One-Pot Conversion of Cinnamaldehyde to 2-Phenylethanol via a Biosynthetic Cascade Reaction

Biosynthesis of 2-phenylethanol from styrene using engineered Escherichia coli whole cells

2-Phenylethanol, an aromatic alcohol with a rose scent, is widely used in the cosmetics, food, and pharmaceutical industries. We designed an efficient multi-enzyme cascade pathway for production of 2-phenylethanol from styrene as the substrate. Initially, 2-phenylethanol was produced by overexpression of styrene monooxygenase A (styA), styrene monooxygenase B (styB), styrene oxide isomerase (SOI), alcohol dehydrogenase (yahK), and glucose dehydrogenase (gdh) in Escherichia coli to give 6.28 mM 2-phenylethanol. Subsequently, plasmids with different copy numbers were employed to balance the expression of pathway enzymes to produce 10.28 mM 2-phenylethanol, resulting in a 63.7 % increase in the final yield. Furthermore, the pH and temperature of the whole-cell conversion reaction were optimized, the optimum pH and temperature are 7.5 and 35℃, respectively. Finally, whole-cell conversion experiment was conducted, and the production of 2-phenylethanol reached 48.17 mM within 10 h. This study provides a theoretical and practical foundation for production of 2-phenylethanol.

Biotechnological 2-Phenylethanol Production: Recent Developments

2-Phenylethanol (2-PE) is a key flavor compound with a rose-like scent, used in the cosmetics, perfume, home care and food industries. This aroma compound can be obtained naturally from various flowers, however chemical synthesis is the most used route to meet market demand. The increasing interest in natural products has led to the development of more environmentally friendly alternatives for 2-PE production through biotechnological approaches. The most efficient approach involves the biotransformation of L-phenylalanine into 2-PE via the Ehrlich pathway, a process observed in different microorganisms such as yeasts and bacteria. 2-PE produced by this way can be considered as natural. However, due to the toxicity of the aroma to the producing microorganism, low production yields are typically obtained, motivating efforts to develop production processes that can overcome this bottleneck, enhance 2-PE yields and reduce the production costs. This review presents and discusses the latest advances in the bioproduction of 2-PE through microbial fermentation, in terms of producing strains, the optimization of cultivation processes, strategies to mitigate product toxicity, and the use of low value feedstocks. Novel applications for 2-PE are also highlighted.

Applications of biocatalytic CC bond reductions in the synthesis of flavours and fragrances

Industrial biotechnology and biocatalysis can provide very effective synthetic tools to increase the sustainability of the production of fine chemicals, especially flavour and fragrance (F&F) ingredients, the market demand of which has been constantly increasing in the last years. One of the most important transformations in F&F chemistry is the reduction of CC bonds, typically carried out with metal-catalysed hydrogenations or hydride-based reagents. Its biocatalytic counterpart is a competitive alternative, showcasing a range of advantages such as excellent chemo-, regio- and stereoselectivity, ease of implementation, mild reaction conditions and modest environmental impact. In the present review, the application of biocatalysed alkene reductions (from microbial fermentations with wild-type strains to engineered isolated ene-reductase enzymes) to synthetic processes useful for the F&F industry will be described, highlighting not only the exquisite stereoselectivity achieved, but also the overall improvement when chirality is not involved. Multi-enzymatic cascades involving CC bioreductions are also examined, which allow much greater chemical complexity to be built in one-pot biocatalytic systems.

Exploring the biotechnological potential of Acinetobacter soli ANG344B: A novel bacterium for 2-phenylethanol production

A bacterium, Acinetobacter soli ANG344B, isolated from river water, exhibited an exceptional capacity to produce 2-phenylethanol (2-PE) using L-phenylalanine (L-Phe) as a precursor-a capability typically observed in yeasts rather than bacteria. Bioreactor experiments were conducted to evaluate the production performance, using glucose as the carbon source for cellular growth and L-Phe as the precursor for 2-PE production. Remarkably, A. soli ANG344B achieved a 2-PE concentration of 2.35 ± 0.26 g/L in just 24.5 h of cultivation, exhibiting a global volumetric productivity of 0.10 ± 0.01 g/L.h and a production yield of 0.51 ± 0.01 g2-PE/gL-Phe, a result hitherto reported only for yeasts. These findings position A. soli ANG344B as a highly promising microorganism for 2-PE production. Whole-genome sequencing of A. soli strain ANG344 revealed a genome size of 3.52 Mb with a GC content of 42.7 %. Utilizing the Rapid Annotation using Subsystem Technology (RAST) server, 3418 coding genes were predicted, including genes coding for enzymes previously associated with the metabolic pathway of 2-PE production in other microorganisms, yet unreported in Acinetobacter species. Through gene mapping, 299 subsystems were identified, exhibiting 30 % subsystem coverage. The whole genome sequence data was submitted to NCBI GeneBank with the BioProject ID PRJNA982713. These draft genome data offer significant potential for exploiting the biotechnological capabilities of A. soli strain ANG344 and for conducting further comparative genomic studies.

Efficient whole cell biotransformation of tyrosol from L-tyrosine by engineered Escherichia coli

An engineered Escherichia coli was constructed by co-expressing L-amino acid deaminase, α-keto acid decarboxylase, alcohol dehydrogenase, and glucose dehydrogenase through two plasmids for tyrosol production. The activity of the rate-limiting enzyme L-amino acid deaminase from Cosenzaea myxofaciens (CmAAD) toward tyrosine was improved by structure-guided modification. The enzyme activity of triple mutant CmAAD V438G/K147V/R151E toward tyrosine was ~5.12-fold higher than that of the wild-type CmAAD. Secondly, the plasmid copy numbers and the gene orders were optimized to improve the titer of tyrosol. Finally, the recombinant strain CS-6 transformed 10 mM tyrosine into 9.56 ± 0.64 mM tyrosol at 45 ℃, and the space-time yield reached 0.478 mM·L^-1·h^-1. This study proposes a novel idea for the efficient and natural production of tyrosol, which has great potential for industrial application.

Ene-Reductase: A Multifaceted Biocatalyst in Organic Synthesis

Biocatalysis integrate microbiologists, enzymologists, and organic chemists to access the repertoire of pharmaceutical and agrochemicals with high chemoselectivity, regioselectivity, and enantioselectivity. The saturation of carbon-carbon double bonds by biocatalysts challenges the conventional chemical methodology as it bypasses the use of precious metals (in combination with chiral ligands and molecular hydrogen) or organocatalysts. In this line, Ene-reductases (ERs) from the Old Yellow Enzymes (OYEs) family are found to be a prominent asymmetric biocatalyst that is increasingly used in academia and industries towards unparalleled stereoselective trans-hydrogenations of activated C=C bonds. ERs gained prominence as they were used as individual catalysts, multi-enzyme cascades, and in conjugation with chemical reagents (chemoenzymatic approach). Besides, ERs' participation in the photoelectrochemical and radical-mediated process helps to unlock many scopes outside traditional biocatalysis. These up-and-coming methodologies entice the enzymologists and chemists to explore, expand and harness the chemistries displayed by ERs for industrial settings. Herein, we reviewed the last five year's exploration of organic transformations using ERs.

Enhancement of 2-phenylethanol production by a wild-type Wickerhamomyces anomalus strain isolated from rice wine

2-Phenylethanol (2-PE) is an important high-grade aromatic alcohol, which is widely used in the cosmetics, perfumery and food industries. However, 2-PE is mainly synthesized using a chemical route, which produces environmental pollution and harmful by-products. Screening of high-yielding wild-type strains has become an important goal for the future biosynthesis of 2-PE. In this study, a wild-type Wickerhamomyces anomalus was isolated from rice wine fermented mash. By optimizing the initial glucose and l-phenylalanine concentrations, 2630.7 mg/L of 2-PE was obtained in shaking flasks. The conditions of initial glucose and l-phenylalanine concentration, pH, and inoculation amount were optimized for 2-PE production with W. anomalus. Finally, based on the optimal conditions, the 2-PE titer reached 4,727.3 mg/L by a single-dose fed-batch strategy in a 5-L bioreactor. The results showed that the ability was expanded to harness the Ehrlich pathway for the production of high-value aromatics in aroma-producing yeast species.