Metabolic Diversity: Phototrophy, Autotrophy, Chemolithotrophy, and Nitrogen Fixation

1. Chapter 20 Metabolic Diversity: Phototrophy, Autotrophy, Chemolithotrophy, and Nitrogen Fixation Lectures by Buchan & LeCleir

2. I. The Phototrophic Way of Life • 20.1 Photosynthesis • 20.2 Chlorophylls and Bacteriochlorophylls • 20.3 Carotenoids and Phycobilins • 20.4 Anoxygenic Photosynthesis • 20.5 Oxygenic Photosynthesis

3. 20.1 Photosynthesis • Photosynthesis is the most important biological process on Earth • Phototrophs are organisms that carry out photosynthesis • Most phototrophs are also autotrophs • Photosynthesis requires light-sensitive pigments called chlorophyll • Photoautotrophy requires ATP production and CO2 reduction • Oxidation of H2O produces O2 (oxygenic photosynthesis) • Oxygen not produced (anoxygenic photosynsthesis)

4. Classification of Phototrophic Organisms Figure 20.1

5. Patterns of Photosynthesis Figure 20.2

6. Patterns of Photosynthesis Figure 20.2

7. 20.2 Chlorophylls and Bacteriochlorophylls • Organisms must produce some form of chlorophyll (or bacteriochlorophyll) to be photosynthetic • Chlorophyll is a porphyrin • Number of different types of chlorophyll exist • Different chlorophylls have different absorption spectra • Chlorophyll pigments are located within special membranes • In eukaryotes, called thylakoids • In prokaryotes, pigments are integrated into cytoplasmic membrane

8. Structure and Spectra of Chloro- and Bacteriochlorophyll Figure 20.3a

9. Structure and Spectra of Chloro- and Bacteriochlorophyll Absorption Spectrum Figure 20.3b

10. Structure of All Known Bacteriochlorophylls Figure 20.4

11. Structure of All Known Bacteriochlorophylls Figure 20.4

12. Structure of All Known Bacteriochlorophylls Figure 20.4

13. Photomicrograph of Algal Cell Showing Chloroplasts Figure 20.5a

14. Chloroplast Structure Figure 20.5b

15. 20.2 Chlorophylls and Bacteriochlorophylls • Reaction centers participate directly in the conversion of light energy to ATP • Antenna pigments funnel light energy to reaction centers • Chlorosomes function as massive antenna complexes • Found in green sulfur bacteria

16. Arrangement of Light-Harvesting Chlorophylls Figure 20.6

17. The Chlorosome of Green Sulfur and Nonsulfur Bacteria Electron Micrograph of Cell of Green Sulfur Bacterium Figure 20.7

18. The Chlorosome of Green Sulfur and Nonsulfur Bacteria Model of Chromosome Structure Figure 20.7

19. 20.3 Carotenoids and Phycobilins • Phototrophic organisms have accessory pigments in addition to chlorophyll, including carotenoids and phycobiliproteins • Carotenoids • Always found in phototrophic organisms • Typically yellow, red, brown, or green • Energy absorbed by carotenoids can be transferred to a reaction center • Prevent photo-oxidative damage to cells

20. Structure of -carotene, a Typical Carotenoid Figure 20.8

21. Structures of Some Common Carotenoids Figure 20.9

22. Structures of Some Common Carotenoids Figure 20.9

23. 20.3 Carotenoids and Phycobilins • Phycobiliproteins are main antenna pigments of cyanobacteria and red algae • Form into aggregates within the cell called phycobilisomes • Allow cell to capture more light energy than chlorophyll alone

24. Phycobiliproteins and Phycobilisomes Figure 20.10

25. Absorption Spectrum with an Accessory Pigment Figure 20.11

26. 20.4 Anoxygenic Photosynthesis • Anoxygenic photosynthesis is found in at least four phyla of Bacteria • Electron transport reactions occur in the reaction center of anoxygenic phototrophs • Reducing power for CO2 fixation comes from reductants present in the environment (i.e., H2S, Fe2+, or NO2-) • Requires reverse electron transport for NADH production in purple phototrophs

27. Membranes in Anoxygenic Phototrophs Lamellar Membranes in the Purple Bacterium Ectothiorhodospira Chromatophores Figure 20.12

28. Structure of Reaction Center in Purple Bacteria Arrangement of Pigment Molecules in Reaction Center Figure 20.13

29. Structure of Reaction Center in Purple Bacteria Molecular Model of the Protein Structure of the Reaction Center Figure 20.13

30. Example of Electron Flow in Anoxygenic Photosynthesis Figure 20.14

31. Arrangement of Protein Complexes in Reaction Center Figure 20.15

32. Map of Photosynthetic Gene Cluster in Purple Phototroph Figure 20.16

33. Phototrophic Purple and Green Sulfur Bacteria Green Bacterium, Chlorobium limicola Purple Bacterium, Chromatium okenii Figure 20.17

34. Electron Flow in Purple, Green, Sulfur and Heliobacteria Figure 20.18

35. 20.5 Oxygenic Photosynthesis • Oxygenic phototrophs use light to generate ATP and NADPH • The two light reactions are called photosystem I and photosystem II • “Z scheme” of photosynthesis • Photosystem II transfers energy to photosystem I • ATP can also be produced by cyclic photophosphorylation

36. The “Z scheme” in Oxygenic Photosynthesis Figure 20.19

37. II. Autotrophy • 20.6 The Calvin Cycle • 20.7 Other Autotrophic Pathways in Phototrophs

38. 20.6 The Calvin Cycle • The Calvin Cycle • Named for its discoverer Melvin Calvin • Fixes CO2 into cellular material for autotrophic growth • Requires NADPH, ATP, ribulose bisphophate carboxylase (RubisCO), and phosphoribulokinase • 6 molecules of CO2 are required to make 1 molecule of glucose

39. Key Reactions of the Calvin Cycle Figure 20.21a

40. Key Reactions of the Calvin Cycle Figure 20.21b

41. Key Reactions of the Calvin Cycle Figure 20.21c

42. The Calvin Cycle Figure 20.22

43. 20.7 Other Autotrophic Pathways in Phototrophs • Green sulfur bacteria use the reverse citric acid cycle to fix CO2 • Green nonsulfur bacteria use the hydroxyproprionate pathway to fix CO2

44. Autotrophic Pathways in Phototrophic Green Bacteria Figure 20.24a

45. Autotrophic Pathways in Phototrophic Green Bacteria Figure 20.24b

46. III. Chemolithotrophy • 20.8 The Energetics of Chemolithotrophy • 20.9 Hydrogen Oxidation • 20.10 Oxidation of Reduced Sulfur Compounds • 20.11 Iron Oxidation • 20.12 Nitrification • 20.13 Anammox

47. 20.8 The Energetics of Chemolithotrophy • Chemolithotrophs are organisms that obtain energy from the oxidation of inorganic compounds • Mixotrophs are chemolithotrophs that require organic carbon as a carbon source • Many sources of reduced molecules exist in the environment • The oxidation of different reduced compounds yields varying amounts of energy

48. Energy Yields from Oxidation of Inorganic Electron Donors

49. 20.9 Hydrogen Oxidation • Anaerobic H2 oxidizing Bacteria and Archaea are known • Catalyzed by hydrogenase • In the presence of organic compounds such as glucose, synthesis of Calvin cycle and hydrogenase enzymes is repressed

50. Two Hydrogenases of Aerobic H2 Bacteria Figure 20.25