Novel Mode Engineering for β-Alanine Production in Escherichia coli with the Guide of Adaptive Laboratory Evolution

Enhancing the Viability of Spray-Dried Limosilactobacillus fermentum Using Quercetin-Integrated Encapsulation: Physicochemical, Metabolic, and Transcriptomic Insights

The application of spray drying for the production of probiotic microcapsules offers many attractive advantages, yet now there are concerns regarding probiotic survivability. This study explores the impact of quercetin (Que) in a whey protein isolate (WPI) and trehalose (TR) encapsulation matrix to improve probiotic survival during spray drying. Results showed that probiotic survival increased by 4.95-fold (p < 0.05) with Que supplementation than the probiotics capsulated using WPI and TR. Physicochemical characteristics analysis indicated that adding Que resulted in slight changes in the moisture and water activity of probiotic microcapsules and improved the gastrointestinal digestion resistance and storage stability. The particle size of the spray-dried microcapsules varied from 9.84 to 11.17 µm. Cell membrane analysis demonstrated that the probiotics encapsulated with the WPI-Que-TR complex exhibited higher integrity and fluidity than WPI-TR-coated probiotics. Moreover, introducing Que reduced the ratio of saturated to unsaturated fatty acids and increased the pyruvate kinase activity of probiotics, contributing to the maintenance of cell activity. Transcriptomic results suggested that Que upregulated genes associated with fatty acid synthesis and energy supply while downregulating certain genes involved in amino acid biosynthesis, enabling probiotics to exist better in harsh conditions. Therefore, those results indicated that the co-microencapsulation of probiotics and hydrophobic active substance-Que-was realized, and the mechanism by which Que affects probiotic activity during spray drying has been revealed, which provides a scientific foundation for co-encapsulating probiotics with hydrophobic actives. PRACTICAL APPLICATION: In a rapidly growing market, the demand for dry probiotics has surged, highlighting the need for mass production. Spray drying, with its low energy costs and sustainable process, is a promising method for microencapsulating bacteria in protective substrates, enhancing their resistance during storage, processing, and digestion. Que can improve the survival rate of probiotics during spray drying, offering a novel approach for incorporating flavonoids in the creation of probiotic microcapsules with activity and stability.

One-Pot Synthesis of β-Alanine from Fumaric Acid via an Efficient Dual-Enzyme Cascade Biotransformation

As the only naturally occurring β-amino acid, β-alanine has important application prospects in many fields. Driven by the huge demand, biosynthesis is becoming more and more popular as a potential alternative to the chemical synthesis of β-alanine. Although the direct pathway from L-aspartic acid to β-alanine, catalyzed by L-aspartic acid-α-decarboxylase (PanD), is ideal for β-alanine synthesis, it is hindered by the high cost of the substrate and limited economic viability. In this work, a cell-free dual enzyme cascade system based on methylaspartate lyase (EcMAL) and panD was constructed to safely and efficiently synthesize β-alanine using fumarate as a substrate. Taking the previously engineered EcMAL as the target, CgPanD was finally screened as the best candidate through gene mining, sequence alignment, and enzyme property analysis. Finally, under the optimal conditions of 35 °C, pH 8.0, and EcMAL: CgPanD concentration ratio of 1:5, the yield of β-alanine reached 80% theoretical yield within 120 min. This study provides a potential strategy for the biosynthesis of β-alanine, paving the way for future industrial-scale production.

Fine and combinatorial regulation of key metabolic pathway for enhanced β-alanine biosynthesis with non-inducible Escherichia coli

β-Alanine is the only β-amino acid in nature and one of the most important three-carbon chemicals. This work was aimed to construct a non-inducible β-alanine producer with enhanced metabolic flux towards β-alanine biosynthesis in Escherichia coli. First of all, the assembled E. coli endogenous promoters and 5'-untranslated regions (PUTR) were screened to finely regulate the combinatorial expression of genes panDBS and aspBCG for an optimal flux match between two key pathways. Subsequently, additional copies of key genes (panDBS K104S and ppc) were chromosomally introduced into the host A1. On these bases, dynamical regulation of the gene thrA was performed to reduce the carbon flux directed in the competitive pathway. Finally, the β-alanine titer reached 10.25 g/L by strain A14-R15, 361.7% higher than that of the original strain. Under fed-batch fermentation in a 5-L fermentor, a titer of 57.13 g/L β-alanine was achieved at 80 h. This is the highest titer of β-alanine production ever reported using non-inducible engineered E. coli. This metabolic modification strategy for optimal carbon flux distribution developed in this work could also be used for the production of various metabolic products.

Biotechnological production of omega-3 fatty acids: current status and future perspectives

Omega-3 fatty acids, including alpha-linolenic acids (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), have shown major health benefits, but the human body's inability to synthesize them has led to the necessity of dietary intake of the products. The omega-3 fatty acid market has grown significantly, with a global market from an estimated USD 2.10 billion in 2020 to a predicted nearly USD 3.61 billion in 2028. However, obtaining a sufficient supply of high-quality and stable omega-3 fatty acids can be challenging. Currently, fish oil serves as the primary source of omega-3 fatty acids in the market, but it has several drawbacks, including high cost, inconsistent product quality, and major uncertainties in its sustainability and ecological impact. Other significant sources of omega-3 fatty acids include plants and microalgae fermentation, but they face similar challenges in reducing manufacturing costs and improving product quality and sustainability. With the advances in synthetic biology, biotechnological production of omega-3 fatty acids via engineered microbial cell factories still offers the best solution to provide a more stable, sustainable, and affordable source of omega-3 fatty acids by overcoming the major issues associated with conventional sources. This review summarizes the current status, key challenges, and future perspectives for the biotechnological production of major omega-3 fatty acids.

Advances in the synthesis of β-alanine

β-Alanine is the only naturally occurring β-type amino acid in nature, and it is also one of the very promising three-carbon platform compounds that can be applied in cosmetics and food additives and as a precursor in the chemical, pharmaceutical and material fields, with very broad market prospects. β-Alanine can be synthesized through chemical and biological methods. The chemical synthesis method is relatively well developed, but the reaction conditions are extreme, requiring high temperature and pressure and strongly acidic and alkaline conditions; moreover, there are many byproducts that require high energy consumption. Biological methods have the advantages of product specificity, mild conditions, and simple processes, making them more promising production methods for β-alanine. This paper provides a systematic review of the chemical and biological synthesis pathways, synthesis mechanisms, key synthetic enzymes and factors influencing β-alanine, with a view to providing a reference for the development of a highly efficient and green production process for β-alanine and its industrialization, as well as providing a basis for further innovations in the synthesis of β-alanine.

Screening and identification of genes involved in β-alanine biosynthesis in Bacillus subtilis

β-alanine is the only naturally occurring β-amino acid, which is widely used in medicine, food, and feed fields, and generally produced through synthetic biological methods based on engineered strains of Escherichia coli or Corynebacterium glutamicum. However, the β-alanine biosynthesis in Bacillus subtilis, a traditional industrial model microorganism of food safety grade, has not been thoroughly explored. In this study, the native l-aspartate-α-decarboxylase was overexpressed in B. subtilis 168 to obtain an increase of 842% in β-alanine production. A total of 16 single-gene knockout strains were constructed to block the competitive consumption pathways to identify a total of 6 genes (i.e., ptsG, fbp, ydaP, yhfS, mmgA, and pckA) involved in β-alanine synthesis, while the multigene knockout of these 6 genes obtained an increased β-alanine production by 40.1%. Ten single-gene suppression strains with the competitive metabolic pathways inhibited revealed that the inhibited expressions of genes glmS, accB, and accA enhanced the β-alanine production. The introduction of heterologous phosphoenolpyruvate carboxylase increased the β-alanine production by 81.7%, which was 17-fold higher than that of the original strain. This was the first study using multiple molecular strategies to investigate the biosynthetic pathway of β-alanine in B. subtilis and to identify the genetic factors limiting the excessive synthesis of β-alanine by microorganisms.

Embracing a low-carbon future by the production and marketing of C1 gas protein

Food scarcity and environmental deterioration are two major problems that human populations currently face. Fortunately, the disruptive innovation of raw food materials has been stimulated by the rapid evolution of biomanufacturing. Therefore, it is expected that the new trends in technology will not only alter the natural resource-dependent food production systems and the traditional way of life but also reduce and assimilate the greenhouse gases released into the atmosphere. This review article summarizes the metabolic pathways associated with C1 gas conversion and the production of single-cell protein for animal feed. Moreover, the protein function, worldwide authorization, market access, and methods to overcome challenges in C1 gas assimilation microbial cell factory construction are also provided. With widespread attention and increasing policy support, the production of C1 gas protein will bring more opportunities and make tremendous contributions to our sustainable future.

Fatty acid feedstocks enable a highly efficient glyoxylate-TCA cycle for high-yield production of β-alanine

Metabolic engineering to produce tricarboxylic acid (TCA) cycle-derived chemicals is usually associated with problems of low production yield and impaired cellular metabolism. In this work, we found that fatty acid (FA) feedstocks could enable high-yield production of TCA cycle-derived chemicals, while maintaining an efficient and balanced metabolic flux of the glyoxylate-TCA cycle, which is favorable for both product synthesis and cell growth. Here, we designed a novel synthetic pathway for production of β-alanine, an important TCA cycle-derived product, from FAs with a high theortecial yield of 1.391 g/g. By introducing panD, improving aspA, and knocking out iclR, glyoxylate shunt was highly activated in FAs and the yield of β-alanine reached 0.71 g/g from FAs, much higher than from glucose. Blocking the TCA cycle at icd/sucA/fumAC nodes could increase β-alanine yield in a flask cultivation, but severely reduced cell growth and FA utilization during fed-batch processes. Replenishing oxaloacetate by knocking out aspC and recovering fumAC could restore the growth and lead to a titer of 35.57 g/l. After relieving the oxidative stress caused by FA metabolism, β-alanine production could reach 72.05 g/l with a maximum yield of 1.24 g/g, about 86% of the theoretical yield. Our study thus provides a promising strategy for the production of TCA cycle-derived chemicals.

Enhancement of β-Alanine Biosynthesis in Escherichia coli Based on Multivariate Modular Metabolic Engineering

β-alanine is widely used as an intermediate in industrial production. However, the low production of microbial cell factories limits its further application. Here, to improve the biosynthesis production of β-alanine in Escherichia coli, multivariate modular metabolic engineering was recruited to manipulate the β-alanine biosynthesis pathway through keeping the balance of metabolic flux among the whole metabolic network. The β-alanine biosynthesis pathway was separated into three modules: the β-alanine biosynthesis module, TCA module, and glycolysis module. Global regulation was performed throughout the entire β-alanine biosynthesis pathway rationally and systematically by optimizing metabolic flux, overcoming metabolic bottlenecks and weakening branch pathways. As a result, metabolic flux was channeled in the direction of β-alanine biosynthesis without huge metabolic burden, and 37.9 g/L β-alanine was generated by engineered Escherichia coli strain B0016-07 in fed-batch fermentation. This study was meaningful to the synthetic biology of β-alanine industrial production.