Engineering Thermotolerant Biocatalysts for Biomass Conversion to Products

K. T. Shanmugam, L. O. Ingram and J. A. Maupin-Furlow

University of Florida

关键词: Bacillus;    Cellulose;    Bacillus Coagulans;    Plastics;    Ethanol;   

RP-ID  :  Final Report
RP-ID  :  FG36-04GO14019
RP-ID  :  979455

美国|英语

来源: UNT Digital Library

【 摘 要 】

Lignocellulosic biomass is a promising feedstock for producing renewable chemicals and transportation fuels as petroleum substitutes. Fermentation of the cellulose in biomass in an SSF process requires that the properties of the microbial biocatalyst match the fungal cellulase activity optima for cost-effective production of products. Fermentation of the pentose sugars derived from hemicellulose in biomass is an additional asset of an ideal biocatalyst. The microbial biocatalyst used by the industry, yeast, lacks the ability to ferment pentose sugars. The optimum temperature for growth and fermentation of yeast is about 35°C. The optimum temperature for commercially available cellulase enzymes for depolymerization of cellulose in biomass to glucose for fermentation is 50-55 °C. Because of the mismatch in the temperature optima for the enzyme and yeast, SSF of cellulose to ethanol (cellulosic ethanol) with yeast is conducted at a temperature that is close to the optimum for yeast. We have shown that by increasing the temperature of SSF to 50-55 °C using thermotolerant B. coagulans, the amount of cellulase required for SSF of cellulose to products can be reduced by 3-4 –fold compared to yeast-based SSF at 35°C with a significant cost savings due to lower enzyme loading. Thermotolerant Bacillus coagulans strains ferment hemicellulose-derived pentose sugars completely to L(+)-lactic acid, the primary product of fermentation. We have developed genetic tools to engineer B. coagulans for fermentation of all the sugars in biomass to ethanol. Using these tools, we have altered the fermentation properties of B. coagulans to produce ethanol as the primary product. The thermotolerant property of B. coagulans has been shown to also lower the cellulase requirement and associated cost in SSF of cellulose to lactic acid compared to lactic acid bacteria. Lactic acid is a potential petroleum substitute for bio-based renewable plastics production. This study has led to the development of B. coagulans as a thermotolerant microbial biocatalyst for production of ethanol as a transportation fuel and lactic acid as a starting material for bio-based plastics in a cost-effective manner from renewable biomass.