1. Bacterial Physiology (Micr430)
Lecture 4
Photosynthesis and Fermentation Pathways
(Text Chapters: 5, 14)

2. Photosynthesis
Definition: phototrophic or photosynthetic organisms – organisms that obtain most or all of their energy from light.

3. Phototrophic Prokaryotes
Oxygenic phototrophs – most belong to cyanobacteria
Anoxygenic phototrophs
Purple photosynthetic bacteria
Purple sulfur bacteria
Purple non-sulfur bacteria
Green sulfur photosynthetic bacteria
Green non-sulfur photosynthetic bacteria
Heliobacterium

4. Photosynthesis in Bacteria
General scheme
light
Light harvesting
pigments
Reaction
Center
energy DE
Bacteriochlorophyll
is oxidized

5. Photosynthetic Electron Transport
In purple photosynthetic bacteria
Fig 5.1

6. Reaction Center and ATP Synthase
Fig 5.2

7. Photosynthetic Electron Transport
In green photosynthetic bacteria
Fig 5.5

8. Photosynthetic Electron Transport
In cyanobacteria and chloroplasts
Fig 5.7

9. Photosynthetic Electron Transport
In cyanobacteria and chloroplasts
H2O is the electron donor, O2 is evolved
Two light reaction centers
Electron flow is primarily noncyclic, producing both ATP and NADPH

10. Cyanobacteria vs Photosynthetic Bacteria
Cyanobacteria contain chlorophyll a, which is common to all eukaryotic algae and green plants. Water serves as the electron donor and oxygen is generated by photolysis
The purple bacteria contain bacteriochlorphyll a or b, while green bacteria contain bacteriochlorophyll c or d

11. FERMENTATION PATHWAYS
A fermentation is defined as a pathway in which NADH is reoxidized by metabolites produced by the same pathway.
Characteristics:
Reactions usually occur in cytoplasm
ATP is produced via substrate-level phosphorylation
Occurs in the absence of oxygen
Most prevalent in prokaryotes

12. Electron Sink
What to do with electrons generated during oxidation of compounds?
In aerobic organisms, electrons are transported to oxygen or nitrate during respiration
In fermentation, there is no exogenous electron acceptors; the fermentation pathway must produce its own electron acceptors (sinks) because they have to dispose of electrons generated during oxidation.

13. Propionate Fermentation
The Acrylate Pathway
Fig 14.3

14. Propionate Fermentation
The Succinate-Propionate Pathway
Fig 14.4

15. Acetate Fermentation
Fig 14.5

16. Lactate Fermentation
Homofermentative lactate fermentation

17. Lactate Fermentation
Heterofermentative
lactate
fermentation
Fig 14.6