Engineering a heterologous synthetic pathway in Escherichia coli for efficient production of biotin

Bioproduction of methylated phenylpropenes and isoeugenol in Escherichia coli

Phenylpropenes are a class of natural products that are synthesised by a vast range of plant species and hold considerable promise in the flavour and fragrance industries. Many in vitro studies have been carried out to elucidate and characterise the enzymes responsible for the production of these volatile compounds. However, there is a scarcity of studies demonstrating the in vivo production of phenylpropenes in microbial cell factories. In this study, we engineered Escherichia coli to produce methylchavicol, methyleugenol and isoeugenol from their respective phenylacrylic acid precursors. We achieved this by extending and modifying a previously optimised heterologous pathway for the biosynthesis of chavicol and eugenol. We explored the potential of six S-adenosyl l-methionine (SAM)-dependent O-methyltransferases to produce methylchavicol and methyleugenol from chavicol and eugenol, respectively. Additionally, we examined two isoeugenol synthases for the production of isoeugenol from coniferyl acetate. The best-performing strains in this study were able to achieve titres of 13 mg L-1 methylchavicol, 59 mg L-1 methyleugenol and 361 mg L-1 isoeugenol after feeding with their appropriate phenylacrylic acid substrates. We were able to further increase the methyleugenol titre to 117 mg L-1 by supplementation with methionine to facilitate SAM recycling. Moreover, we report the biosynthesis of methylchavicol and methyleugenol from l-tyrosine through pathways involving six and eight enzymatic steps, respectively.

Advances and prospects in microbial production of biotin

Biotin, serving as a coenzyme in carboxylation reactions, is a vital nutrient crucial for the natural growth, development, and overall well-being of both humans and animals. Consequently, biotin is widely utilized in various industries, including feed, food, and pharmaceuticals. Despite its potential advantages, the chemical synthesis of biotin for commercial production encounters environmental and safety challenges. The burgeoning field of synthetic biology now allows for the creation of microbial cell factories producing bio-based products, offering a cost-effective alternative to chemical synthesis for biotin production. This review outlines the pathway and regulatory mechanism involved in biotin biosynthesis. Then, the strategies to enhance biotin production through both traditional chemical mutagenesis and advanced metabolic engineering are discussed. Finally, the article explores the limitations and future prospects of microbial biotin production. This comprehensive review not only discusses strategies for biotin enhancement but also provides in-depth insights into systematic metabolic engineering approaches aimed at boosting biotin production.

Advances in biotin biosynthesis and biotechnological production in microorganisms

Biotin, also known as vitamin H or B7, acts as a crucial cofactor in the central metabolism processes of fatty acids, amino acids, and carbohydrates. Biotin has important applications in food additives, biomedicine, and other fields. While the ability to synthesize biotin de novo is confined to microorganisms and plants, humans and animals require substantial daily intake, primarily through dietary sources and intestinal microflora. Currently, chemical synthesis stands as the primary method for commercial biotin production, although microbial biotin production offers an environmentally sustainable alternative with promising prospects. This review presents a comprehensive overview of the pathways involved in de novo biotin synthesis in various species of microbes and insights into its regulatory and transport systems. Furthermore, diverse strategies are discussed to improve the biotin production here, including mutation breeding, rational metabolic engineering design, artificial genetic modification, and process optimization. The review also presents the potential strategies for addressing current challenges for industrial-scale bioproduction of biotin in the future. This review is very helpful for exploring efficient and sustainable strategies for large-scale biotin production.

Improving Microbial Cell Factory Performance by Engineering SAM Availability

Methylated natural products are widely spread in nature. S-Adenosyl-l-methionine (SAM) is the secondary abundant cofactor and the primary methyl donor, which confer natural products with structural and functional diversification. The increasing demand for SAM-dependent natural products (SdNPs) has motivated the development of microbial cell factories (MCFs) for sustainable and efficient SdNP production. Insufficient and unsustainable SAM availability hinders the improvement of SdNP MCF performance. From the perspective of developing MCF, this review summarized recent understanding of de novo SAM biosynthesis and its regulatory mechanism. SAM is just the methyl mediator but not the original methyl source. Effective and sustainable methyl source supply is critical for efficient SdNP production. We compared and discussed the innate and relatively less explored alternative methyl sources and identified the one involving cheap one-carbon compound as more promising. The SAM biosynthesis is synergistically regulated on multilevels and is tightly connected with ATP and NAD(P)H pools. We also covered the recent advancement of metabolic engineering in improving intracellular SAM availability and SdNP production. Dynamic regulation is a promising strategy to achieve accurate and dynamic fine-tuning of intracellular SAM pool size. Finally, we discussed the design and engineering constraints underlying construction of SAM-responsive genetic circuits and envisioned their future applications in developing SdNP MCFs.