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

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

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

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

Photosynthetic Electron Transport In purple photosynthetic bacteria Fig 5.1

Reaction Center and ATP Synthase Fig 5.2

Photosynthetic Electron Transport In green photosynthetic bacteria Fig 5.5

Photosynthetic Electron Transport In cyanobacteria and chloroplasts Fig 5.7

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

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

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

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.

Propionate Fermentation The Acrylate Pathway Fig 14.3

Propionate Fermentation The Succinate-Propionate Pathway Fig 14.4

Acetate Fermentation Fig 14.5

Lactate Fermentation Homofermentative lactate fermentation

Lactate Fermentation Heterofermentative lactate fermentation Fig 14.6