Review Fermentation by Filling in the Blanks Below

Learning Objectives

• Define fermentation and explicate why it does non crave oxygen
• Describe the fermentation pathways and their end products and give examples of microorganisms that utilize these pathways
• Compare and contrast fermentation and anaerobic respiration

Many cells are unable to deport out respiration because of 1 or more than of the following circumstances:

1. The cell lacks a sufficient amount of any advisable, inorganic, final electron acceptor to deport out cellular respiration.
2. The cell lacks genes to make appropriate complexes and electron carriers in the electron transport organisation.
3. The cell lacks genes to make ane or more enzymes in the Krebs cycle.

Whereas lack of an appropriate inorganic final electron acceptor is environmentally dependent, the other two atmospheric condition are genetically determined. Thus, many prokaryotes, including members of the clinically important genus Streptococcus, are permanently incapable of respiration, even in the presence of oxygen. Conversely, many prokaryotes are facultative, significant that, should the ecology atmospheric condition modify to provide an advisable inorganic concluding electron acceptor for respiration, organisms containing all the genes required to do and then will switch to cellular respiration for glucose metabolism because respiration allows for much greater ATP product per glucose molecule.

If respiration does not occur, NADH must be reoxidized to NAD⁺ for reuse equally an electron carrier for glycolysis, the cell'south only mechanism for producing whatever ATP, to proceed. Some living systems utilise an organic molecule (commonly pyruvate) equally a final electron acceptor through a process called fermentation. Fermentation does not involve an electron ship system and does not straight produce any additional ATP beyond that produced during glycolysis past substrate-level phosphorylation. Organisms carrying out fermentation, called fermenters, produce a maximum of two ATP molecules per glucose during glycolysis. Table 1 compares the last electron acceptors and methods of ATP synthesis in aerobic respiration, anaerobic respiration, and fermentation. Annotation that the number of ATP molecules shown for glycolysis assumes the Embden-Meyerhof-Parnas pathway. The number of ATP molecules made by substrate-level phosphorylation (SLP) versus oxidative phosphorylation (OP) are indicated.

Table 1. Comparison of Respiration Versus Fermentation
Blazon of Metabolism	Instance	Final Electron Acceptor	Pathways Involved in ATP Synthesis (Blazon of Phosphorylation)	Maximum Yield of ATP Molecules
Aerobic respiration	Pseudomonas aeruginosa	[latex]{\text{O}}_{2}[/latex]	EMP glycolysis (SLP) Krebs cycle (SLP) Electron transport and chemiosmosis (OP):	2 2 34
			Full	38
Anaerobic respiration	Paracoccus denitrificans	[latex]{{\text{NO}}_{3}}^{-},{\text{SO}}_{four}^{-2},{\text{Fe}}^{+iii},{\text{CO}}_{2}[/latex], other inorganics	EMP glycolysis (SLP) Krebs bicycle (SLP) Electron transport and chemiosmosis (OP):	2 2 i–32
			Total	v–36
Fermentation	Candida albicans	Organics (commonly pyruvate)	EMP glycolysis (SLP) Fermentation	2 0
			Total	2

Microbial fermentation processes have been manipulated by humans and are used extensively in the product of various foods and other commercial products, including pharmaceuticals. Microbial fermentation tin also be useful for identifying microbes for diagnostic purposes.

Fermentation by some bacteria, like those in yogurt and other soured food products, and past animals in muscles during oxygen depletion, is lactic acid fermentation. The chemic reaction of lactic acid fermentation is as follows:

[latex]\text{Pyruvate + NADH}\text{ }\stackrel{}{\leftrightarrow }\text{ }{\text{lactic acrid + NAD}}^{\text{+}}[/latex]

Leaner of several gram-positive genera, including Lactobacillus , Leuconostoc , and Streptococcus , are collectively known equally the lactic acid bacteria (LAB), and various strains are important in food production. During yogurt and cheese production, the highly acidic surroundings generated by lactic acid fermentation denatures proteins contained in milk, causing it to solidify. When lactic acrid is the only fermentation product, the process is said to be homolactic fermentation; such is the case for Lactobacillus delbrueckii and S. thermophiles used in yogurt product. Notwithstanding, many bacteria perform heterolactic fermentation, producing a mixture of lactic acrid, ethanol and/or acetic acrid, and CO₂ as a result, because of their use of the branched pentose phosphate pathway instead of the EMP pathway for glycolysis. Ane important heterolactic fermenter is Leuconostoc mesenteroides, which is used for souring vegetables like cucumbers and cabbage, producing pickles and sauerkraut, respectively.

Lactic acrid bacteria are also important medically. The production of depression pH environments within the body inhibits the establishment and growth of pathogens in these areas. For example, the vaginal microbiota is equanimous largely of lactic acrid leaner, but when these leaner are reduced, yeast can proliferate, causing a yeast infection. Additionally, lactic acid bacteria are important in maintaining the health of the gastrointestinal tract and, as such, are the chief component of probiotics.

Another familiar fermentation process is alcohol fermentation, which produces ethanol. The ethanol fermentation reaction is shown in Figure 1. In the commencement reaction, the enzyme pyruvate decarboxylase removes a carboxyl group from pyruvate, releasing CO₂ gas while producing the ii-carbon molecule acetaldehyde. The second reaction, catalyzed by the enzyme alcohol dehydrogenase, transfers an electron from NADH to acetaldehyde, producing ethanol and NAD⁺. The ethanol fermentation of pyruvate by the yeast Saccharomyces cerevisiae is used in the product of alcoholic beverages and also makes bread products rise due to CO_ii production. Outside of the nutrient manufacture, ethanol fermentation of plant products is of import in biofuel product.

Figure 1. The chemical reactions of booze fermentation are shown here. Ethanol fermentation is of import in the product of alcoholic beverages and bread.

Beyond lactic acrid fermentation and alcohol fermentation, many other fermentation methods occur in prokaryotes, all for the purpose of ensuring an adequate supply of NAD⁺ for glycolysis (Table two). Without these pathways, glycolysis would not occur and no ATP would exist harvested from the breakdown of glucose. It should exist noted that near forms of fermentation also homolactic fermentation produce gas, commonly CO₂ and/or hydrogen gas. Many of these dissimilar types of fermentation pathways are too used in food production and each results in the product of different organic acids, contributing to the unique flavor of a particular fermented food product. The propionic acid produced during propionic acid fermentation contributes to the distinctive flavor of Swiss cheese, for case.

Several fermentation products are important commercially exterior of the food industry. For example, chemical solvents such as acetone and butanol are produced during acetone-butanol-ethanol fermentation. Complex organic pharmaceutical compounds used in antibiotics (due east.g., penicillin), vaccines, and vitamins are produced through mixed acid fermentation. Fermentation products are used in the laboratory to differentiate diverse leaner for diagnostic purposes. For instance, enteric bacteria are known for their ability to perform mixed acid fermentation, reducing the pH, which tin be detected using a pH indicator. Similarly, the bacterial production of acetoin during butanediol fermentation can also be detected. Gas product from fermentation can as well be seen in an inverted Durham tube that traps produced gas in a broth culture.

Microbes can as well exist differentiated co-ordinate to the substrates they can ferment. For instance, E. coli can ferment lactose, forming gas, whereas some of its close gram-negative relatives cannot. The ability to ferment the sugar booze sorbitol is used to place the pathogenic enterohemorrhagic O157:H7 strain of E. coli because, unlike other East. coli strains, information technology is unable to ferment sorbitol. Last, mannitol fermentation differentiates the mannitol-fermenting Staphylococcus aureus from other not–mannitol-fermenting staphylococci.

Tabular array 2. Common Fermentation Pathways
Pathway	End Products	Example Microbes	Commercial Products
Acetone-butanol-ethanol	Acetone, butanol, ethanol, CO2	Clostridium acetobutylicum	Commercial solvents, gasoline alternative
Alcohol	Ethanol, CO2	Candida, Saccharomyces	Beer, breadstuff
Butanediol	Formic and lactic acid; ethanol; acetoin; 2,3 butanediol; CO2; hydrogen gas	Klebsiella, Enterobacter	Chardonnay vino
Butyric acid	Butyric acrid, CO2, hydrogen gas	Clostridium butyricum	Butter
Lactic acid	Lactic acid	Streptococcus, Lactobacillus	Sauerkraut, yogurt, cheese
Mixed acid	Acetic, formic, lactic, and succinic acids; ethanol, COii, hydrogen gas	Escherichia, Shigella	Vinegar, cosmetics, pharmaceuticals
Propionic acrid	Acetic acid, propionic acid, COii	Propionibacterium, Bifidobacterium	Swiss cheese

Think about Information technology

• When would a metabolically versatile microbe perform fermentation rather than cellular respiration?

Identifying Leaner past Using API Exam Panels

Identification of a microbial isolate is essential for the proper diagnosis and advisable treatment of patients. Scientists have developed techniques that place leaner according to their biochemical characteristics. Typically, they either examine the use of specific carbon sources every bit substrates for fermentation or other metabolic reactions, or they identify fermentation products or specific enzymes present in reactions. In the past, microbiologists take used individual test tubes and plates to conduct biochemical testing. However, scientists, especially those in clinical laboratories, now more frequently use plastic, disposable, multitest panels that contain a number of miniature reaction tubes, each typically including a specific substrate and pH indicator. After inoculation of the test panel with a small sample of the microbe in question and incubation, scientists can compare the results to a database that includes the expected results for specific biochemical reactions for known microbes, thus enabling rapid identification of a sample microbe. These test panels have allowed scientists to reduce costs while improving efficiency and reproducibility by performing a larger number of tests simultaneously.

Many commercial, miniaturized biochemical test panels cover a number of clinically important groups of bacteria and yeasts. One of the earliest and most popular test panels is the Analytical Profile Alphabetize (API) panel invented in the 1970s. Once some bones laboratory characterization of a given strain has been performed, such as determining the strain'southward Gram morphology, an appropriate exam strip that contains 10 to 20 different biochemical tests for differentiating strains inside that microbial group can be used. Currently, the various API strips can be used to speedily and easily identify more than 600 species of bacteria, both aerobic and anaerobic, and approximately 100 unlike types of yeasts. Based on the colors of the reactions when metabolic end products are nowadays, due to the presence of pH indicators, a metabolic contour is created from the results (Effigy 2). Microbiologists can and so compare the sample's profile to the database to identify the specific microbe.

Effigy two. The API 20NE test strip is used to identify specific strains of gram-negative leaner outside the Enterobacteriaceae. Here is an API 20NE test strip result for Photobacterium damselae ssp. piscicida.

Clinical Focus: Alex, Part 2

This case continues Alex's story that started in Energy Matter and Enzymes.

Many of Alex's symptoms are consequent with several unlike infections, including influenza and pneumonia. Nonetheless, his sluggish reflexes forth with his light sensitivity and stiff neck suggest some possible involvement of the central nervous system, perchance indicating meningitis. Meningitis is an infection of the cerebrospinal fluid (CSF) around the encephalon and spinal cord that causes inflammation of the meninges, the protective layers covering the brain. Meningitis can be acquired by viruses, bacteria, or fungi. Although all forms of meningitis are serious, bacterial meningitis is specially serious. Bacterial meningitis may be caused by several different bacteria, but the bacterium Neisseria meningitidis , a gram-negative, edible bean-shaped diplococcus, is a common crusade and leads to death inside 1 to 2 days in 5% to 10% of patients.

Given the potential seriousness of Alex'south weather condition, his md advised his parents to take him to the hospital in the Gambian capital of Banjul and there take him tested and treated for possible meningitis. After a 3-hour drive to the hospital, Alex was immediately admitted. Physicians took a blood sample and performed a lumbar puncture to test his CSF. They as well immediately started him on a course of the antibody ceftriaxone, the drug of choice for treatment of meningitis caused by Northward. meningitidis, without waiting for laboratory exam results.

• How might biochemical testing exist used to confirm the identity of N. meningitidis?
• Why did Alex's doctors decide to administrate antibiotics without waiting for the test results?

We'll render to Alex's case in later pages.

Key Concepts and Summary

• Fermentation uses an organic molecule every bit a final electron acceptor to regenerate NAD⁺ from NADH then that glycolysis tin can continue.
• Fermentation does not involve an electron send system, and no ATP is made by the fermentation procedure direct. Fermenters make very piddling ATP—only two ATP molecules per glucose molecule during glycolysis.
• Microbial fermentation processes have been used for the production of foods and pharmaceuticals, and for the identification of microbes.
• During lactic acrid fermentation, pyruvate accepts electrons from NADH and is reduced to lactic acid. Microbes performing homolactic fermentation produce only lactic acid as the fermentation production; microbes performing heterolactic fermentation produce a mixture of lactic acid, ethanol and/or acetic acrid, and CO₂.
• Lactic acid production by the normal microbiota prevents growth of pathogens in certain body regions and is of import for the health of the gastrointestinal tract.
• During ethanol fermentation, pyruvate is first decarboxylated (releasing CO_ii) to acetaldehyde, which and then accepts electrons from NADH, reducing acetaldehyde to ethanol. Ethanol fermentation is used for the production of alcoholic beverages, for making bread products rise, and for biofuel production.
• Fermentation products of pathways (e.m., propionic acid fermentation) provide distinctive flavors to nutrient products. Fermentation is used to produce chemic solvents (acetone-butanol-ethanol fermentation) and pharmaceuticals (mixed acid fermentation).
• Specific types of microbes may exist distinguished by their fermentation pathways and products. Microbes may as well be differentiated according to the substrates they are able to ferment.

Multiple Choice

Which of the following is the purpose of fermentation?

1. to brand ATP
2. to brand carbon molecule intermediates for anabolism
3. to make NADH
4. to brand NAD⁺

Bear witness Respond

Answer d. The purpose of fermentation is to brand NAD⁺.

Which molecule typically serves every bit the final electron acceptor during fermentation?

1. oxygen
2. NAD⁺
3. pyruvate
4. CO₂

Show Answer

Respond c. Pyruvate typically serves every bit the final electron acceptor during fermentation.

Which fermentation product is important for making staff of life rise?

1. ethanol
2. CO_two
3. lactic acid
4. hydrogen gas

Show Respond

Answer b. CO₂ is important for making bread ascent.

Which of the post-obit is not a commercially important fermentation product?

1. ethanol
2. pyruvate
3. butanol
4. penicillin

Show Answer

Answer b. Pyruvate is not a commercially important fermentation product.

Fill in the Blank

The microbe responsible for ethanol fermentation for the purpose of producing alcoholic beverages is ________.

Bear witness Answer

The microbe responsible for ethanol fermentation for the purpose of producing alcoholic beverages isyeast (Saccharomyces cerevisiae).

________ results in the production of a mixture of fermentation products, including lactic acid, ethanol and/or acetic acid, and CO_two.

Testify Answer

Heterolactic fermentation results in the production of a mixture of fermentation products, including lactic acid, ethanol and/or acetic acrid, and CO₂.

Fermenting organisms make ATP through the process of ________.

Evidence Answer

Fermenting organisms make ATP through the process of glycolysis.

Matching

Match the fermentation pathway with the right commercial product it is used to produce:

___acetone-butanol-ethanol fermentation	a. breadstuff
___alcohol fermentation	b. pharmaceuticals
___lactic acid fermentation	c. Swiss cheese
___mixed acid fermentation	d. yogurt
___propionic acid fermentation	e. industrial solvents

Call back nearly It

1. Why are some microbes, including Streptococcus spp., unable to perform aerobic respiration, even in the presence of oxygen?
2. How can fermentation be used to differentiate various types of microbes?
3. The bacterium E. coli is capable of performing aerobic respiration, anaerobic respiration, and fermentation. When would it perform each process and why? How is ATP made in each case?

ridgemagain.blogspot.com

Source: https://courses.lumenlearning.com/microbiology/chapter/fermentation/