Engineering microbial pathways for production of bio-based chemicals from lignocellulosic sugars: current status and perspectives

Jean Marie Francois,Nicolas Morin,Ceren Alkim

doi:10.1186/s13068-020-01744-6

Abstract

Lignocellulose is the most abundant biomass on earth with an annual production of about 2 × 1011 tons. It is an inedible renewable carbonaceous resource that is very rich in pentose and hexose sugars. The ability of microorganisms to use lignocellulosic sugars can be exploited for the production of biofuels and chemicals, and their concurrent biotechnological processes could advantageously replace petrochemicals’ processes in a medium to long term, sustaining the emerging of a new economy based on bio-based products from renewable carbon sources. One of the major issues to reach this objective is to rewire the microbial metabolism to optimally configure conversion of these lignocellulosic-derived sugars into bio-based products in a sustainable and competitive manner. Systems’ metabolic engineering encompassing synthetic biology and evolutionary engineering appears to be the most promising scientific and technological approaches to meet this challenge. In this review, we examine the most recent advances and strategies to redesign natural and to implement non-natural pathways in microbial metabolic framework for the assimilation and conversion of pentose and hexose sugars derived from lignocellulosic material into industrial relevant chemical compounds leading to maximal yield, titer and productivity. These include glycolic, glutaric, mesaconic and 3,4-dihydroxybutyric acid as organic acids, monoethylene glycol, 1,4-butanediol and 1,2,4-butanetriol, as alcohols. We also discuss the big challenges that still remain to enable microbial processes to become industrially attractive and economically profitable.

Highlights

The 21st century is challenging the human society with major social and economic issues owing to the irreversible global warming and the steady rise of environmental pollution, both events mainly resulting from our slave reliance on fossil resources
For high-volume, low-priced chemicals such as those considered here, the higher these three performance indices are, the more competitive biotechnological processes become compared to petrochemical processes
Even though many microorganisms on earth are able to assimilate pentose and hexose sugars, their carbon metabolism is not optimally fashioned to achieve these performances. This necessitates to rewire their actual metabolic network, to plug pathways that exist in other organisms or to create new ones, while ensuring cellular homoeostasis

Summary

Introduction

The 21st century is challenging the human society with major social and economic issues owing to the irreversible global warming and the steady rise of environmental pollution, both events mainly resulting from our slave reliance on fossil resources. A likely reason for low yield and titer of glutaric acid may be found in the promiscuity activity of the a-ketoacid decarboxylase encoded by Lactococcus lactis kivD as this enzyme can readily decarboxylate upstream intermediates of the pathway, namely 2-keto-3-deoxy-d-xylonate and DOP (see below).

Results

Conclusion