Photosynthetic Biofuels Issues and Prospects

Transcription

1 Photosynthetic Biofuels Issues and Prospects Tasios Melis University of California - Berkeley Monday, 30-Mar-2009 Solar Biofuels from Microorganisms Lorentz Center, Leiden 1

2 Photosynthetic Biofuels Entails a process whereby one and the same organism serves as both the photo-catalyst and the producer of ready-made fuel. 2

3 Topics of Lecture Photosynthesis / Productivities Hydrogen Hydrocarbons Improving the Performance of P 3

4 Feedstock and products H 2 O Photons CO 2 Photosynthesis H 2 O 2, Biomass HC Process offers a renewable energy supply and mitigation of climate change. 4

5 Sunlight Average US Solar insolation = 5 kwh m -2 d -1 US household electricity consumption = 15 kwh d -1 1 kg hydrogen = 1 gallon gasoline = 40 kwh 5

6 Solar Conversion Efficiencies Incident Sunlight Energy (100%) Absorbed Sunlight, (VIS) (45%) Stored PS chemical energy (30%) 20 0 Hydrogen (12%) Biomass (8-10%) 6

7 Criteria for Selecting Organisms Solar-to-biofuel conversion efficiency must be as high as possible* * high performance in photosynthesis * minimal photosynthesis-to-biofuel steps 7

8 The green microalga Chlamydomonas reinhardtii Differential Interference Contrast Chlorophyll Fluorescence 8

9 Photosynthetic Productivities (Commercial Biomass Production) Chlorella (green microalga): ton dw acre -1 y -1 Spirulina (cyanobacterium): 5-10 ton dw acre -1 y -1 Switchgrass : 2-4 ton dw acre -1 y -1 9

10 Criteria for Selecting Biofuels High relative energy content Biofuel separation from the biomass. 10

11 Photosynthetic water oxidation and H 2 -production Potential Energy, mv hv Q PQ Cyt b e - e - Cyt f PC A e - P 700 PS I e - FD e - FNR NADP + hv HydAH 2 ase NADPH 2H 2 4H + +1,000 mv P 680 PS II 4e - + 4H + + O 2 2H 2 O ~3,000,000 electron transport chains per cell, each capable of transporting electrons per second

12 Anaerobic photosynthesis: O 2 is consumed by mitochondria Photo 2H 2 O > [Fe]-H 2 ase O 2 4H + 4H + 2H 2 O 2 < NADH<---[starch] 2H 2 O phosphorylation Oxidative phosphorylation chloroplast mitochondria 12

13 Effect of S-deprivation on P and R Activity, mmol O 2 [mol Chl] -1 s P R Time in S-deprivation, h 13

14 H 2 gas collected, ml H 2 gas accumulates when P/R < ml h -1 Light Dark Time in S-deprivation, h 14

15 H 2 bubbles 15

16 H 2 gas collected, ml Cycling of the Stages Cycle A Cycle B Cycle C +S +S Time, h 16

17 Chlamydomonas reinhardtii SO 4 2- SO 4 2- SO 4 2- SO 4 2- sulp antisense transformants SO 4 2- cytoplasm chloroplast APS SO 3 2- S 2- Cysteine Cp Proteins Limiting rates of Cp protein biosynthesis 17

18 The C. reinhardtii Chloroplast Sulfate Permease is an ABC-type Transporter cytosol Sbp 2- SO 4 Sbp SulP Sulp2 envelope stroma Sabc ATP Sabc ATP 18

19 H2 gas production, ml >150 µm sulfate in the medium Sealing of cultures anti-sulp Time, h anti-sulp-12 wild type 19

20 Microalgal H 2 -production facility in the laboratory 20

21 Hydrogen production in a backyard 21 Chlamydomonas reinhardtii mass culture

22 Tubular Racetrack Photoreactor Design Direction of flow Control Box green algae green algae green algae green algae Tubular racetrack low-cost photoreactor facility for microalgae, designed to support cell growth, H 2 or hydrocarbon production. Depending on the optical properties of the cells, tube diameter would be 6-12 inches wide. 22

23 Photosynthesis and metabolism Photosynthesis Calvin RuBP + GA 3-P CO 2 Cycle 1 SUGARS [to Cellulose --> --> to Ethanol] 3-PGA Pyruvate 3 Acetyl-coA 2 Deoxy-xylulose-5-P Isopentenyl~PP Fatty acids Isoprenoids 23

24 Photosynthesis and metabolism Photosynthesis Calvin RuBP + GA 3-P CO 2 Cycle 1 SUGARS [to Cellulose --> --> to Ethanol] 3-PGA Pyruvate 3 Acetyl-coA 2 Deoxy-xylulose-5-P Isopentenyl~PP Fatty acids Isoprenoids (C 10 H 16, C 20 H 30, C 30 H 48, C 40 H n ) 24

25 Liquid cultures of microalgae Bio-oil coating of the wall Chlamydomonas culture Botryococcus culture 25

26 Naturally-accumulating hydrocarbons Schematic by Metzger and Largeau

27 Hydrogen vs Hydrocarbons H 2 High solar-to-product conversion efficiency; Easy product separation from biomass; Very clean technologies; Leaky; Storage; Transportation; Infrastructure Hydrocarbons Stored hydrogen; Transportation; Utilization; Infrastructure Lower solar-to-product conversion efficiency; Not always easy to separate from biomass. 27

28 Hydrogen production in a backyard 28 Chlamydomonas reinhardtii mass culture

29 The light saturation curve of photosynthesis Oxygen evolution, mmol O 2 (mol Chl) -1 s wild type Light intensity, µmol photons m -2 s -1 29

30 Example: Fully Pigmented P The green algae Chlamydomonas reinhardtii Sunlight Heat dissipation Fully pigmented cells over-absorb and wastefully dissipate bright sunlight 30

31 Design Solar of Conversion Organism Efficiency Modification Minimize the chlorophyll antenna size to improve solar conversion efficiency in mass culture. 31

32 Example: Truncated Chl Antenna Size P P P P Sunlight Heat dissipation Truncated Chl antenna cells permit greater transmittance of light and overall better solar utilization by the culture 32

33 Regulation of the Chl antenna size Large Chl Antenna Size (600 Chl a and b) Genetic determinants Truncated Chl Antenna Size (130 Chl a) Interference with the genetic mechanism for the regulation of the Chl antenna size, to derive a permanently truncated Chl antenna size, is the goal of this R&D. 33

34 DNA Insertional Mutagenesis and Screening for Chl Antenna Size Mutants Dot-Spot Colonies of Chlamydomonas reinhardtii 34

35 tla1 low control high Chlorophyll a fluorescence imaging analysis 35

36 Screening for Tla mutants Measurements required: Functional PS Chl antenna size PSII and PSI RC per Cp or cell Quantum yield of photosynthesis P max and productivity 36

37 tla1 mutant complementation WT tla1- comp3 tla1- comp2 tla1- comp1 tla1 Complementation of the pale-green tla1 mutant with the wild type Tla1 gene resulted in tla1- comp1, tla1-comp2, and tla1-comp3 strains with restored dense green pigmentation properties. 37

38 Wild type Tla1 gene PROMOTER TAA 3 UTR Coding Intron Coding 5 UTR tla1 mutant gene pjd67 ARG7 ATG TAA 38

39 Alignment of Tla1-like proteins 39

40 Lower levels of the Tla1 protein are found in the tla1 mutant W T ST T - tla1 W - wild type ST - Standards 24.9 kd W T 23.2 kd 40

41 The light-harvesting chlorophyll antenna size of the tla1 mutant Wild Type Chl Antenna Size ~ 600 Chl a + b molecules tla1 mutant Chl antenna size 300 Chl a + b molecules 41

42 The light-saturation curve of photosynthesis tla1 WT

43 Productivity in Mass Culture Cultures in the Greenhouse tla1 Parameter WT tla1 Cell/mL (x10 6 ) WT [Chl] (um) The tla1 strain shows greater productivity than the wild type cells under bright sunlight conditions. (Note relative amounts of gas bubbles produced by the two samples.) 43

44 Photosynthetic productivity of C. reinhardtii wild type and tla1 mutant O 2 production, ml h tla1 WT Chl in the culture, µm 44

45 Summary and Conclusions Photosynthesis can be directed toward H 2 or hydrocarbon production in microalgae A smaller, or truncated, Chl antenna size of the microalgae in mass culture: Facilitates better sunlight penetration, Enhances solar conversion efficiency and productivity. 45

46 Thank you for your Attention 46