Photosynthesis in Bacteria By Emmy Muscan

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

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

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.

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

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.

Oxygenic Photosynthesis cont.

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

Anoxygenic Photosynthesis cont.

Comparison of electron transport pathways in oxygenic and anoxygenic photosynthesis

Chlorophyll Bacteriochlorophyll                 

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

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. http://www.biologie.uni-hamburg.de/b-online/chimes/photo/ebacphot.htm http://www.ks.uiuc.edu/Research/psu/psu.html