Characterization Of β-glucosidase Bgl 2, Bgl 15 And Bgl 17 From Metagenome Of Termite Gut

With the increasing depletion of fossil fuels, the energy issue has become one of the major problems of facing society. Lignocellulose is an important storage form of solar energy and is the most abundant renewable resource on the earth. The lignocellulose is used to produce ethanol and other biofuel, which can recycle the waste materials, and partially alleviate the growing demand for energy. Therefore, the research and exploitation of novel lignocellulases with higher activity, higher stability and higher temperature resistance are important for industrial applications. Moreover, lignocellulase is also widely used in food processing, textile, animal feed, papermaking and so on. In the degrading process of lignocellulose, β-glucosidase can directly hydrolysis the short chain oligosaccharides to glucose, which is a rate-limiting step. Therefore, the research and development of novelβ-glucosidase are of great significance.Termites mainly feed on lignocellulose and have high efficiency in degrading lignocellulose. Studies have shown that there are a lot of symbiosis microbes in termite gut.Meanwhile, the microbes play a crucial role in the process of cellulose degradation. And the gut microbiota are one of the important resources used to exploit the enzyme of lignocellulose degradation. With the advance of molecular biotechnology, metagenomic technology has become an effective tool for lignocellulase research.In this paper, three novel β-glucosidase encoding gene including bgl 2, bgl 15 and bgl17 were identified from the functional screening of a metagenomic library constructed from the gut of Globitermes sulphureus, which were heterologous expressed and characterized. Bgl 17 was belong to glycoside hydrolase family 1(GHF1), whose optimal temperature and pH with p-nitrophenyl-β-D-glucoside(pNPG) were 70 ℃ and 5.0,respectively. The specific activity of Bgl 17 was 115.69 U/mg on the optimal condition. The Km and Vmax of purified Bgl 17 were 0.81 mmol/L and 227.27 μmol/(ml?min), respectively.Bgl 2 and Bgl 15 were belong to glycoside hydrolase family 3(GHF3), and the optimal temperature with pNPG were 40 ℃ and 45 ℃, respectively. The optimal pH of Bgl 2 was4.5, and Bgl 15 can tolerate a widely pH range, which can keep highest activity from pH 5.0– 9.0. The specific activity of Bgl 2 and Bgl 15 were 21.7 U/mg and 2.33 U/mg on the optimal condition, respectively.These results suggest that the three β-glucosidase which were screened from the metagenomic library of termite gut have different characteristics. They can adapt to different conditions of temperature and pH, which have the potential industrial applications. Inaddition, the optimal temperature of Bgl 17 was much higher than the termites’ living environment, which could provide the reference for the mechanism of cellulose degradation of termites...