8.4 Fermentation
2 min read•june 18, 2024
is a crucial metabolic process that allows microorganisms to survive without oxygen. It breaks down organic compounds, usually carbohydrates, in the cell's cytoplasm, producing ATP and various end products like or .
Different pathways exist, each with unique products and applications. is key in dairy production, while ethanol fermentation is vital for brewing. Understanding these pathways helps explain microbial survival in diverse environments and their industrial uses.
Fermentation
Process of oxygen-independent fermentation
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- Breaks down organic compounds, usually carbohydrates (glucose), without oxygen
- Takes place in the cytoplasm of cells
- Produces ATP via
- Functions independently of oxygen as it does not rely on the electron transport chain or
- Enables organisms to survive in anaerobic environments (deep sea vents, soil)
- Generates less ATP compared to aerobic respiration, typically 2 ATP per glucose molecule
- Results in various end products based on the specific pathway and microorganism (ethanol, lactic acid, organic acids)
Key fermentation pathways and products
- pathway
- enzyme reduces to lactic acid
- Regenerates to allow to proceed
- Used by lactic acid bacteria (, )
- Essential in dairy fermentations (, , kefir)
- Ethanol fermentation pathway
- Pyruvate undergoes decarboxylation to form , then reduction to ethanol
- Regenerates NAD+ to sustain glycolysis
- Employed by yeasts ()
- Crucial in beer and wine production
- Produces as a byproduct
- pathway
- Yields a combination of organic acids (acetic, lactic, succinic) and ethanol
- Utilized by Enterobacteriaceae (Escherichia coli)
- Butanediol fermentation pathway
- Generates , ethanol, and CO2 as end products
- Carried out by certain Enterobacteriaceae species (Klebsiella pneumoniae)
Fermentation vs anaerobic respiration
- Fermentation
- Occurs without an external electron acceptor (oxygen)
- Uses organic compounds as both electron donors and acceptors
- Produces organic end products (ethanol, lactic acid)
- Generates ATP only through
- Anaerobic respiration
- Employs an external electron acceptor other than oxygen (nitrate, sulfate)
- Involves an electron transport chain
- Typically yields inorganic end products (nitrite, sulfide)
- Generates ATP via both substrate-level phosphorylation and oxidative phosphorylation
- Produces more ATP than fermentation but less than aerobic respiration
Metabolic considerations in fermentation
- play a crucial role in fermentation pathways
- NADH is oxidized to NAD+ during fermentation, allowing glycolysis to continue
- can switch between fermentation and aerobic respiration depending on oxygen availability
- rely solely on fermentation or anaerobic respiration for energy production
- Fermentation is one of several used by microorganisms for energy generation
Key Terms to Review (52)
2,3-Butanediol: 2,3-Butanediol is a colorless, viscous liquid organic compound with the chemical formula C4H10O2. It is a valuable byproduct of fermentation processes, particularly in the context of microbial metabolism and biofuel production.
Acetaldehyde: Acetaldehyde is a volatile, flammable, and colorless organic compound with the chemical formula CH3CHO. It is an important intermediate in the metabolism of ethanol and is produced during the fermentation process.
Acetic Acid: Acetic acid is a colorless, pungent liquid that is the main component of vinegar. It is a weak organic acid that is produced naturally during the fermentation of carbohydrates by certain bacteria and is also synthesized industrially for various applications.
Acetone: Acetone is a volatile, flammable organic solvent with the chemical formula C3H6O. It is commonly produced by microbial fermentation and used in various industrial applications.
Acetone-butanol-ethanol fermentation: Acetone-butanol-ethanol (ABE) fermentation is a biological process in which certain bacteria convert sugars into acetone, butanol, and ethanol. This process is often carried out by Clostridium species under anaerobic conditions.
Alcohol Dehydrogenase: Alcohol dehydrogenase (ADH) is an enzyme that catalyzes the oxidation of alcohols to aldehydes or ketones, playing a crucial role in the metabolism of alcohol in the body. It is primarily found in the liver and is responsible for the first step in the breakdown of ethanol, converting it to acetaldehyde.
Alcohol fermentation: Alcohol fermentation is a biological process by which sugars such as glucose are converted into ethanol and carbon dioxide by the action of yeast or bacteria. It occurs under anaerobic conditions.
Alcoholic Fermentation: Alcoholic fermentation is a metabolic process in which sugars, such as glucose and fructose, are converted into ethanol and carbon dioxide by certain microorganisms, particularly yeast. This process is central to the production of alcoholic beverages and has been utilized by our ancestors for centuries.
API strips: API strips are a tool used in microbiology to identify bacteria through biochemical tests. Each strip contains multiple wells with dehydrated substrates that react with bacterial metabolic products.
ATP (Adenosine Triphosphate): ATP, or adenosine triphosphate, is the primary energy currency of the cell. It is a high-energy molecule that stores and transports chemical energy within living organisms, powering a wide range of cellular processes. ATP is central to the fundamental mechanisms of life, as it is involved in various metabolic pathways, including carbohydrate metabolism, cellular respiration, and photosynthesis.
Biofuel: Biofuel is a type of energy source derived from organic material, such as plant or animal waste. It is produced through biochemical processes including fermentation by microbes.
Biofuel Production: Biofuel production is the process of generating fuels from renewable biological sources, such as plants and microorganisms. These biofuels can be used as alternatives to traditional fossil fuels, offering a more sustainable and environmentally-friendly energy source.
Butanol: Butanol is a four-carbon alcohol produced by certain bacteria through the fermentation of sugars. It serves as both an industrial solvent and a biofuel.
Carbon Dioxide: Carbon dioxide is a colorless, odorless gas that is produced as a byproduct of various metabolic and combustion processes. It is a vital component in the natural carbon cycle and plays a crucial role in the processes of fermentation and photosynthesis.
Cheese: Cheese is a dairy product derived from milk that undergoes fermentation by specific bacteria and molds. The metabolic activities of these microorganisms are crucial for the development of cheese's flavor, texture, and nutritional properties.
Embden-Meyerhof Pathway: The Embden-Meyerhof pathway, also known as glycolysis, is a fundamental metabolic process that converts glucose into pyruvate, generating a small amount of ATP in the process. This pathway is a crucial component of cellular respiration and fermentation, providing energy for various cellular functions.
Embden-Meyerhof-Parnas pathway: The Embden-Meyerhof-Parnas (EMP) pathway, also known as glycolysis, is a series of enzymatic reactions that convert glucose into pyruvate, generating ATP and NADH in the process. This pathway is fundamental for energy production in both aerobic and anaerobic organisms.
Ethanol: Ethanol, also known as ethyl alcohol or grain alcohol, is a colorless, volatile, flammable liquid that is the primary type of alcohol found in alcoholic beverages. It is produced through the fermentation of sugars by yeast and has a wide range of applications, from being a fuel source to a disinfectant and preservative.
Ethanol is closely tied to the topics of 1.1 What Our Ancestors Knew, 8.2 Catabolism of Carbohydrates, 8.4 Fermentation, 13.1 Controlling Microbial Growth, and 13.3 Using Chemicals to Control Microorganisms. Its production, properties, and uses are integral to understanding these key concepts in microbiology.
Facultative Anaerobes: Facultative anaerobes are microorganisms that can grow and survive in the presence or absence of oxygen. They have the ability to switch between aerobic respiration, which uses oxygen, and anaerobic respiration or fermentation, which does not require oxygen. This flexibility allows them to thrive in a variety of environments with varying oxygen levels.
Fermentation: Fermentation is a metabolic process that converts sugar to acids, gases, or alcohol in the absence of oxygen. It is commonly used by microorganisms like yeast and bacteria.
Fermentation: Fermentation is a metabolic process in which an organism converts carbohydrates, such as sugars, into acids, gases, or alcohol. It is a crucial biological process that has been utilized by our ancestors for centuries and continues to play a vital role in various aspects of microbiology, from the production of food and beverages to the generation of energy in certain microorganisms.
The term 'fermentation' connects to the topics of 1.1 What Our Ancestors Knew, 1.3 Types of Microorganisms, 4.1 Prokaryote Habitats, Relationships, and Microbiomes, 8.2 Catabolism of Carbohydrates, 8.3 Cellular Respiration, 8.4 Fermentation, and 9.2 Oxygen Requirements for Microbial Growth, as it represents an ancient and widely-employed metabolic strategy employed by diverse microorganisms to derive energy from organic compounds in the absence of oxygen or under limited oxygen conditions.
Food Preservation: Food preservation refers to the various methods and techniques used to extend the shelf-life and maintain the quality of food products. It involves the application of physical, chemical, or biological processes to prevent or slow down the deterioration of food caused by microbial growth, enzymatic reactions, and environmental factors.
Glycolysis: Glycolysis is the metabolic pathway that converts glucose, a six-carbon sugar, into two molecules of pyruvate, a three-carbon compound. This process is the first stage of cellular respiration and occurs in the cytoplasm of cells, providing a crucial source of energy for the cell.
Heterolactic fermentation: Heterolactic fermentation is a metabolic process in which glucose is converted into lactate, ethanol, and carbon dioxide. It involves multiple pathways including the pentose phosphate pathway.
Homolactic fermentation: Homolactic fermentation is a metabolic process by which glucose is converted into lactic acid with the generation of ATP. This process occurs in some bacteria and muscle cells under anaerobic conditions.
Lactase: Lactase is an enzyme produced in the small intestine that is responsible for breaking down the milk sugar lactose into its simpler components, glucose and galactose, which can then be absorbed by the body. This process is essential for the digestion and utilization of lactose, a key nutrient found in dairy products.
Lactate Dehydrogenase: Lactate dehydrogenase (LDH) is an enzyme that catalyzes the interconversion of lactate and pyruvate, playing a crucial role in cellular energy metabolism, particularly during anaerobic glycolysis. It is found in various tissues and is commonly used as a biomarker for certain medical conditions.
Lactic Acid: Lactic acid is a chemical compound produced during the metabolic process of anaerobic glycolysis, where glucose is broken down to generate energy in the absence of oxygen. It plays a crucial role in various biological processes and is particularly relevant in the context of our ancestors' knowledge, fermentation, and the anatomy and normal microbiota of the urogenital tract.
Lactic acid bacteria (LAB): Lactic acid bacteria (LAB) are a group of Gram-positive bacteria that ferment sugars into lactic acid. They play a crucial role in food fermentation and are important in various industrial applications.
Lactic acid fermentation: Lactic acid fermentation is a metabolic process by which glucose or other sugars are converted into cellular energy and the metabolite lactate. This anaerobic process occurs in the absence of oxygen and is utilized by certain bacteria, fungi, and animal muscle cells.
Lactic Acid Fermentation: Lactic acid fermentation is a metabolic process in which glucose or other sugars are converted into lactic acid as the end product, typically occurring in the absence of oxygen. This anaerobic process is an important part of cellular respiration and is commonly observed in certain bacteria and in the muscle cells of animals.
Lactobacillus: Lactobacillus is a genus of Gram-positive bacteria known for their role in fermenting sugars into lactic acid. They are commonly found in the human gut, mouth, and urogenital tract, playing a crucial role in maintaining health.
Leuconostoc: Leuconostoc is a genus of Gram-positive bacteria known for its role in fermentation processes. It is commonly found in dairy products and plant material.
Meningitis: Meningitis is an inflammation of the protective membranes covering the brain and spinal cord, known as the meninges. It can be caused by bacterial, viral, fungal, or parasitic infections.
Metabolic Pathways: Metabolic pathways are a series of interconnected chemical reactions that occur within cells to sustain life. These pathways are responsible for the breakdown and synthesis of molecules, providing the energy and building blocks necessary for cellular processes and organismal function. Metabolic pathways are central to the topics of 7.5 Using Biochemistry to Identify Microorganisms and 8.4 Fermentation, as they underlie the biochemical mechanisms that allow microorganisms to be characterized and utilize different energy sources.
Mixed acid fermentation: Mixed acid fermentation is a metabolic process by which bacteria convert sugars into a mixture of acids, gases, and other products. It is typical in certain enteric bacteria such as Escherichia coli.
NAD+: NAD+, or nicotinamide adenine dinucleotide, is a coenzyme found in all living cells. It is essential for numerous metabolic processes, serving as an electron carrier in redox reactions that are crucial for energy production and various other cellular functions.
Obligate Anaerobes: Obligate anaerobes are microorganisms that can only survive and grow in the complete absence of oxygen. They are unable to carry out aerobic respiration and instead rely on fermentation or other anaerobic metabolic pathways to generate energy, making them dependent on anaerobic conditions for their survival.
Oxidative phosphorylation: Oxidative phosphorylation is the process by which cells generate ATP through the electron transport chain and chemiosmosis in the mitochondria. It is the final stage of cellular respiration, involving oxygen as the final electron acceptor.
Propionic acid fermentation: Propionic acid fermentation is a type of fermentation process carried out by certain bacteria that convert carbohydrates into propionic acid, acetic acid, and CO₂. This type of fermentation is commonly seen in the production of Swiss cheese.
Pyruvate: Pyruvate is a key metabolic intermediate produced during the breakdown of glucose and other carbohydrates. It serves as a central molecule in several important cellular processes, including cellular respiration and fermentation.
Pyruvate decarboxylase: Pyruvate decarboxylase is an enzyme that catalyzes the decarboxylation of pyruvate to acetaldehyde and carbon dioxide. It plays a crucial role in the fermentation process, particularly in yeast and other microorganisms.
Pyruvate Decarboxylase: Pyruvate decarboxylase is an enzyme that catalyzes the decarboxylation of pyruvate, a key intermediate in cellular respiration, to produce acetaldehyde and carbon dioxide. This enzymatic reaction is a crucial step in the fermentation process, allowing organisms to generate energy anaerobically.
Redox Reactions: Redox (reduction-oxidation) reactions are a fundamental class of chemical reactions where the transfer of electrons between reactants occurs. These reactions involve the loss of electrons (oxidation) and the gain of electrons (reduction), which are coupled processes essential for many biological and chemical processes.
Saccharomyces cerevisiae: Saccharomyces cerevisiae is a species of yeast commonly used in baking, brewing, and scientific research. It plays a crucial role in fermentation processes, converting sugars into ethanol and carbon dioxide.
Staphylococcus aureus: Staphylococcus aureus is a Gram-positive bacterium commonly found on the skin and in the nasal passages. It can cause a range of infections from minor skin conditions to severe diseases like pneumonia and sepsis.
Streptococcus: Streptococcus is a genus of Gram-positive bacteria that often occur in chains or pairs. They are known for causing a variety of infections in humans, ranging from mild throat infections to life-threatening diseases.
Substrate-level phosphorylation: Substrate-level phosphorylation is a metabolic process for generating ATP by the direct transfer of a phosphate group to ADP from an intermediate substrate. This occurs in the cytoplasm during glycolysis and in the mitochondrial matrix during the Krebs cycle.
Substrate-Level Phosphorylation: Substrate-level phosphorylation is a metabolic process in which the energy released from a chemical reaction is used to directly transfer a phosphate group to a molecule, resulting in the production of ATP without the involvement of the electron transport chain or oxidative phosphorylation. This process is a key step in both cellular respiration and fermentation pathways.
Succinic Acid: Succinic acid is a dicarboxylic acid that is an important intermediate in the citric acid cycle, a key metabolic pathway involved in cellular respiration and energy production. It is also a valuable chemical compound with various industrial and commercial applications.
Yogurt: Yogurt is a dairy product produced by bacterial fermentation of milk. The bacteria used to make yogurt are known as yogurt cultures.
Zymase: Zymase is an enzyme complex found in yeast cells that catalyzes the conversion of sugar (glucose) into ethanol and carbon dioxide through the process of fermentation. It is a crucial component in the metabolic pathway of anaerobic respiration, allowing yeast to generate energy in the absence of oxygen.