What are the 4 unifying themes of fermentation?
- O2 is not needed
- Electron acceptor is usually either pyruvate or pyruvate derivative
- NADH must be oxidized to NAD+ without an ETC
- ATP yield per glucose is significantly reduced (no ETC)
Define fermentation.
A pathway in which NADH is reoxidized by metabolites produced by the pathway
What are fermentations named after?
The major end products they generate
What are the 6 main classes of carbohydrate fermentations?
- Lactic
- Ethanol
- Butyric
- Mixed acid
- Propionic
- Homoacetic
Why are strict anaerobes killed by oxygen?
- Toxic products of oxygen reduction are produced when single electrons are added to oxygen sequentially
- These toxic products accumulate in the cell
What toxic products are produced by oxygen reduction?
- Hydroxyl radical (OH•)
- Superoxide radical (O2-)
- Hydrogen peroxide (H2O2)
Why don’t aerobic and aerotolerant organisms acumulate superoxide radicals or hydrogen peroxide, but strict anaerobes do?
- Aerobes/aerotolerants have superoxide disumutase and catalase
- Strict anaerobes don’t have these enzymes that break down the toxic products
What reaction does superoxide dismutase catalyze?
O2- + O2- + 2H2 –> H2O2 + O2
What reaction does catalase catalyze?
H2O2 + H2O2 –> 2H2O + O2
How do most fermenting bacteria make most or all of their ATP?
Substrate-level phosphorylations
How do anaerobes generate a Δp (needed for solute transport, motility, etc.)?
- Reversing membrane-bound ATPase
- Reducing fumarate
- Carrying out a periplasmic oxidation of electron donors
- W. succinogenes
Explain what is happening in the figure (energy conservation in anaerobic bacteria).
Fermentation pathways themselves produce the electron acceptors for the electrons produced during oxidations. What are these electron acceptors called?
Electron sinks
- Because they dispose of the electrons removed during the oxidations
- The reduced products are excreted into the medium
What are fermentation processes categorized by? (as in what is their defining characteristic)
Excretion of large quantities of reduced organic compounds (alcohols, organic acids, solvents, hydrogen gas)
What is the anaerobic food chain?
The fermentation of amino acids, carbs, purines, and pyrimidines to organic acids and alcohols and the conversion of these compounds to CO2/CH4/H2
- By prokaryotes
What is the importance of the anaerobic food chain in the carbon cycle?
Regenerates gaseous carbon
Some anaerobic bacteria use protons as the major electron sink. They include _____.
obligate proton-reducing acetogens
Define/describe lactic acid bacteria.
A heterogeneous group of aerotolerant anaerobes that ferment glucose to lactate as the sole or major product of fermentation
Lactic acid bacteria include what genera?
- Lactobacillus
- Sporolactobacillus
- Streptococcus
- Leuconostoc
- Pediococcus
- Bifidobacterium
Where are lactic acid bacteria found?
- Living on the skin of animals, in the gastrointestinal tract, and in other place (e.g. mouth and throat)
- Some genera live in vegetation and in dairy products
Lactic acid bacteria metabolize glucose only fermentatively and derive most of their ATP from ____.
substrate-level phosphorylation
What are the 2 major types of lactate fermentation? What glucose metabolism pathway does each one use?
- Homofermentative
- Glycolysis - Heterofermentative
- PPP
What is the only product of homolactate fermenation?
Lactate
In homolactate fermentation, bacteria use what pathway to oxidize glucose to pyruvate?
Glycolytic pathway
