Approaches for More Efficient Biological Conversion of Lignocellulosic Feedstocks to Biofuels and Bioproducts

Abstract

The future bioeconomy promises drop-in or performance-advantaged biofuels and bioproducts derived from lignocellulosic biomass, substantial greenhouse gas (GHG) emissions reductions in sectors with few or no alternatives, and increased domestic energy production in countries with sufficient biomass resources. Despite the slower than anticipated pace of commercializing next-generation biofuels, the research community continues to make dramatic improvements at every stage of production, from feedstock cultivation through conversion to final products. However, the interdisciplinary nature of bioenergy research, and the need for crosscoordination among biologists, chemists, agronomists, and engineers, make coordinating and optimizing these strategies challenging. This Perspective surveys recent advancements in bioenergy crop engineering, lignocellulosic biomass deconstruction and fractionation, catabolism of biomass-derived sugars and aromatics, and biological conversion to fuels and products. We organize major research approaches into broad categories and comment on which strategies offer synergies or trade-offs in the context of four approaches to improving the economics and carbon-efficiency of advanced biofuels and bioproducts: 1) maximize sugar conversion to a single product, 2) utilize diverse carbon sources for producing a single product, 3) convert lignin to high-value products, and 4) fractionate the hydrolysate to derive maximum value from each component.

Biotransformation of D-xylose to D-xylonic acid coupled to medium chain length polyhydroxyalkanoate production in cellobiose-grownPseudomonas putidaEM42

“…These optimisation efforts will be the subject of our further work. In any case, bioprocesses based on microbial hosts capable of parallel production of two or more VAC from cheap abundant substrates are drawing considerable attention (Dumon et al ., 2012; Li et al ., 2017; Larroude et al ., 2018; Baral et al ., 2019; Wang et al ., 2019). We argue that the strategy shown here on example of recombinant P. putida EM42 expressing cytoplasmic β-glucosidase represents a promising route for valorisation of (hemi)cellulosic residues and an alternative to the xylonate and mcl-PHA bioproductions reported thus far.…”

“…Economics of these bioprocesses is regrettably still often unsatisfactory but can be significantly improved by parallel valorisation of two or more lignocellulosic substrates. This is allowed by co-streaming of carbon from several sources into a single valued compound or by simultaneous production of two or more VAC (Dumon et al ., 2012; Li et al ., 2017; Larroude et al ., 2018; Baral et al ., 2019; Wang et al ., 2019). Co-production of extracellular and intracellular biochemicals is desirable for facilitated downstream processing (Wang et al , 2019).…”

The Future of Biofuels in an Electrifying Global Transportation Sector: Imperative, Prospects and Challenges

“…Additionally, a key challenge and one of the most expensive unit operations in the process of cellulosic biofuel production is the deconstruction of the biomass through pre-treatment to lignin, fermentable sugars, and other products. Research continues to make advances in tailoring biomass feedstocks for efficient conversion to biofuels and bioproducts, reducing lignin content of the feedstock while increasing sugar and developing processes for converting the lignin to fuel and high value bioproducts (Jung and Altpeter 2016;Baral et al 2019). Bioengineering techniques are also being developed to increase the oil (lipid) content of plants such as sugarcane and sorghum which will make it easier to extract fuel without costly deconstruction of the lignin (Kumar, Long, and Singh 2018).…”

Strategies for the production of biochemicals in bioenergy crops

“…For biological conversion of plant biomass hydrolysates, robust engineered microbial strains are required to allow efficient production of the desired chemicals at high yields, titers, and rates using complex mixtures of low-molecular weight monomers as substrates. Moreover, achieving higher plant biomass yields at reduced cost and enabling efficient deconstruction of the recalcitrant lignocellulosic material represent two other important milestones towards the cost-effectiveness of biochemical production [2,3].…”