From lignocellulose to whole bacteria catalyst
How to realize the high-value utilization of low-value raw materials of lignocellulosic biomass has been a research hotspot at home and abroad.
The metabolomics team of the Qingdao Institute of Bioenergy and Process of the Chinese Academy of Sciences aims to break the technological monopoly of foreign countries and break through the bottleneck of lignocellulose saccharification technology. It has long been committed to genetic modification and metabolic engineering research of cellulose-degrading bacteria such as Clostridium thermocellum Using a series of genetic manipulation tools developed earlier by the team, through the targeted transformation of Clostridium thermocellum and its cellulose-degrading enzyme system-fibrosomes, a new type of engineering strain was constructed, which can be used as a whole bacteria catalyst to achieve lignocellulose. The efficient conversion of substrates to fermentable sugars has strongly promoted the industrialization of lignocellulose biotransformation.
Lignocellulosic biomass has attracted much attention due to its reserves and reproducibility, but the irrational disposal of agricultural and forestry wastes will greatly increase environmental pressures and cause serious environmental pollution problems including water pollution and incineration smog. Therefore, the efficient use of non-grain lignocellulose is a global problem to be solved urgently, and has important strategic significance for achieving sustainable economic development. However, the industrialization, large-scale and commercial application of lignocellulosic biomass has not really started, and the bottleneck step of converting lignocellulose into fermentable sugar efficiently and at low cost is not the main reason.
Fibrosomes are one of the most efficient cellulose-degrading molecular machines known in nature. As a typical fibrosome-producing strain, Clostridium thermocellum has the characteristics of natural and efficient degradation of cellulose substrates, so it is considered to be the most effective Prospective strains that can achieve efficient biocatalytic transformation of lignocellulose based on strategies that integrate bioprocessing technologies. However, the existing wild strains and their fibrosomes have disadvantages such as the substrate hydrolytic activity being inhibited by the feedback of enzyme catalyzed products, and cannot meet the requirements of industrialization.
According to the current status of this research, the metabolomics team has targeted the transformation of Clostridium thermocellum and its fibrosomes. By establishing a scar-free genome editing system, β-glucosidase CaBglA derived from extreme thermophiles Fusion expression with the key fibrosomal enzyme Cel48S and assembly on extracellular fibrosomes. Using this recombinant strain as a whole bacteria catalyst for saccharification, it was found that when 100 g / L microcrystalline cellulose was used as a substrate, the reducing sugar yield reached 489 mM (about 88 g / L in terms of glucose molecular weight conversion). The ability of the bacteria to efficiently degrade cellulose and produce fermentable sugars has initially proved the feasibility of the whole-cell catalytic saccharification strategy of lignocellulose in industrial applications. This research expands a new horizon of saccharification of lignocellulose and has strongly promoted the substitution of cellulose sugar as a carbon source for starch sugar in the field of industrial fermentation.
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