Engineering the pathway in Escherichia coli for the synthesis of medium-chain-length polyhydroxyalkanoates consisting of both even- and odd-chain monomers

Qianqian Zhuang,Qingsheng Qi

doi:10.1186/s12934-019-1186-x

Abstract

BackgroundMedium-chain-length polyhydroxyalkanoates (mcl-PHAs) containing various chain length monomers from C6 to C14 have more applications besides sustainable and environmental-friendly biomaterials owing to their superior physical and mechanical properties. We engineered a reversed fatty acid β-oxidation pathway in Escherichia coli that can synthesize mcl-PHA directly from glucose and achieved high yield. However, there were only even-chain monomers in the biosynthetic polymers. The need for mcl-PHA harboring both even- and odd-chain monomers with better and wider utility impels us to develop the biosynthetic routes for the production of the novel and unnatural mcl-PHA through rewiring the basic metabolism.ResultsIn the present study, a propionate assimilation and metabolic route was integrated into the reversed fatty acid β-oxidation in order to produce mcl-PHA consisting of both even- and odd-numbered monomers. The content of odd-numbered monomers in mcl-PHA was improved with the increased propionate addition. After further deletion of pyruvate oxidase (PoxB) and pyruvate formate-lyase (PflB), the metabolically engineered chassis E. coli LZ08 harboring pQQ05 and pZQ06 (overexpression of prpP and prpE genes from Ralstonia eutropha H16) innovatively accumulated 6.23 wt% mcl-PHA containing odd-chain monomers ranging from 7 to 13 carbon atoms about 20.03 mol%.ConclusionsThis is the first successful report on production of mcl-PHA harboring both even- and odd-chain monomers (C6–C14) synthesized from glucose and propionate in recombinant E. coli. This present study achieved the highest yield of de novo production of mcl-PHA containing odd-numbered monomers in E. coli at shake-flask fermentation level. Continued engineering of host strains and pathway enzymes will ultimately lead to more economical production of odd-chain monomers based on market demand. The synthetic pathway can provide a promising platform for production of other value-added chemicals and biomaterials that use acetyl-CoA and propionyl-CoA as versatile precursors and can be extended to other microorganisms as intelligent cell factories.

Highlights

Medium-chain-length polyhydroxyalkanoates containing various chain length monomers from C6 to C14 have more applications besides sustainable and environmental-friendly biomaterials owing to their superior physical and mechanical properties
The results demonstrated that the amount of odd-numbered monomers accumulated in the recombinant E. coli depended on the combination of propionate supplementation and propionyl-CoA supply
Glucose leads to the formation of acetyl-CoA through glycolysis for the priming molecule production whereas in the engineered pathway of odd-chain precursor supply, propionate uptake can be promoted by propionate permease (PrpP) according to the previous results [24]

Summary

Introduction

Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) containing various chain length monomers from C6 to C14 have more applications besides sustainable and environmental-friendly biomaterials owing to their superior physical and mechanical properties. Polyhydroxyalkanoates (PHAs), as a class of environmental-friendly biomaterials, are accumulated by a variety of microbes from renewable carbon resources such as sugars [1, 2] They have garnered great attention because of their unparalleled properties similar to elastomers and thermoplastics as potential alternatives for petroleum-based polymers [3, 4]. The Pseudomonas putida KT2442 mutant, KTOY06, accumulated a homopolymer of poly3-hydroxyheptanoate (P3HHp) up to 71 wt% of its cell dry weight (CDW) when heptanoate was added as a single carbon source [8] In another case, 3-hydroxynonanoate (3HN) monomer (30–80 mol%) was the major constituent of polyhydroxyalkanoates accumulated from odd-numbered fatty acids by microorganisms [9]. It is a pressing demand to exploit an efficient metabolic pathway that leads to the formation of corresponding odd-chain (R)-3-hydroxyacyl-CoA as precursors for the acyl-chain elongation to biosynthesize mcl-PHA containing various odd-numbered monomers via adding the inexpensive carbon source-glucose

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