Bacterial Physiology (Micr430)

Lecture 4Photosynthesis 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 BacteriaGeneral scheme

Light harvestingpigments

light

energyReactionCenter

Bacteriochlorophyllis oxidized

E

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 FermentationHomofermentative lactate fermentation

Lactate Fermentation

Heterofermentativelactate

fermentation

Fig 14.6