction S-adenosylmethionine (SAM) is an important biologically active substance widely found in organisms. SAM is involved in various biochemical reactions such as transmethylation, transsulfurylation and transamination, and it serves as cofactor for synthesis and metabolism of nucleic acids, proteins and phospholipids in organisms (Fontecave et al. 2004). Previous studies have shown that SAM has good preventive and therapeutic effects on liver disease, arthritis and depression (Cederbaum 2010; Williams et al. 2005). Therefore, development of SAM-related functional foods and pharmaceuticals is of great significance. Methionine, the precursor of SAM is commonly with low availability in cells (Walther et al. 2017). Therefore, previous fermentation methods mainly add
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methionine as the medium substrate, and involved mutation and genetic engineering breeding have been broadly performed (Chu et al. 2013; Ren et al. 2017). However, methionine serving as the substrate is expensive, leading to the high cost of SAM. Several reports have attempted to synthesize SAM using lowcost carbohydrates substrates (Chen et al. 2015a, 2015b; Han et al. 201
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