Microbial enzyme systems for biomass conversion: emerging paradigms

Himmel, Michael E.; Xu, Qi; Luo, Yuhua; Ding, Shi You; Lamed, Raphael; Bayer, Edward A.

doi:10.4155/bfs.09.25

Cited by 172 publications

(125 citation statements)

References 126 publications

(116 reference statements)

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“…Previous studies have demonstrated the high efficiency of cellulosomes for the degradation of cellulose and hemicellulose, due to the spatial proximity of synergistically acting enzymes and to the locally increased concentrations in enzymes and substrate (31). However, cellulosomal systems discovered to date all appear to be lacking some of the key oxidative enzymes produced by the majority of aerobic lignocellulolytic microbes involved in the reduction of cellulose crystallinity and in lignin breakdown.…”

Section: Significancementioning

confidence: 99%

Toward combined delignification and saccharification of wheat straw by a laccase-containing designer cellulosome

Davidi

Moraïs

Artzi

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Efficient breakdown of lignocellulose polymers into simple molecules is a key technological bottleneck limiting the production of plant-derived biofuels and chemicals. In nature, plant biomass degradation is achieved by the action of a wide range of microbial enzymes. In aerobic microorganisms, these enzymes are secreted as discrete elements in contrast to certain anaerobic bacteria, where they are assembled into large multienzyme complexes termed cellulosomes. These complexes allow for very efficient hydrolysis of cellulose and hemicellulose due to the spatial proximity of synergistically acting enzymes and to the limited diffusion of the enzymes and their products. Recently, designer cellulosomes have been developed to incorporate foreign enzymatic activities in cellulosomes so as to enhance lignocellulose hydrolysis further. In this study, we complemented a cellulosome active on cellulose and hemicellulose by addition of an enzyme active on lignin. To do so, we designed a dockerin-fused variant of a recently characterized laccase from the aerobic bacterium Thermobifida fusca. The resultant chimera exhibited activity levels similar to the wild-type enzyme and properly integrated into the designer cellulosome. The resulting complex yielded a twofold increase in the amount of reducing sugars released from wheat straw compared with the same system lacking the laccase. The unorthodox use of aerobic enzymes in designer cellulosome machinery effects simultaneous degradation of the three major components of the plant cell wall (cellulose, hemicellulose, and lignin), paving the way for more efficient lignocellulose conversion into soluble sugars en route to alternative fuels production.

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Section: Significancementioning

confidence: 99%

Toward combined delignification and saccharification of wheat straw by a laccase-containing designer cellulosome

Davidi

Moraïs

Artzi

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Scaffoldin subunit is an anchoring protein which has a dual function of incorporating various enzymatic subunits through the tight interactions between the cohesin and dockerin moieties and binding to the substrate with the help of carbohydrate-binding module (CBM) Himmel et al 2010). In some microorganisms, multiple scaffoldins have been reported where a primary scaffoldin is anchored by a secondary scaffoldin subunit for amplifying the catalytic moieties onto the surface (Doi 2008).…”

Section: Scaffoldinmentioning

confidence: 99%

Bioprospecting thermostable cellulosomes for efficient biofuel production from lignocellulosic biomass

Arora

Behera

Sharma

et al. 2015

Bioresour. Bioprocess.

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The adverse climatic conditions due to continuous use of fossil-derived fuels are the driving factors for the development of renewable sources of energy. Current biofuel research focuses mainly on lignocellulosic biomass (LCB) such as agricultural, industrial and municipal solid wastes due to their abundance and renewability. Although many mesophilic cellulolytic microorganisms have been reported, efficient and economical bioconversion to simple sugars is still a challenge. Thermostable cellulolytic enzymes play an indispensible role in degradation of the complex polymeric structure of LCB into fermentable sugar stream due to their higher flexibility with respect to process configurations and better specific activity than the mesophilic enzymes. In some anaerobic thermophilic/thermotolerant microorganisms, few cellulases are organized as unique multifunctional enzyme complex, called the cellulosome. The use of cellulosomal multienzyme complexes for saccharification seems to be a promising and cost-effective alternative for complete breakdown of cellulosic biomass. This paper aims to explore and review the important findings in cellulosomics and forward the path for new cutting-edge opportunities in the success of biorefineries. Herein, we summarize the protein structure, regulatory mechanisms and their expression in the host cells. Furthermore, we discuss the recent advances in specific strategies used to design new multifunctional cellulosomal enzymes, which can function as lignocellulosic biocatalysts and evaluate the roadblocks in the yield and stability of such designer thermozymes with overall progress in lignocellulose-based biorefinery.

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“…There are also reviews on cellulase engineering and other in vitro strategies towards improving the functionality of cellulases (Bayer et al 2008;Himmel et al 2010;Schoffelen and van Hest 2012). However, the fraternity still faces challenges in terms of robustness, hydrolysis efficiency, and cost of these crucial enzymes.…”

Section: Introductionmentioning

confidence: 99%

Lignocellulases: a review of emerging and developing enzymes, systems, and practices

Obeng

Adam

Budiman

et al. 2017

Bioresour. Bioprocess.

132

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The highly acclaimed prospect of renewable lignocellulosic biocommodities as obvious replacement of their fossilbased counterparts is burgeoning within the last few years. However, the use of the abundant lignocellulosic biomass provided by nature to produce value-added products, especially bioethanol, still faces significant challenges. One of the crucial challenging factors is in association with the expression levels, stability, and cost-effectiveness of the cellulose-degrading enzymes (cellulases). Interestingly, several recommendable endeavors in the bid to curb these challenges are in pursuance. However, the existing body of literature has not well provided the updated roadmap of the advancement and key players spearheading the current success. Moreover, the description of enzyme systems and emerging paradigms with high prospects, for example, the cell-surface display system has been ill-captured in the literature. This review focuses on the lignocellulosic biocommodity pathway, with emphasis on cellulase and hemicellulase systems. The paradigm shift towards cell-surface display system and its emerging recommendable developments have also been discussed. The attempts in supplementing cellulase with other enzymes, accessory proteins, and chemical additives have also been discussed. Moreover, some of the prominent and influential discoveries in the cellulase fraternity have been discussed.

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Microbial enzyme systems for biomass conversion: emerging paradigms

Cited by 172 publications

References 126 publications

Toward combined delignification and saccharification of wheat straw by a laccase-containing designer cellulosome

Toward combined delignification and saccharification of wheat straw by a laccase-containing designer cellulosome

Bioprospecting thermostable cellulosomes for efficient biofuel production from lignocellulosic biomass

Lignocellulases: a review of emerging and developing enzymes, systems, and practices

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