New engineering strains as whole bacteria catalysts promote industrialization of lignocellulose biotransformation

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 (J Microbiol Methods, 2012, 89: 201-8 .; PloS One 2013, 8: e69032; Appl Microbiol Biotechnol, 2014, 98: 313-23; Biotechnol Biofuels, 2015, 8:36.), Through the targeted transformation of Clostridium thermocellum and its cellulose-degrading enzyme system, fiber bodies, a new engineering strain was constructed, which can be used as a whole-bacterial catalyst to achieve lignocellulosic substrates to fermentable sugar The high-efficiency conversion has strongly promoted the industrialization of lignocellulose biotransformation.

Related results have been published online on May 12 in Biotechnology for Biofuels [Zhang J, et al, 2017, 10 (1): 124]. Among them, Zhang Jie, PhD student, is the first author of the paper, researcher Cui Qiu and associate researcher Yajun Liu is the corresponding author of the paper.

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. The main reason is that it has not yet broken through the bottleneck step of efficient and low-cost conversion of lignocellulose into fermentable sugars.

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. It is considered to be the most promising strain that can achieve efficient biocatalytic transformation of lignocellulose based on the strategy of integrating bioprocessing technology. 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.

In response to this research situation, the metabolomics team has targeted the transformation of Clostridium thermocellum and its fibrosomes, and 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).

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.