1. Photosynthesis in Bacteria
By Emmy Muscan

2. Overview What is Photosynthesis General mechanism of Photosynthesis
Classification of Photosynthetic Bacteria
Oxygenic Photosynthesis
Anoxygenic Photosynthesis
Conclusion
References

3. What is Photosynthesis?
Conversion of light energy to chemical energy
Net equation:
6CO2+12H2O+LightEnergyC6H12O6+6O2+6H20
Photosynthetic reactions divided into two stages:
-light reactions- light energy absorbed & converted to chemical energy (ATP, NADPH)
-dark reactions-carbohydrates made from CO2 using energy stored in ATP & NADPH

4. General Mechanism of Bacterial Photosynthesis
Light-harvesting pigments (LHPs) embedded in membranes capture light energy and transfer it to a protein-complex called a reaction center
the energy is converted into excited, low potential electrons
electrons are fed into an electron transport chain, where they "fall" through a series of electron carriers, generating a proton motive force
membrane-bound ATPases then use the proton motive force to make ATP.

6. Classification of Photosynthetic Bacteria
Five photosynthetic groups within domain Bacteria (based on 16S rRNA)
Oxygenic Photosynthesis
Cyanobacteria and prochlorophytes
Anoxygenic Photosynthesis
Purple bacteria
Green sulfur bacteria
Heliobacteria
Green gliding bacteria

7. Oxygenic Photosynthesis
Occurs in cyanobacteria and prochlorophytes
Synthesis of carbohydrates results in release of molecular O2 and removal of CO2 from atmoshphere
Occurs in lamallae which house thylakoids containing chlorophyll a/b and phycobilisomes pigments which gather light energy
Uses two photosystems (PS):
- PS II- generates a proton-motive force for making ATP
- PS I- generates low potential electrons for reducing power.

8. Oxygenic Photosynthesis cont.

9. Anoxygenic Photosynthesis
Uses light energy to create organic compounds, and sulfur or fumarate compounds instead of O2
Occurs in purple bacteria, green sulfur bacteria, green gliding bacteria and heliobacteria
Uses bacteriochlorophyll pigments instead of chlorophyll
Uses one photosystem (PS I) to generate ATP in “cyclic” manner

10. Anoxygenic Photosynthesis cont.

11. Comparison of electron transport pathways in oxygenic and anoxygenic photosynthesis

12. Chlorophyll Bacteriochlorophyll
                

13. Conclusion
Photosynthesis is the conversion of light energy into chemical energy
Photosynthesis in bacteria is divided into “light” and “dark” reactions
Oxygenic photosynthesis occurs in cyanobacteria and uses PS I and PS II, chlorophyll and phycobilisome pigments
Anoxygenic photosynthesis occurs in all the other bacteria and each species has one reaction center (PS I); uses bacteriochlorophyll pigments

14. References Briggs, W. (ed.) 1989. Photosynthesis. Alan Liss., N.Y.
Staley J.T. and Reysenbach A., (ed.) Biodiversity of Microbial Life,”Evolution and Diversity of Photosynthetic Prokaryotes” Beverly K. Pierson Wiley-Liss, Inc. New York, 2002.