Direct glucose production from lignocellulose using Clostridium thermocellum cultures supplemented with a thermostable β-glucosidase

Biotechnology for Biofuels

Panida Prawitwong³  Rattiya Waeonukul²  Chakrit Tachaapaikoon²  Patthra Pason²  Khanok Ratanakhanokchai¹  Lan Deng³  Junjarus Sermsathanaswadi¹  Krisna Septiningrum⁴  Yutaka Mori³  Akihiko Kosugi⁴ 

[1] School of Bioresources and Technology, King Mongkut’s University of Technology Thonburi (KMUTT), Bangkok, Thailand

[2] Pilot Plant Development and Training Institute (PDTI), King Mongkut’s University of Technology Thonburi (KMUTT), Bangkok, Thailand

[3] Biological Resources and Post-harvest Division, Japan International Research Center for Agricultural Sciences (JIRCAS), 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan

[4] University of Tsukuba Graduate School of Life and Environmental Sciences, 1-1-1 Ten-noudai, Tsukuba, Ibaraki 305-8572, Japan

关键词: Cellulosomes;    Biological saccharification;    Glucose production;    β-glucosidases;    Clostridium thermocellum;   

Others  :  794263
DOI  :  10.1186/1754-6834-6-184

 received in 2013-10-02, accepted in 2013-12-05,  发布年份 2013

【 摘 要 】

Background

Cellulases continue to be one of the major costs associated with the lignocellulose hydrolysis process. Clostridium thermocellum is an anaerobic, thermophilic, cellulolytic bacterium that produces cellulosomes capable of efficiently degrading plant cell walls. The end-product cellobiose, however, inhibits degradation. To maximize the cellulolytic ability of C. thermocellum, it is important to eliminate this end-product inhibition.

Results

This work describes a system for biological saccharification that leads to glucose production following hydrolysis of lignocellulosic biomass. C. thermocellum cultures supplemented with thermostable beta-glucosidases make up this system. This approach does not require any supplementation with cellulases and hemicellulases. When C. thermocellum strain S14 was cultured with a Thermoanaerobacter brockii beta-glucosidase (CglT with activity 30 U/g cellulose) in medium containing 100 g/L cellulose (617 mM initial glucose equivalents), we observed not only high degradation of cellulose, but also accumulation of 426 mM glucose in the culture broth. In contrast, cultures without CglT, or with less thermostable beta-glucosidases, did not efficiently hydrolyze cellulose and accumulated high levels of glucose. Glucose production required a cellulose load of over 10 g/L. When alkali-pretreated rice straw containing 100 g/L glucan was used as the lignocellulosic biomass, approximately 72% of the glucan was saccharified, and glucose accumulated to 446 mM in the culture broth. The hydrolysate slurry containing glucose was directly fermented to 694 mM ethanol by addition of Saccharomyces cerevisiae, giving an 85% theoretical yield without any inhibition.

Conclusions

Our process is the first instance of biological saccharification with exclusive production and accumulation of glucose from lignocellulosic biomass. The key to its success was the use of C. thermocellum supplemented with a thermostable beta-glucosidase and cultured under a high cellulose load. We named this approach biological simultaneous enzyme production and saccharification (BSES). BSES may resolve a significant barrier to economical production by providing a platform for production of fermentable sugars with reduced enzyme amounts.

【 授权许可】

   
2013 Prawitwong et al.; licensee BioMed Central Ltd.

【 图 表 】

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