Tobacco Plant-derived Enzyme Cocktail for Efficient and Low-Cost Hydrolysis of Biomass for Cellulosic Ethanol Production
One of the barriers to cost-effective production of cellulosic ethanol is inadequate technology to efficiently and economically release fermentable sugars from cellulosic biomass. Companies such as Novozymes have worked for years to reduce the cost and improve the efficiency of their enzymes for this type of application. (Earlier post.)
Now, researchers at the University of Central Florida have developed a tobacco plant-derived cocktail of enzymes for the efficient hydrolysis of a range of lignocellulosic biomass. The new crude-extract enzyme cocktails yielded more (up to 3,625%) glucose from filter paper, pine wood or citrus peel than commercial cocktails. A paper on the work was published online 13 January in the Plant Biotechnology Journal.
The team led by University of Central Florida professor Henry Daniell expressed genes for endoglucanases, exoglucanase, pectate lyases, cutinase, swollenin, xylanase, acetyl xylan esterase, beta glucosidase and lipase genes from bacteria or fungi in Escherichia coli bacteria and the chloroplasts of tobacco plants.
Tobacco was chosen as an ideal system for enzyme production for several reasons: it is not a food crop, and an estimated 40 metric tons of biomass are produced annually in each acre of tobacco plants. Enzyme production also would provide an alternate use for this crop and potentially decrease its use for smoking.
Producing these enzymes in tobacco instead of manufacturing synthetic versions could reduce the cost of production by a thousand times, which means the cost of making ethanol should be significantly reduced, Daniell said.
Based on observed expression levels, up to 49, 64 and 10, 751 million units of pectate lyases or endoglucanase can be produced annually, per acre of tobacco. Plant production cost of endoglucanase is 3,100-fold, and pectate lyase is 1,057 or 1,480-fold lower than the same recombinant enzymes sold commercially, produced via fermentation.—Verma et al.
The researchers found that the choloroplast-derived enzymes from the tobacco plants had higher temperature stability and wider pH optima that the enzymes expressed in E. coli. The plant crude-extracts showed higher enzyme activity than E. coli with increasing protein concentration, demonstrating their direct utility without purification.
This is the first report of using plant-derived enzyme cocktails for production of fermentable sugars from lignocellulosic biomass. Limitations of higher cost and lower production capacity of fermentation systems are addressed by chloroplast-derived enzyme cocktails.—Verma et al.
Daniell’s team included Dheeraj Verma, Anderson Kanagaraj, Shuangxia Jin, Nameirakpam Singh and Pappachan E. Kolattukudy in the Burnett School of Biomedical Sciences at UCF’s College of Medicine. Genes for pectinase enzyme were cloned in Kolattukudy’s laboratory. The US Department of Agriculture funded the research.
Dheeraj Verma, Anderson Kanagaraj, Shuangxia Jin, Nameirakpam D. Singh, Pappachan E. Kolattukudy, Henry Daniell (2010) Chloroplast-derived enzyme cocktails hydrolyse lignocellulosic biomass and release fermentable sugars. Plant Biotechnology Journal doi: 10.1111/j.1467-7652.2009.00486.x