Synthesis of Diverse Hydroxycinnamoyl Phenylethanoid Esters Using Escherichia coli

Yeast Metabolic Engineering for Biosynthesis of Caffeic Acid-Derived Phenethyl Ester and Phenethyl Amide

Caffeic acid (CA)-derived phenethyl ester (CAPE) and phenethyl amide (CAPA) are extensively investigated bioactive compounds with therapeutic applications such as antioxidant, anti-inflammatory, and anticarcinogenic properties. To construct microbial cell factories for production of CAPE or CAPA is a promising option given the limitation of natural sources for product extraction and the environmental toxicity of the agents used in chemical synthesis. We reported the successful biosynthesis of caffeic acid in yeast previously. Here in this work, we further constructed the downstream synthetic pathways in yeast for biosynthesis of CAPE and CAPA. After combinatorial engineering of yeast chassis based on the rational pathway engineering method and library-based SCRaMbLE method, we finally obtained the optimal strains that respectively produced 417 μg/L CAPE and 1081 μg/L CAPA. Two screened gene targets of ΔHAM1 and ΔYJL028W were discovered to help improve the product synthesis capacity. This is the first report of the de novo synthesis of CAPA from glucose in an engineered yeast chassis. Future work on enzyme and chassis engineering will further support improving the microbial cell factories for the production of CA derivatives.

Genome-wide analysis reveals Hsf1 maintains high transcript abundance of target genes controlled by strong constitutive promoter in Saccharomyces cerevisiae

BACKGROUND

In synthetic biology, the strength of promoter elements is the basis for precise regulation of target gene transcription levels, which in turn increases the yield of the target product. However, the results of many researches proved that excessive transcription levels of target genes actually reduced the yield of the target product. This phenomenon has been found in studies using different microorganisms as chassis cells, thus, it becomes a bottleneck problem to improve the yield of the target product.

RESULTS

In this study, promoters PGK1p and TDH3p with different strengths were used to regulate the transcription level of alcohol acetyl transferase encoding gene ATF1. The results demonstrated that the strong promoter TDH3p decreased the production of ethyl acetate. The results of Real-time PCR proved that the transcription level of ATF1 decreased rapidly under the control of TDH3p, and the unfolded protein reaction was activated, which may be the reason for the abnormal production caused by the strong promoter. RNA-sequencing analysis showed that the overexpression of differential gene HSP30 increased the transcriptional abundance of ATF1 gene and production of ethyl acetate. Interestingly, deletion of the heat shock protein family (e.g., Hsp26, Hsp78, Hsp82) decreased the production of ethyl acetate, suggesting that the Hsp family was also involved in the regulation of ATF1 gene transcription. Furthermore, the results proved that the Hsf1, an upstream transcription factor of Hsps, had a positive effect on alleviating the unfolded protein response and that overexpression of Hsf1 reprogramed the pattern of ATF1 gene transcript levels. The combined overexpression of Hsf1 and Hsps further increased the production of ethyl acetate. In addition, kinase Rim15 may be involved in this regulatory pathway. Finally, the regulation effect of Hsf1 on recombinant strains constructed by other promoters was verified, which confirmed the universality of the strategy.

CONCLUSIONS

Our results elucidated the mechanism by which Rim15-Hsf1-Hsps pathway reconstructed the repression of high transcription level stress and increased the production of target products, thereby providing new insights and application strategies for the construction of recombinant strains in synthetic biology.

Synthesis of chlorogenic acid and p-coumaroyl shikimate by expressing shikimate gene modules in Escherichia coli

AIM

Chlorogenic acid and p-coumaroyl shikimate are hydroxycinnamic acid derivatives. These compounds are nutraceutical supplements due to their biological activities including prevention of cardiovascular disease and cancers. These two compounds were synthesized in Escherichia coli through two-culture system using two mutants, which are biochemically interdependent. The aim of this work was to improve the titres of their production in a single E. coli mutant in which all necessary genes were introduced. This was done by testing various shikimate gene combinations to determine the optimal gene combination for the synthesis of chlorogenic acid and p-coumaroyl shikimate.

METHODS AND RESULTS

A series of gene modules harbouring shikimate pathway genes were constructs. Six gene module constructs for chlorogenic acid synthesis and eight constructs for p-coumaric acid synthesis were tested in order to find the best one. Chlorogenic acid synthesis showed highest with the gene module construct containing ydiB, aroB, aroG^f , ppsA and tktA. Using the E. coli strain, 109.7 mg L^-1 chlorogenic acid was synthesized. The best gene module construct for the p-coumaroyl shikimate synthesis contained aroD and aroG^f . In addition, we used two E. coli deletion mutant strains (ΔaroK and ΔaroL) to increase the final titre. The E. coli ΔaroK mutant harbouring this gene module construct synthesized 713.4 mg L^-1 of p-coumaroyl shikimate.

CONCLUSION

The chlorogenic acid synthesis using the current system was approximately 35.4% higher of the titre than titres obtained with an alternative method that depends on co-cultivation of two mutants. At the same time, production of p-coumaroyl shikimate increased 5.8 times.

SIGNIFICANCE AND IMPACT OF THE STUDY

The current study's findings indicate that our selection of the shikimate gene module contributed to increases in the levels of the substrates and could be applied to synthesize other compounds whose synthesis requires intermediates of the shikimate pathway.

Towards renewable flavors, fragrances, and beyond

Esters constitute a large space of unique molecules with broad range of applications as flavors, fragrances, pharmaceuticals, cosmetics, green solvents, and advanced biofuels. Global demand of natural esters in food, household cleaner, personal care, and perfume industries is increasing while the ester supply from natural sources has been limited. Development of novel microbial cell factories for ester production from renewable feedstocks can potentially provide an alternative and sustainable source of natural esters and hence help fulfill growing demand. Here, we highlight recent advances in microbial production of esters and provide perspectives for improving its economic feasibility. As the field matures, microbial ester production platforms will enable renewable and sustainable production of flavors and fragrances, and open new market opportunities beyond what nature can offer.

The Pathway Less Traveled: Engineering Biosynthesis of Nonstandard Functional Groups

The field of metabolic engineering has achieved biochemical routes for conversion of renewable inputs to structurally diverse chemicals, but these products contain a limited number of chemical functional groups. In this review, we provide an overview of the progression of uncommon or 'nonstandard' functional groups from the elucidation of their biosynthetic machinery to the pathway optimization framework of metabolic engineering. We highlight exemplary efforts from primarily the last 5 years for biosynthesis of aldehyde, ester, terminal alkyne, terminal alkene, fluoro, epoxide, nitro, nitroso, nitrile, and hydrazine functional groups. These representative nonstandard functional groups vary in development stage and showcase the pipeline of chemical diversity that could soon appear within customized, biologically produced molecules.