Coniferyl alcohol, a lignin precursor, stimulates Rhizobium rhizogenes A4 virulence

Developmental changes in lignin composition are driven by both monolignol supply and laccase specificity

The factors controlling lignin composition remain unclear. Catechyl (C)-lignin is a homopolymer of caffeyl alcohol with unique properties as a biomaterial and precursor of industrial chemicals. The lignin synthesized in the seed coat of Cleome hassleriana switches from guaiacyl (G)- to C-lignin at around 12 to 14 days after pollination (DAP), associated with a rerouting of the monolignol pathway. Lack of synthesis of caffeyl alcohol limits C-lignin formation before around 12 DAP, but coniferyl alcohol is still synthesized and highly accumulated after 14 DAP. We propose a model in which, during C-lignin biosynthesis, caffeyl alcohol noncompetitively inhibits oxidation of coniferyl alcohol by cell wall laccases, a process that might limit movement of coniferyl alcohol to the apoplast. Developmental changes in both substrate availability and laccase specificity together account for the metabolic fates of G- and C-monolignols in the Cleome seed coat.

Efficient biosynthesis of cinnamyl alcohol by engineered Escherichia coli overexpressing carboxylic acid reductase in a biphasic system

Background

Cinnamyl alcohol is not only a kind of flavoring agent and fragrance, but also a versatile chemical applied in the production of various compounds. At present, the preparation of cinnamyl alcohol depends on plant extraction and chemical synthesis, which have several drawbacks, including limited scalability, productivity and environmental impact. It is therefore necessary to develop an efficient, green and sustainable biosynthesis method.

Results

Herein, we constructed a recombinant Escherichia coli BLCS coexpressing carboxylic acid reductase from Nocardia iowensis and phosphopantetheine transferase from Bacillus subtilis. The strain could convert cinnamic acid into cinnamyl alcohol without overexpressing alcohol dehydrogenase or aldo–keto reductase. Severe product inhibition was found to be the key limiting factor for cinnamyl alcohol biosynthesis. Thus, a biphasic system was proposed to overcome the inhibition of cinnamyl alcohol via in situ product removal. With the use of a dibutyl phthalate/water biphasic system, not only was product inhibition removed, but also the simultaneous separation and concentration of cinnamyl alcohol was achieved. Up to 17.4 mM cinnamic acid in the aqueous phase was totally reduced to cinnamyl alcohol with a yield of 88.2%, and the synthesized cinnamyl alcohol was concentrated to 37.4 mM in the organic phase. This process also demonstrated robust performance when it was integrated with the production of cinnamic acid from l-phenylalanine.

Conclusion

We developed an efficient one-pot two-step biosynthesis system for cinnamyl alcohol production, which opens up possibilities for the practical biosynthesis of natural cinnamyl alcohol at an industrial scale.

Three steps in one pot: biosynthesis of 4-hydroxycinnamyl alcohols using immobilized whole cells of two genetically engineered Escherichia coli strains

Background

4-Hydroxycinnamyl alcohols are a class of natural plant secondary metabolites that include p-coumaryl alcohol, caffeyl alcohol, coniferyl alcohol and sinapyl alcohol, and have physiological, ecological and biomedical significance. While it is necessary to investigate the biological pathways and economic value of these alcohols, research is hindered because of their limited availability and high cost. Traditionally, these alcohols are obtained by chemical synthesis and plant extraction. However, synthesis by biotransformation with immobilized microorganisms is of great interest because it is environmentally friendly and offers high stability and regenerable cofactors. Therefore, we produced 4-hydroxycinnamyl alcohols using immobilized whole cells of engineered Escherichia coli as the biocatalyst.

Results

In this study, we used the recombinant E. coli strain, M15–4CL1–CCR, expressing the fusion protein 4-coumaric acid: coenzyme A ligase and the cinnamoyl coenzyme A reductase and a recombinant E. coli strain, M15–CAD, expressing cinnamyl alcohol dehydrogenase from Populus tomentosa (P. tomentosa). High performance liquid chromatography and mass spectrometry showed that the immobilized whole cells of the two recombinant E. coli strains could effectively convert the phenylpropanoic acids to their corresponding 4-hydroxycinnamyl alcohols. Further, the optimum buffer pH and the reaction temperature were pH 7.0 and 30 °C. Under these conditions, the molar yield of the p-coumaryl alcohol, the caffeyl alcohol and the coniferyl alcohol was around 58, 24 and 60%, respectively. Moreover, the highly sensitive and selective HPLC–PDA–ESI–MSn method used in this study could be applied to the identification and quantification of these aromatic polymers.

Conclusions

We have developed a dual-cell immobilization system for the production of 4-hydroxycinnamyl alcohols from inexpensive phenylpropanoic acids. This biotransformation method is both simple and environmental-friendly, which is promising for the practical and cost effective synthesis of natural products.Graphical abstract