Integrated engineering of enzymes and microorganisms for improving the efficiency of industrial lignocellulose deconstruction

Abstract

Bioconversion of lignocellulosic biomass to fuels and chemicals represents a new manufacturing paradigm that can help address society's energy, resource, and environmental problems. However, the low efficiency and high cost of lignocellulolytic enzymes currently used hinder their use in the industrial deconstruction of lignocellulose. To overcome these challenges, research efforts have focused on engineering the properties, synergy, and production of lignocellulolytic enzymes. First, lignocellulolytic enzymes' catalytic efficiency, stability, and tolerance to inhibitory compounds have been improved through enzyme mining and engineering. Second, synergistic actions between different enzyme components have been strengthened to construct customized enzyme cocktails for the degradation of specific lignocellulosic substrates. Third, biological processes for protein synthesis and cell morphogenesis in microorganisms have been engineered to achieve a high level and low-cost production of lignocellulolytic enzymes. In this review, the relevant progresses and challenges in these fields are summarized. Integrated engineering is proposed to be essential to achieve cost-effective enzymatic deconstruction of lignocellulose in the future.

Keywords: Biorefinery; Cellulase; Fungi; Genetic engineering; Hemicellulase; Lignocellulose.

Fig. 1

Bioengineering approaches for the development of cost-effective lignocellulolytic enzymes. The Design-Build-Test-Learn cycle (Nielsen and Keasling, 2016) can be used in multiple levels of engineering in this respect.

Fig. 2

Different forms of cellulolytic enzyme systems in microorganisms. OM, outer membrane; IM, inner cytoplasmic membrane; CBD, cellulose-binding domain. The mechanisms of cellulose degradation were reported in references (Brunecky et al., 2013, Eibinger et al., 2020, Liu et al., 2011, Resch et al., 2013).

Fig. 3

Combination of discovery and engineering approaches to improve the performance of lignocellulolytic enzymes.

Fig. 4

Engineering of filamentous fungi for the production of lignocellulolytic enzymes. (A) Selected milestones in strain improvement of T. reesei (Bischof et al., 2016, Allen et al., 2009, Montenecourt and Eveleigh, 1977, Montenecourt and Eveleigh, 1979, Shoemaker et al., 1983, Penttila et al., 1987, Ilmen et al., 1996, Stricker et al., 2006, Merino and Cherry, 2007, Martinez et al., 2008, Herpoel-Gimbert et al., 2008, Seidl et al., 2009, Derntl et al., 2013, Lv et al., 2015, Liu et al., 2015, Chen et al., 2020, Fonseca et al., 2020). For most achievements, the years of corresponding publications are shown. CCR, carbon catabolite repression. (B) Rewiring the cellular networks for cost-effective production of optimized lignocellulolytic enzymes. COS, cello-oligosaccharides.