Chloroplast-Derived Enzyme Cocktails Hydrolyse Lignocellulosic Biomass and Release Fermentable Sugars

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Departmental Papers (Dental)
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Biofuel
Renewable Energy
Cellulosic Ethanol
Cell Wall Degrading Enzymes
Fermentable Sugars
Lignocellulosic biomass
Dentistry
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Verma, Dheeraj
Kanagaraj, Anderson
Jin, Shuangxia
Singh, Nameirakpam D.
Kolattukudy, Pappachan E.
Daniell, Henry
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Abstract

It is widely recognized that biofuel production from lignocellulosic materials is limited by inadequate technology to efficiently and economically release fermentable sugars from the complex multi-polymeric raw materials. Therefore, endoglucanases, exoglucanase, pectate lyases, cutinase, swollenin, xylanase, acetyl xylan esterase, beta glucosidase and lipase genes from bacteria or fungi were expressed in E. coli or tobacco chloroplasts. A PCR based method was used to clone genes without introns from Trichoderma reesei genomic DNA. Homoplasmic transplastomic lines showed normal phenotype and were fertile. 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. Chloroplast-derived enzymes had higher temperature stability and wider pH optima than enzymes expressed in E. coli. Plant crude-extracts showed higher enzyme activity than E. coli with increasing protein concentration, demonstrating their direct utility without purification. Addition of E. coliextracts to the chloroplast-derived enzymes significantly decreased their activity. Chloroplast-derived crude-extract enzyme cocktails yielded more (up to 3,625%) glucose from filter paper, pine wood or citrus peel than commercial cocktails. Furthermore, pectate lyase transplastomic plants showed enhanced resistance to Erwina soft rot. 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.

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2010-04-01
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Plant Biotechnology Journal
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At the time of publication, author Henry Daniell was affiliated with University of Central Florida. Currently, (s)he is a faculty member at the School of Dental Medicine at the University of Pennsylvania.
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