Plants represent a vast, renewable resource and are well suited to provide sustainably for humankind’s transportation fuel needs. To produce infrastructure-compatible fuels from biomass, two challenges remain: overcoming plant cell wall recalcitrance to extract sugar and phenolic intermediates, and reduction of oxygenated intermediates to fuel molecules. To compete with fossil-based fuels, two primary routes to deconstruct cell walls are under development, namely biochemical and thermochemical conversion. Here, we focus on overcoming recalcitrance with biochemical conversion, which uses low-severity thermochemical pretreatment followed by enzymatic hydrolysis to produce soluble sugars. Many challenges remain, including understanding how pretreatments affect the physicochemical nature of heterogeneous cell walls; determination of how enzymes deconstruct the cell wall effectively with the aim of designing superior catalysts; and resolution of issues associated with the co-optimization of pretreatment, enzymatic hydrolysis, and fermentation. Here, we highlight some of the scientific challenges and open questions with a particular focus on problems across multiple length scales.

Deconstruction of lignocellulosic biomass to fuels and chemicals

(1985). The Properties of Fungal and Bacterial Cellulases with Comment on their Production and Application. Biotechnology and Genetic Engineering Reviews: Vol. 3, No. 1, pp. 39-110.

https://www.tandfonline.com/doi/pdf/10.1080/02648725.1985.10647809

The Properties of Fungal and Bacterial Cellulases with Comment on their Production and Application

Biodegradation of cellulosic materials: Substrates, microorganisms, enzymes and products

Induction, isolation and testing of stable Trichoderma reesei mutants with improved production of solubilizing cellulase

Lignocellulosic materials containing cellulose, hemicellulose, and lignin as their main constituents are the most abundant renewable organic resource present on Earth The conversion of both cellulose and hemicellulose for production of fuel ethanol is being studied intensively with a view to develop a technically and economically viable bioprocess The fermentation of glucose, the main constituent of cellulose hydrolyzate, to ethanol can be carried out efficiently On the other hand, although bioconversion of xylose, the main pentose sugar obtained on hydrolysis of hemicellulose, to ethanol presents a biochemical challenge, especially if it is present along with glucose, it needs to be fermented to make the biomass-to-ethanol process economical A lot of attention therefore has been focussed on the utilization of both glucose and xylose to ethanol Accordingly, while describing the advancements that have taken place to get xylose converted efficiently to ethanol by xylose-fermenting organisms, the review deals mainly with the strategies that have been put forward for bioconversion of both the sugars to achieve high ethanol concentration, yield, and productivity The approaches, which include the use of (1) xylose-fermenting yeasts alone, (2) xylose isomerase enzyme as well as yeast, (3) immobilized enzymes and cells, and (4) sequential fermentation and co-culture process are described with respect to their underlying concepts and major limitations Genetic improvements in the cultures have been made either to enlarge the range of substrate utilization or to channel metabolic intermediates specifically toward ethanol These contributions represent real significant advancements in the field and have also been adequately dealt with from the point of view of their impact on utilization of both cellulose and hemicellulose sugars to ethanol

K.M.H. Nevalainen

Papers

A high cellulase-producing mutant strain of Trichoderma reesei☆