Biogenic amines (BAs) have been reported to threaten the Douchi safety, while the BAs formation mechanism and corresponding control method have not been clarified for Douchi. The present study aims to investigate the microbial contribution to BAs in Douchi, and to find the beneficial strain for BAs control. Firstly, the BAs profiles of 15 Douchi samples were analyzed, and common 6 kinds of BAs were detected from different samples. All the samples showed the total BAs contents within the safe dosage range, while the histamine concentrations in 2 samples and β-phenethylamine in 6 samples were above the toxic level. Then, the bacterial and fungal communities were investigated by high-throughput sequencing analysis, and Bacillus and Candida were identified as the dominant bacteria and fungi genus, respectively. Furthermore, nineteen strains were selected from the dominant species of Douchi samples, including 14 Bacillus strains, 2 Staphylococcus strains, 1 Enterococcus strain and 2 Candida strains, and their BAs formation and degradation abilities were evaluated. B. subtilis HB-1 and S. pasteuri JX-2 showed no BAs producing ability, and B. subtilis GD-4 and Candida sp. JX-3 exhibited high BAs degradation ability. Finally, fermented soybean model analysis further verified that B. subtilis HB-1 and S. pasteuri JX-2 could significantly reduce BAs. This study not only contributed to understanding the BAs formation mechanism in Douchi, but also provided potential candidates to control the BAs in fermented soybean products.
Spermidine, a natural autophagy inducer, has a variety of health effects, such as antitumor, antiaging, anti‐inflammation, cardiovascular protection, and neuromodulation. It has been a hot topic in the field of food processing, and current research findings suggest that spermidine‐rich foods may be used in intervention and prevention of age‐related diseases. In this article, recent findings on the safety, health effects, absorption and metabolism of spermidine were reviewed, and advances in food processing, including the raw materials evaluation, physical and chemical processing, and biological processing of spermidine, were highlighted. In particular, the core metabolic pathways, key gene targets, and efficient metabolic engineering strategies involved in the biosynthesis of spermidine and its precursors were discussed. Moreover, limitations and future perspectives of spermidine research were proposed. The purpose of this review is to provide new insights on spermidine from its safety to its food processing, which will advance the commercial production and applications of spermidine‐rich foods and nutraceuticals.
Putrescine is an important C4 platform chemical with extensive applications in bioplastics, pharmaceuticals, and agrochemicals. In this study, multilevel metabolic engineering of Bacillus amyloliquefaciens was performed to achieve the sustainable production of putrescine from biomass hydrolysates rich in glucose and xylose. First, the ornithine decarboxylase pathway was reconstructed in B. amyloliquefaciens by introducing an ornithine decarboxylase from Escherichia coli, resulting in the efficient transformation of ornithine to putrescine. The overall putrescine synthesis process was then recast into three modules including ornithine synthesis module, NADPH synthesis module, and ATP supply module. In the ornithine synthesis module, deletion of ornithine carbamoyltransferase gene argF and arginine repressor gene ahrC, and overexpression of N-acetylglutamate synthase gene argA significantly enhanced putrescine production. Using a cofactor engineering strategy, overexpression of glucose-6P dehydrogenase gene zwf and pyruvate kinase gene pyK proved optimal for putrescine production through NADPH synthesis and ATP supply modules, respectively. Finally, all beneficial genetic manipulations were combined in recombinant strain HZ/CFKΔFC/pHY-argA, and its putrescine titer (5.51 g/L), productivity (0.11 g/(L h)) and yield (0.14 g/g) from xylose were much higher than that previously reported using xylose substrate. Using hydrolysates of Miscanthus f loridulus, higher putrescine titer (6.76 g/L), productivity (0.14 g/ (L h)) and carbohydrate yield (0.17 g/g) were achieved. Thus, multilevel metabolic engineering strategies, including pathway reconstruction, modular engineering, and cofactor engineering, were effective for improving putrescine production. This study describes a proof of concept demonstration of multilevel metabolic engineering of B. amyloliquefaciens for putrescine production from sustainable biomass hydrolysates.
Spermidine is a biologically active polyamine with extensive application potential in functional foods. However, previously reported spermidine titers by biosynthesis methods are relatively low, which hinders its industrial application. To improve the spermidine titer, key genes affecting the spermidine production were mined to modify Bacillus amyloliquefaciens. Genes of Sadenosylmethionine decarboxylase (speD) and spermidine synthase (speE) from different microorganisms were expressed and compared in B. amyloliquefaciens. Therein, the speD from Escherichia coli and speE from Saccharomyces cerevisiae were confirmed to be optimal for spermidine synthesis, respectively. Gene and amino acid sequence analysis further confirmed the function of speD and speE. Then, these two genes were co-expressed to generate a recombinant strain B. amyloliquefaciens HSAM2(PDspeD-SspeE) with a spermidine titer of 105.2 mg/L, improving by 11.0-fold compared with the control (HSAM2). Through optimization of the fermentation medium, the spermidine titer was increased to 227.4 mg/L, which was the highest titer among present reports. Moreover, the consumption of the substrate S-adenosylmethionine was consistent with the accumulation of spermidine, which contributed to understanding its synthesis pattern. In conclusion, two critical genes for spermidine synthesis were obtained, and an engineering B. amyloliquefaciens strain was constructed for enhanced spermidine production.
Background: Spermidine is a biologically active polyamine with extensive application potential in foods and pharmaceuticals. However, previously reported spermidine titers by biosynthesis methods are relatively low, which hinders the industrial fermentation of spermidine. To improve the spermidine titer, key genes affecting the spermidine production were mined to engineer the Bacillus amyloliquefaciens.Results: Genes of S-adenosylmethionine decarboxylase (speD) and spermidine synthase (speE) from different microorganisms were expressed and compared in B. amyloliquefaciens. Therein, the speD from Escherichia coli and speE from Saccharomyces cerevisiae were confirmed to be optimal for spermidine synthesis, respectively. Then, these two genes were co-expressed to generate an engineering strain B. amyloliquefaciens HSAM2(PDspeD-SspeE) with a spermidine titer of 91.31 mg/L, improving by 10.90-fold compared with the control (HSAM2). Through further optimization of fermentation medium, the spermidine titer was increased to 227.35 mg/L, which was the highest titer among present reports. Moreover, the consumption of the substrate S-adenosylmethionine was consistent with the accumulation of spermidine, which contributed to understanding the synthetic pattern of spermidine. Conclusions: Two critical genes for spermidine synthesis were obtained, and an B. amyloliquefaciens cell factory was constructed for enhanced spermidine production, which laid the foundation for further industrial production of spermidine.
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