Metabolic Engineering of the Shikimate Pathway for Production of Aromatics and Derived Compounds-Present and Future Strain Construction Strategies.

Nils J H Averesch,Jens O Krömer

doi:10.3389/fbioe.2018.00032

Abstract

The aromatic nature of shikimate pathway intermediates gives rise to a wealth of potential bio-replacements for commonly fossil fuel-derived aromatics, as well as naturally produced secondary metabolites. Through metabolic engineering, the abundance of certain intermediates may be increased, while draining flux from other branches off the pathway. Often targets for genetic engineering lie beyond the shikimate pathway, altering flux deep in central metabolism. This has been extensively used to develop microbial production systems for a variety of compounds valuable in chemical industry, including aromatic and non-aromatic acids like muconic acid, para-hydroxybenzoic acid, and para-coumaric acid, as well as aminobenzoic acids and aromatic α-amino acids. Further, many natural products and secondary metabolites that are valuable in food- and pharma-industry are formed outgoing from shikimate pathway intermediates. (Re)construction of such routes has been shown by de novo production of resveratrol, reticuline, opioids, and vanillin. In this review, strain construction strategies are compared across organisms and put into perspective with requirements by industry for commercial viability. Focus is put on enhancing flux to and through shikimate pathway, and engineering strategies are assessed in order to provide a guideline for future optimizations.

Highlights

Importance of Bio-Derived (Aromatic) Building Blocks for the Global Chemical MarketThe worldwide push to move toward a more sustainable society includes the goal to move from fossil fuel dependency toward renewable feedstocks and aims to maintain and increase standards of living by facilitating the access to pharmaceuticals and securing the availability of foodstuff
Aromatic compounds are almost exclusively obtained via the shikimate pathway, which leads to aromatic amino acids and gives rise to diverse aromatic precursors allowing the biosynthesis of a great variety of secondary metabolites/natural products (Knaggs, 2003; Kayser and Averesch, 2015; Lai et al, 2017)
The full spectrum of shikimate pathway derived products is covered; only studies outgoing from non-petrochemistry derived carbon-sources are considered, unlike, e.g., production of ccMA in Pseudomonas putida from benzoate (Schmidt and Knackmuss, 1984; Bang and Choi, 1995; Choi et al, 1997), as benzoate can hardly be considered a sustainable feedstock

Summary

Introduction

Importance of Bio-Derived (Aromatic) Building Blocks for the Global Chemical MarketThe worldwide push to move toward a more sustainable society includes the goal to move from fossil fuel dependency toward renewable feedstocks and aims to maintain and increase standards of living by facilitating the access to pharmaceuticals and securing the availability of foodstuff. Initial de novo production of ccMA in S. cerevisiae was established by following a similar strain construction strategy as in the first approach in E. coli (Draths and Frost, 1994): partial deletion of ARO1 (the aroE analogous domain) blocked the conversion of 3-dehydroshikimate into shikimate, while a DHS dehydratase from Bacillus thuringiensis (aroZ), a PCA decarboxylase from K. pneumoniae (aroY), and a catechol 1,2-dioxygenases from Acinetobacter radioresistens (catA) composed the pathway (Weber et al, 2012).

Results

Conclusion