Polyhydroxyalkanoates: Microbial Biopolymers

1. Polyhydroxyalkanoates: Microbial Biopolymers Peter Jantz Chemistry 496 May 7th, 2004

2. Overview • Traditional Polymers • What are Biopolymers? • How Biopolymers are Synthesized • Environmental Benefits • The Future of Biopolymers

3. Traditional Polymers: Structure Polystyrene: Coffee cups, Fast-food Polyethylene: HDPE: Milk containers LDPE: Plastic bags, Packaging Polyvinyl chloride: Piping, Meat wrap Polyethylene terephthalate: Soda bottles

4. Expenses of Traditional Polymers • Production of 1 pound of polystyrene requires 2.26 pounds of oil. • 1 lb provides the carbon monomers and the remaining 1.26 lbs of oil are burned to produce the electrical power to run the reaction. • Organic solvent: 1,2-dichloroethane (~$30 per liter) • Reaction Initiator: boron trifluoride with water (~$20 per gram)

5. Environmental effects • Oil use: 100 billion pounds of plastics are produced in North America annually • Only 3% of these plastics are recycled • Barely 25% of all soda bottles are recycled

6. What are Biopolymers? • Energy storage for bacteria • Physical properties of polyethylene, polystyrene, and synthetic polyesters • Polyhydroxyalkanoates Polyhydroxybutyrate Polyhydroxyvalerate

7. Synthetic Conditions • Anaerobic Environment • Abundant carbon source • 3-hydroxyacyl-CoA polymerization

8. PHA Synthesis from fatty acids

9. PHA Synthesis from a carbon source

10. 3-hydroxyacyl CoA polymerization

11. Processing • A carbon source (corn) is ground into a mash and ‘fed’ to PHA-forming bacteria • Glucose is extracted as the microbes ferment the mash and store the energy as PHA’s • The cells are washed and lysed • The PHA’s are separated by centrifuge and washed again 30% PHA by dry weight

12. Biodegradability

13. 3x higher than petroleum-based plastics High start-up costs Labor intensive processing High energy demands Monetary Costs

14. Good Ocean pollution would decrease Landfill space would decrease (anaerob.) Recycling costs could be saved Bad Air pollution would increase significantly 2.39 pounds of fossil fuel are burned for each pound of PHA produced Environmental effects =o) =o(

15. Is there a future for Biopolymers? With greater financial and environmental costs, how will renewable biodegradable polymers take a hold in industry and with consumers?

16. Mustard!!

17. Genetic transfer to plants • Mustard and alfalfa • Restriction Endonuclease gene insertion • Use carbon-dioxide as carbon source • 14% PHA by dry weight • Cheaper processing

18. References: [1] T. Gerngross. “Plastic from plants called costly” New Orleans ACS meeting. August 25, 1999 [2] C. Nawrath et al. Targeting of the polyhydroxybutyrate biosynthetic pathway to the plastids of Arabidopsis thaliana results in high levels of polymer accumulation. Proc. Natl. Acad. Sci. U.S.A., 12760, 1994. [3] Yong Jia et al. Mechanistic Studies on Class I Polyhydroxybutyrate (PHB) Synthase from Ralstonia eutropha: Class I and III Synthases Share a Similar Catalytic Mechanism. Biochemistry, 1011 -1019, 2001. [4] Shiming Zhang et al. Mechanism of the Polymerization Reaction Initiated and Catalyzed by the Polyhydroxybutyrate Synthase of Ralstonia eutropha. Biomacromolecules, 504 -509, 2003. [5] Si Jae Park et al. Production of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) by Metabolically Engineered Escherichiacoli Strains. Biomacromolecules, 248 -254, 2001. [6] Lin Su et al. Enzymatic Polymerization of (R )-3- Hydroxyalkanoates by Bacterial Polymerase. Macromolecules, 229 -231, 2000.

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