This document discusses modifying plant cell walls to increase biofuel production. The plant cell wall contains cellulose, hemicellulose and lignin that can be broken down into fermentable sugars for biofuel but is resistant to degradation. The document proposes several strategies to modify the plant cell wall including decreasing lignin content, increasing cellulose density, incorporating soluble monomers, and expressing enzyme cocktails like cellulases in chloroplasts to more efficiently break down cell walls into fermentable sugars for biofuel production.

1. Plant Cell Wall Modification
for the Production of Biofuel
By Ben Merritt

2. Why Modify the Cell Wall?
• We are running out of unsustainable fuel
sources
• Plant cell wall contains “locked up” source of
carbon

3. Composition of Plant Cell Wall
• 3 layers
• Middle Lamella (outermost from cytoplasm;
connects cells); made of pectin
• Primary; made of pectin, cellulose,
hemicellulose, proteins
• Secondary; made of cellulose, hemicellulose,
lignin (only in mature cells)

5. Cellulose (Cellubiose)

6. Cellulose (Crystalline)

7. Cellulose Arrangement

9. Hemicellulose vs. Cellulose

10. Hemicellulose (Xylan), continued

11. Lignin

12. Biomass
Production

13. Yeast Fermentation

14. Perfect Biomass Plant?
• High Cellulose content
• Low lignin content
• Low ash content (unusable inorganics)

16. First/Second Generation Biofuel
• 1st
= using edible sugars (sucrose) from food
crops for fuel production
• 2nd
= using non-edible, structural
polysaccharides for fuel production

17. 2nd
Generation Biofuels
• 1.5 billion tons of unused plant material each
year
• Is estimated to be equivalent to total oil
imports (442 billion liters of EtOH)

18. Acid Growth – Natural Cell Wall
Modification
• Mediated by auxin (cell elongation)
• Physical teasing apart of cell wall
• Expansins, endoglucanases spread apart and
degrade parts

21. Enhance Efficiency of Reclaim for
Ethanol
• Increase cellulose/cell wall density
• Remove unwanteds (hemicellulose, lignin)
• Incorporate soluble monomers (makes
processing easier)
• Utilize glucanases (increases growth)
• Destroy lignin-cellulose bonds (decreases lignin)

22. Chloroplast-Derived Enzyme Cocktail
• One team inserted:
• Endo/exoglucanase or lipase from bacteria
• Pectate Lyases
• Cutinase
• Endoglucanases
• Swollenin
• Xylanase
• Acetyl Xylan Esterase
• Beta glucosidase

23. “Recalcitrance of Lignocellulosic
Material”
• Cellulose evolved to be tough
• Microbes are the main cell wall metabolizers
(bacteria, fungi)
• Endoglucanases also found in guts of termites,
cockraoches, grass carps, blue mussel

24. Acetobacter xylinum

25. References
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