Abstract
Plant biomass-based biofuels have gradually substituted for conventional energy sources thanks to their obvious advantages, such as renewability, huge quantity, wide availability, economic feasibility, and sustainability. However, to make use of the large amount of carbon sources stored in the plant cell wall, robust cellulolytic microorganisms are highly demanded to efficiently disintegrate the recalcitrant intertwined cellulose fibers to release fermentable sugars for microbial conversion. The Gram-positive, thermophilic, cellulolytic bacterium Clostridium thermocellum possesses a cellulolytic multienzyme complex termed the cellulosome, which has been widely considered to be nature’s finest cellulolytic machinery, fascinating scientists as an auspicious source of saccharolytic enzymes for biomass-based biofuel production. Owing to the supra-modular characteristics of the C. thermocellum cellulosome architecture, the cellulosomal components, including cohesin, dockerin, scaffoldin protein, and the plentiful cellulolytic and hemicellulolytic enzymes have been widely used for constructing artificial cellulosomes for basic studies and industrial applications. In addition, as the well-known microbial workhorses are naïve to biomass deconstruction, several research groups have sought to transform them from non-cellulolytic microbes into consolidated bioprocessing-enabling microbes. This review aims to update and discuss the current progress in these mentioned issues, point out their limitations, and suggest some future directions.
Highlights
During evolution, cellulolytic microbes developed an extracellular multienzyme complex called the cellulosomes to boost the cellulose degradation rate at maximum levels [1]
There are several conjugation techniques to design artificial cellulosomes [9], the present review mainly focuses on the CohI–DocI interaction-based artificial cellulosome construction
C. thermocellum cellulosome is among the fastest and most efficient biocatalysts known for decomposing lignocellulosic biomass, the low yield of its fermentation products limits the application of this bacterium in biofuel production systems
Summary
Cellulolytic microbes developed an extracellular multienzyme complex called the cellulosomes to boost the cellulose degradation rate at maximum levels [1]. To convert non-cellulolytic biofuels-producing microbes into consolidated bioprocessing (CBP)-enabling microbes, which can conduct enzyme production, substrate saccharification, and fermentation of the released sugars into biofuels in a single step, various studies have been carried out to express heterologous cellulolytic enzymes in heterologous host cells to make them genetically engineered cellulolytic microbes [11]. These engineered microbes use a cell-surface display or secretion system to display their novel hydrolytic capability.
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