1. No category

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/bonline/chimes/photo/ebacphot.htm
http://www.ks.uiuc.edu/Research/psu/psu.html