Course Project Engineering electricity production by living organisms

1. Course Project Engineering electricity production by living organisms http://biophotovoltaics.wordpress.com/

2. General principle: Bacteria transfer e- from food to anode via direct contact, nanowires or a mediator. H+ diffuse to cathode to join e- forming H2O

3. Geobacter species, Shewanella species In Geobacter sulfurreducens Om cytochromes transfer e- to anode.

4. In Geobacter sulfurreducens pili function as nanowires, but e- are not transferred via cytochromes. Pilin mutants have been isolated.

5. Nanowires have also been found in Shewanella oneidensisPseudomonas aeruginosa, Synechocystis PCC6803 in low CO2 (A) and Pelotomaculum thermopropionicum (C)

6. Plan A: Use plants to feed electrogenic bugs ->exude organics into rhizosphere

7. Many cyanobacteria reduce their surroundings in the light & make pili

8. Green algae (Chlorella vulgaris, Dunaliella tertiolecta) or cyanobacteria (Synechocystis sp. PCC6803, Synechococcus sp.WH5701were used for bio-photovoltaics

9. Energy Environ. Sci., 2011, 4, 4690. Use Z-scheme to move e- from H20 to FeCN, then to anode. H+ diffuse across membrane to cathode, where recombine with e- to form H2O

10. FeCN is best mediator = electrons come from PSI

13. conversion of CO2 to ethylene (C2H4) in Synechocystis 6803 transformed with efe gene. Use ethylene to make plastics, diesel, gasoline, jet fuel or ethanol

14. Changing Cyanobacteria to make a 5 carbon alcohol

15. Botryococcus braunii partitions C from PS into sugar/fatty acid/terpenoid at ratios of 50 : 10 : 40 cf85 : 10 : 5 in most plants

16. Engineering algae to make H2

17. Engineering algae to make H2

18. Making H2 in vitro using PSII

19. Making H2 in vitro using PSI

20. Making H2 in vitro using PSI & PSII

21. Using LHCII complexes to make H2 in vitro via platinum Energy Environ. Sci., 2011, 4, 181

22. PSI and PSII work together in the “Z-scheme” PSII gives excited e- to ETS ending at PSI Each e- drives cyt b6/f Use PMF to make ATP PSII replaces e- from H2O forming O2

23. Z-scheme energetics

24. Physical organization of Z-scheme • PS II consists of: P680 (a dimer of chl a) • ~ 30 other chl a& a few carotenoids • > 20 proteins • D1 & D2 bind P680 & all e- carriers

25. Physical organization of Z-scheme • PSII also has two groups of closely associated proteins • 1) OEC (oxygen evolving complex) • on lumen side, near rxn center • Ca2+, Cl- & 4 Mn2+ • 2) variable numbers of LHCII complexes

26. PSII Photochemistry 1) LHCII absorbs a photon 2) energy is transferred to P680

27. PSII Photochemistry 3) P680* reduces pheophytin ( chl a with 2 H+ instead of Mg2+) = primary electron acceptor

28. PSII Photochemistry 3) P680* reduces pheophytin ( chl a with 2 H+ instead of Mg2+) = primary electron acceptor charge separation traps the electron

29. PSII Photochemistry 4) pheophytin reduces PQA(plastoquinone bound to D2) moves electron away from P680+ & closer to stroma

30. PSII Photochemistry 5) PQA reduces PQB (forms PQB- )

31. PSII Photochemistry 6) P680+ acquires another electron , and steps 1-4 are repeated

32. PSII Photochemistry 7) PQA reduces PQB - -> forms PQB2-

33. PSII Photochemistry 8) PQB2- acquires 2 H+ from stroma forms PQH2 (and adds to ∆pH)

34. PSII Photochemistry 9) PQH2 diffuses within bilayer to cyt b6/f - is replaced within D1 by an oxidized PQ

35. Photolysis: Making Oxygen 1) P680+ oxidizes tyrZ ( an amino acid of protein D1)

36. Photolysis: Making Oxygen 2) tyrZ + oxidizes one of the Mn atoms in the OEC Mn cluster is an e- reservoir

37. Photolysis: Making Oxygen 2) tyrZ + oxidizes one of the Mn atoms in the OEC Mn cluster is an e- reservoir Once 4 Mn are oxidized replace e- by stealing them from 2 H2O

38. Shown experimentally that need 4 flashes/O2

39. Shown experimentally that need 4 flashes/O2 Mn cluster cycles S0 -> S4 Reset to S0 by taking 4 e- from 2 H2O

40. Electron transport from PSII to PSI • 1) PQH2 diffuses to cyt b6/f • 2) PQH2 reduces cyt b6 and Fe/S, releases H+ in lumen • since H+ came from stroma, transports 2 H+ across membrane (Q cycle)

41. Electron transport from PSII to PSI 3) Fe/S reduces plastocyanin via cyt f cyt b6 reduces PQ to form PQ-

42. Electron transport from PSII to PSI 4) repeat process, Fe/S reduces plastocyanin via cyt f cyt b6 reduces PQ- to form PQH2

43. Electron transport from PSII to PSI 4) PC (Cu+) diffuses to PSI, where it reduces an oxidized P700

44. Electron transport from PSI to Ferredoxin 1) LHCI absorbs a photon 2) P700* reduces A0 3) e- transport to ferredoxin via A1 & 3 Fe/S proteins

45. Electron transport from Ferredoxin to NADP+ 2 Ferredoxin reduce NADP reductase

46. Electron transport from Ferredoxin to NADP+ 2 Ferredoxin reduce NADP reductase NADP reductase reduces NADP+

47. Electron transport from Ferredoxin to NADP+ 2 Ferredoxin reduce NADP reductase NADP reductase reduces NADP+ this also contributes to ∆pH

48. Overall reaction for the Z-scheme 8 photons + 2 H2O + 10 H+stroma + 2 NADP+ = 12 H+lumen + 2 NADPH + O2

49. Chemiosmotic ATP synthesis PMF mainly due to ∆pH is used to make ATP -> very little membrane potential, due to transport of other ions thylakoid lumen pH is < 5 cf stroma pH is 8 pH is made by ETS, cyclic photophosphorylation,water splitting & NADPH synth

50. Chemiosmotic ATP synthesis Structure of ATP synthase CF1 head: exposed to stroma CF0 base: Integral membrane protein