Respiration vs Fermentation: Key Differences, ATP Pathways, and Comparative Insights into Mixed Acid and Butanediol Fermentation

Differences between Respiration and Fermentation:

Features	Respiration	Fermentation
Definition	Respiration refers to the series of biochemical oxidations in which organic molecules are converted to carbon dioxide and water while the chemical energy thus obtained is trapped in a form useful to the cell using exogenous electron acceptor, such as oxygen, nitrate etc. via an electron transport chain.	The process of fermentation uses an endogenous electron acceptor, typically an organic substance (such as pyruvate), to obtain energy from the oxidation of organic materials, such as carbohydrates.
Pathways involved in ATP synthesis	Glycolysis, Kreb’s cycle and Electron Transfer Chain (ETC)	Only Glycolysis
Types	Aerobic and anaerobic respiration	Acetone-butanol-ethanol, Alcohol, Butanediol, Lactic acid, Butyric, Mixed acid, Propionic acid pathways
Need of oxygen	Oxygen needed in aerobic respiration Oxygen not required in anaerobic respiration	Oxygen not necessarily required
Final electron acceptor	Oxygen in aerobic respiration Nitrates, Sulphates, iron compounds in case of anaerobic respiration.	Organic molecules such as pyruvate, acetaldehyde.
Maximum number of ATP produced	In aerobic respiration, 36-38 In anaerobic respiration, 2-36	Maximum number of ATP produced is 2
Electron transport chain	Undergo ETC for ATP generation	Do not undergo ETC for ATP generation
How ATP is generated	By substrate level phosphorylation and oxidative phosphorylation	By substrate level phosphorylation and by reactions such as catalyzed by fumarate reductase and sodium dependent decarboxylase and lactate/H+ symport
Location	Mitochondria and cytoplasm	Cytoplasm
Biproduct	H2O and CO2 with release of ATP in aerobic respiration. C6H12O6 + 602 → 6CO2 + 6H20 + ATP. ATP and lactic acid in animals; ATP, ethanol and CO2 in yeasts	Depends on pathway E.g., in Mixed acid fermentation, Acetic, formic, lactic, and succinic acids; ethanol, CO2, hydrogen gas are end products.
Example	Pseudomonas aeruginosa (aerobic) Paracoccus denitrificans(anaerobic)	Candida albicans

Differences and similarities between anaerobic respiration and fermentation:

The differences between fermentation and anaerobic respiration:

Features	Anaerobic respiration	Fermentation
Definition	Anaerobic respiration is the series of biochemical oxidations in which organic molecules are catabolized while the chemical energy thus obtained is trapped in a form useful to the cell using exogenous electron acceptor such as sulphate, nitrate etc. via an electron transport chain.	Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound (e.g., pyruvate)
TCA involved in ATP generation	Yes	No
ETC involved in ATP generation and generation of Proton Motive Force	Yes	No
Maximum number of ATP generated	Number of ATP generated is 2-36	Maximum number of ATP generated is marginalized i.e. 2
The way of ATP generation	By substrate level phosphorylation by transfer of high energy phosphate bond from high energy phosphate organic intermediates to ADP and oxidative phosphorylation by ETC.	By substrate level phosphorylation and by reactions such as catalyzed by fumarate reductase and sodium dependent decarboxylase and lactate/H+ symport i.e., by ion transport if the energy required for ATP synthesis is less than  -32Kj/MOL
Final electron acceptor	Exogenous electron acceptors (appropriate electron acceptors provided by environment) like NO3–, SO42- etc.	Organic molecules such as pyruvate generated within the organism during cellular processes.
Gain of redox balance	Redox balance obtained by transfer of electrons through specialized electron carriers in ETC.	Redox balance obtained by production and excretion of fermented products from cells. Also in some fermentations, H2 is generated that helps to maintain the redox balance in cell.
Regeneration of NAD+	NAD+ is regenerated by the passing of proton and electron through specialized multiprotein complexes arranged in the Electron Transport System.	NAD+ is regenerated by transfer of electron from NADH to compound like pyruvate. Example: Transfer of electron from NADH to pyruvate to obtain Lactate.
Types of processes	Nitrate reduction, Arsenate reduction, Sulphate reduction, Acetogenesis, Methanogenesis.	Acetone-butanol-ethanol, Alcohol, Butanediol, Lactic acid, Butyric, Mixed acid, Propionic acid pathways
Example:	Paracoccus denitrificans (Nitrate reduction)	Saccharomyces cerevisiae (Ethanol fermentation)

Similarities between anaerobic respiration and fermentation:

• In both processes, there is a catabolism of carbohydrates thereby leading to pyruvate production i.e., EMP is the common glycolytic pathway and the final product of the pathways depend on the type of process.
• Both processes are alternative to aerobic respiration and do not require oxygen.
• Both of the processes occur in cytoplasm.
• Both are essential processes in prokaryotes for energy production and maintenance of redox balance.
• In both the processes, there is an involvement of Substrate level phosphorylation for ATP generation, while other energy harvesting process still exist (Oxidative phosphorylation in Anaerobic respiration and Ion pump in some fermentation depending organisms e.g., Propionigenium modestum which lack Substrate level phosphorylation.

Differences between mixed acid and butanediol fermentation pathways:

Differences between Mixed acid fermentation and 2,3-butanediol fermentation

Features	Mixed acid fermentation	2,3-butanediol fermentation
Organisms performing the process	Mixed-acid fermentation is characteristic of the family Enterobacteriaceae like  Citrobacter, Escherichia, Proteus, Salmonella, Shigella, Yersinia, and Vibrio, and to some species of Aeromonas; it is also carried out by some anaerobic fungi.	2,3-butanediol fermentation(2,3-BDL) is carried out by microorganisms like Enterobacter, Erwinia, Hafnia, Serratia and Klebsiella.
Final product	Monosaccharides, disaccharides, polyalcohol, and, less frequently, polysaccharides can be fermented via the glycolytic pathway, producing lactic, formic, succinic and acetic acids, and ethanol occurring under anaerobic condition. Depending on the bacterial species and growth conditions, the proportions of each product may change. For instance, compared to Enterobacter aerogenes, E. coli produces two to three times as much lactic, succinic, and acetic acid.	Apart from 2,3-BDL and depending on the microorganism and the cultivation conditions, other end products are formed, such as ethanol, acetate, lactate, formate, and succinate as 2,3BDL synthesis is part of a mixed acid fermentation pathway observed under anaerobic or microaerobic growth of different microorganisms.
Ratio of acid: neutral product	Ratio of acid: neutral product is 4:1	Ratio of acid: neutral product is 1:6
Amount of carbon dioxide and hydrogen produced.	Because Formate hydrogen lyase solely produces carbon dioxide from formic acid, the ratio of carbon dioxide to hydrogen is 1:1.	Carbon dioxide to hydrogen ratio is 5:1 because there is carbon dioxide formation from formic acid and two more decarboxylations in the process of acetoin formation.
NADH consumed	4 NADH consumed (2 during ethanol formation, 1 during lactate formation and 1 during succinate formation)	One during formation of 2,3 butanediol from acetoin.
Molecules of Pyruvate used	one	Two