Apr. 13, 2021
In recent years, the rapid depletion of fossil fuels and the growing demand for aromatic compounds has led to an increasing interest in producing these compounds from plant sources. Lignin monohydrates, units of plant lignin, are important aromatic compounds that can be used to produce a variety of high-value chemicals of commercial importance. They are of great interest as market demand develops. However, most natural monolignans are found in low concentrations in plants and their extraction is limited by plant growth and expensive downstream processing costs. Industrial biosynthesis offers a promising alternative, as it allows the large-scale production of natural monolignols from biological resources.
Cinnamic acid, cinnamaldehyde, and cinnamyl alcohol are important flavor and fragrance chemicals. (E)‐Cinnamic acid is an off white solid. (Z)‐Cinnamic acid has three distinct polymorphic forms. Cinnamic acid is prepared by the Perkin reaction. Cinnamic acid is listed as GRAS (generally recognized as safe) and can be used in food and fragrances. Cinnamic acid is not considered an important odorant, but it serves a precursor for esters with pleasant, long‐lasting aromas.
Cinnamaldehyde is a pale yellow liquid with a warm, sweet, spicy odour and a pungent taste reminiscent of cinnamon. It is also listed at GRAS. It is used as a flavour in bakery goods, confection, beverages, toothpaste etc. It is also used in air fresheners. Cinnamaldehyde has many other uses, eg, animal repellent, plant protection against nematodes, flea repellent, an antimicrobial agent. Cinnamyl alcohol is a colorless crystalline solid with a sweet balsamic odour reminiscent of hyacinth. Cinnamyl alcohol also has a GRAS status. Cinnamyl alcohol and its esters are used in perfumery. It is also used in multicolour printing, animal repellents, and insect.
Here, we report a new, high-yielding biphasic biotransformation for the one-pot two-step biosynthesis of cinnamyl alcohol from cinnamic acid. The recombinant E. coli strain BLCS, coexpressing CAR from Nocardia iowensis (Nicar) and SFP from Bacillus subtilis (BsSFP), catalyzed the one-step reduction of cinnamic acid to cinnamic aldehyde. Cinnamaldehyde was then converted to cinnamyl alcohol by endogenous ADHs and AKRs. Subsequently, cinnamyl alcohol was indicated to cause severe product inhibition on its biosynthesis and a biphasic system was used to overcome this problem via in situ product removal for the first time.
Cinnamyl alcohol (a naturally occurring aromatic alcohol) is the backbone of monolignols. Cinnamyl alcohol is not only used in the food and cosmetic industries due to its sweet pungent smell and taste of cinnamon but also shows good anti-inflammatory and antibacterial activity. In addition, cinnamyl alcohol is a versatile chemical used in the synthesis of various valuable compounds such as cinnamic acid esters (which are flavouring and aromatic agents), flunarizine (used in the treatment of fungal infections), paclitaxel (used in cancer treatment) drugs) and cinnamyl glycosides (for their immune-enhancing properties). Cinnamyl alcohol is also synthesised via the monolignol pathway in plants and biotechnology has been reported for the production of natural cinnamyl alcohol by introducing the plant monolignol pathway into microbial strains.
It was reported that higher concentrations of cinnamyl alcohol (4.8 mM) could be obtained by whole-cell biotransformation through the introduction of Populus hirsutus into the E. coli pathway. However, the current production of cinnamyl alcohol using this strategy is still unsatisfactory, as most of the characterised 4CLs show low activity towards cinnamic acid. Therefore, a novel artificial method was designed to mimic the microbial pathway and recombinant brewer's yeast strains expressing Arabidopsis PAL2 (AtPAL2), carboxylic acid reductase from Arabidopsis Nocardia (NoCAR) and pantotransferase from Pantothenic acid. Escherichia coli (EcSFP) was designed to biotransform 1-phenylalanine to cinnamic alcohol.