Microbes can also be differentiated according to the substrates they can ferment. For example, E. The ability to ferment the sugar alcohol sorbitol is used to identify the pathogenic enterohemorrhagic OH7 strain of E. Last, mannitol fermentation differentiates the mannitol-fermenting Staphylococcus aureus from other non—mannitol-fermenting staphylococci.
Identification of a microbial isolate is essential for the proper diagnosis and appropriate treatment of patients. Scientists have developed techniques that identify bacteria according to their biochemical characteristics. Typically, they either examine the use of specific carbon sources as substrates for fermentation or other metabolic reactions, or they identify fermentation products or specific enzymes present in reactions.
In the past, microbiologists have 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. Currently, the various API strips can be used to quickly and easily identify more than species of bacteria, both aerobic and anaerobic, and approximately different types of yeasts.
Based on the colors of the reactions when metabolic end products are present, due to the presence of pH indicators, a metabolic profile is created from the results Figure 2. Figure 2. The API 20NE test strip is used to identify specific strains of gram-negative bacteria outside the Enterobacteriaceae. However, his sluggish reflexes along with his light sensitivity and stiff neck suggest some possible involvement of the central nervous system, perhaps indicating meningitis.
Meningitis is an infection of the cerebrospinal fluid CSF around the brain and spinal cord that causes inflammation of the meninges, the protective layers covering the brain. Meningitis can be caused by viruses, bacteria, or fungi. Although all forms of meningitis are serious, bacterial meningitis is particularly serious. 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 also immediately started him on a course of the antibiotic ceftriaxone, the drug of choice for treatment of meningitis caused by N. Skip to main content. Microbial Metabolism. Search for:. Fermentation Learning Objectives Define fermentation and explain why it does not require oxygen Describe the fermentation pathways and their end products and give examples of microorganisms that use these pathways Compare and contrast fermentation and anaerobic respiration.
Think about It When would a metabolically versatile microbe perform fermentation rather than cellular respiration? Identifying Bacteria by Using API Test Panels Identification of a microbial isolate is essential for the proper diagnosis and appropriate treatment of patients. How might biochemical testing be used to confirm the identity of N.
Fermentation does not involve an electron transport system, and no ATP is made by the fermentation process directly. Microbial fermentation processes have been used for the production of foods and pharmaceuticals, and for the identification of microbes. This discovery paved the way to understand the role of yeast in fermentation.
Figure 2: Louis Pasteur Our modern understanding of the fermentation process comes from the work of the French chemist Louis Pasteur. Life out of nowhere? Nature , Our modern understanding of the fermentation process comes from the work of the French chemist Louis Pasteur Figure 2. Pasteur was the first to demonstrate experimentally that fermented beverages result from the action of living yeast transforming glucose into ethanol.
Moreover, Pasteur demonstrated that only microorganisms are capable of converting sugars into alcohol from grape juice, and that the process occurs in the absence of oxygen.
He concluded that fermentation is a vital process, and he defined it as respiration without air Barnett ; Pasteur Pasteur performed careful experiments and demonstrated that the end products of alcoholic fermentation are more numerous and complex than those initially reported by Lavoisier.
Along with alcohol and carbon dioxide, there were also significant amounts of glycerin, succinic acid, and amylic alcohol some of these molecules were optical isomers — a characteristic of many important molecules required for life. These observations suggested that fermentation was an organic process. To confirm his hypothesis, Pasteur reproduced fermentation under experimental conditions, and his results showed that fermentation and yeast multiplication occur in parallel.
He realized that fermentation is a consequence of the yeast multiplication, and the yeast have to be alive for alcohol to be produced. In , a man named Bigo sought Pasteur's help because he was having problems at his distillery, which produced alcohol from sugar beetroot fermentation. The contents of his fermentation containers were embittered, and instead of alcohol he was obtaining a substance similar to sour milk.
Pasteur analyzed the chemical contents of the sour substance and found that it contained a substantial amount of lactic acid instead of alcohol. When he compared the sediments from different containers under the microscope, he noticed that large amounts of yeast were visible in samples from the containers in which alcoholic fermentation had occurred. In contrast, in the polluted containers, the ones containing lactic acid, he observed "much smaller cells than the yeast.
Alcoholic fermentation occurs by the action of yeast; lactic acid fermentation, by the action of bacteria. By the end of the nineteenth century, Eduard Buchner had shown that fermentation could occur in yeast extracts free of cells, making it possible to study fermentation biochemistry in vitro.
He prepared cell-free extracts by carefully grinding yeast cells with a pestle and mortar. The resulting moist mixture was put through a press to obtain a "juice" to which sugar was added. Using a microscope, Buchner confirmed that there were no living yeast cells in the extract. Upon studying the cell-free extracts, Buchner detected zymase, the active constituent of the extracts that carries out fermentation.
He realized that the chemical reactions responsible for fermentation were occurring inside the yeast. Today researchers know that zymase is a collection of enzymes proteins that promote chemical reactions.
Enzymes are part of the cellular machinery, and all of the chemical reactions that occur inside cells are catalyzed and modulated by enzymes. ATP is a versatile molecule used by enzymes and other proteins in many cellular processes. Glycolysis — the metabolic pathway that converts glucose a type of sugar into pyruvate — is the first major step of fermentation or respiration in cells.
It is an ancient metabolic pathway that probably developed about 3. Because of its importance, glycolysis was the first metabolic pathway resolved by biochemists.
The scientists studying glycolysis faced an enormous challenge as they figured out how many chemical reactions were involved, and the order in which these reactions took place. In glycolysis, a single molecule of glucose with six carbon atoms is transformed into two molecules of pyruvic acid each with three carbon atoms.
In order to understand glycolysis, scientists began by analyzing and purifying the labile component of cell-free extracts, which Buchner called zymase. They also detected a low-molecular-weight, heat-stable molecule, later called cozymase.
Both components were required for fermentation to occur. The complete glycolytic pathway, which involves a sequence of ten chemical reactions, was elucidated around In glycolysis, two molecules of ATP are produced for each broken molecule of glucose. During glycolysis, two reduction-oxidation redox reactions occur. In a redox reaction, one molecule is oxidized by losing electrons, while the other molecule is reduced by gaining those electrons.
A molecule called NADH acts as the electron carrier in glycolysis, and this molecule must be reconstituted to ensure continuity of the glycolysis pathway. Figure 3: Alternative metabolic routes following glycolysis A budding yeast cell is shown with the aerobic and anaerobic metabolic pathways following glycolysis.
The nucleus black and mitochondrion red are also shown. When oxygen is available, pyruvic acid enters a series of chemical reactions known as the tricarboxylic acid cycle and proceeds to the respiratory chain.
As a result of respiration, cells produce 36—38 molecules of ATP for each molecule of glucose oxidized. In the absence of oxygen anoxygenic conditions , pyruvic acid can follow two different routes, depending on the type of cell.
It can be converted into ethanol alcohol and carbon dioxide through the alcoholic fermentation pathway, or it can be converted into lactate through the lactic acid fermentation pathway Figure 3. Since Pasteur's work, several types of microorganisms including yeast and some bacteria have been used to break down pyruvic acid to produce ethanol in beer brewing and wine making.
The other by-product of fermentation, carbon dioxide, is used in bread making and the production of carbonated beverages. Humankind has benefited from fermentation products, but from the yeast's point of view, alcohol and carbon dioxide are just waste products. As yeast continues to grow and metabolize sugar, the accumulation of alcohol becomes toxic and eventually kills the cells Gray This is why the percentage of alcohol in wines and beers is typically in this concentration range. However, like humans, different strains of yeast can tolerate different amounts of alcohol.
Therefore, brewers and wine makers can select different strains of yeast to produce different alcohol contents in their fermented beverages, which range from 5 percent to 21 percent of alcohol by volume. For beverages with higher concentrations of alcohol like liquors , the fermented products must be distilled. Today, beer brewing and wine making are huge, enormously profitable agricultural industries. These industries developed from ancient and empirical knowledge from many different cultures around the world.
Today this ancient knowledge has been combined with basic scientific knowledge and applied toward modern production processes. These industries are the result of the laborious work of hundreds of scientists who were curious about how things work. Barnett, J. A history of research on yeast 1: Work by chemists and biologists, — Yeast 14 , — A history of research on yeast 2: Louis Pasteur and his contemporaries, — Yeast 16 , — A history of research on yeast 3: Emil Fischer, Eduard Buchner and their contemporaries, — Yeast 18 , — Encyclopaedia Britannica's Guide to the Nobel Prizes Godoy, A.
Gray, W. Studies on the alcohol tolerance of yeasts. Journal of Bacteriology 42 , — Huxley, T. Popular Lectures and Addresses II. Chapter IV, Yeast Macmillan, Jacobs, J. Ethanol from sugar: What are the prospects for US sugar crops?
Rural Cooperatives 73 5 Lactic acid fermentation : Lactic acid fermentation is common in muscle cells that have run out of oxygen. The enzyme used in this reaction is lactate dehydrogenase LDH. The reaction can proceed in either direction, but the reaction from left to right is inhibited by acidic conditions.
Such lactic acid accumulation was once believed to cause muscle stiffness, fatigue, and soreness, although more recent research disputes this hypothesis. Once the lactic acid has been removed from the muscle and circulated to the liver, it can be reconverted into pyruvic acid and further catabolized for energy. Another familiar fermentation process is alcohol fermentation, which produces ethanol, an alcohol.
The use of alcohol fermentation can be traced back in history for thousands of years. The chemical reactions of alcoholic fermentation are the following Note: CO 2 does not participate in the second reaction :.
Alcohol Fermentation : Fermentation of grape juice into wine produces CO2 as a byproduct. Fermentation tanks have valves so that the pressure inside the tanks created by the carbon dioxide produced can be released. The first reaction is catalyzed by pyruvate decarboxylase, a cytoplasmic enzyme, with a coenzyme of thiamine pyrophosphate TPP, derived from vitamin B 1 and also called thiamine.
A carboxyl group is removed from pyruvic acid, releasing carbon dioxide as a gas. The loss of carbon dioxide reduces the size of the molecule by one carbon, making acetaldehyde. The fermentation of pyruvic acid by yeast produces the ethanol found in alcoholic beverages. Ethanol tolerance of yeast is variable, ranging from about 5 percent to 21 percent, depending on the yeast strain and environmental conditions. Without these pathways, that step would not occur and no ATP would be harvested from the breakdown of glucose.
Other fermentation methods also occur in bacteria. Many prokaryotes are facultatively anaerobic. This means that they can switch between aerobic respiration and fermentation, depending on the availability of oxygen. Certain prokaryotes, like Clostridia , are obligate anaerobes. Obligate anaerobes live and grow in the absence of molecular oxygen. Oxygen is a poison to these microorganisms, killing them on exposure.
It should be noted that all forms of fermentation, except lactic acid fermentation, produce gas. The production of particular types of gas is used as an indicator of the fermentation of specific carbohydrates, which plays a role in the laboratory identification of the bacteria. Acetogenesis is a biological reaction wherein volatile fatty acids are converted into acetic acid, carbon dioxide, and hydrogen.
Acidogenesis is the second stage in the four stages of anaerobic digestion: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Hydrolysis is a chemical reaction wherein particulates are solubilized and large polymers are converted into simpler monomers.
Acidogenesis is a biological reaction wherein simple monomers are converted into volatile fatty acids. Acetogenes is a biological reaction wherein volatile fatty acids are converted into acetic acid, carbon dioxide, and hydrogen. Finally, methanogenesis is a biological reaction wherein acetates are converted into methane and carbon dioxide, and hydrogen is consumed. Biofuel production can come from plants, algae, and bacteria.
Species of the Clostridium genus allow hydrogen production, a potential biofuel, in mixed cultures. Anaerobic digestion is a complex biochemical process of mediated reactions undertaken by a consortium of microorganisms to convert organic compounds into methane and carbon dioxide. It is a stabilization process, reducing odor, pathogens, and mass reduction. Hydrolytic bacteria form a variety of reduced end-products from the fermentation of a given substrate.
One fundamental question in anaerobic digestion concerns the metabolic features that control carbon and electron flow. This flow is directed toward a reduced end-product during pure culture and mixed methanogenic cultures of hydrolytic bacteria. Thermoanaerobium brockii is a representative thermophilic, hydrolytic bacterium, which ferments glucose, via the Embden—Meyerhof Parnas Pathway. Acidogenic activity was found in the early 20 th century, but it was not until mids that the engineering of phases separation was assumed in order to improve the stability and waste digester treatment.
In this phase, complex molecules carbohydrates, lipids, and proteins are depolymerized into soluble compounds by hydrolytic enzymes cellulases, hemicellulases, amylases, lipases and proteases. The hydrolyzed compounds are fermented into volatile fatty acids acetate, propionate, butyrate, and lactate , neutral compounds ethanol, methanol , ammonia, hydrogen and carbon dioxide. Acetogenesis is one of the main reactions of this stage.
In this reaction, the intermediary metabolites produced are metabolized to acetate, hydrogen, and carbonic gas by the three main groups of bacteria—homoacetogens, syntrophes, and sulphoreductors. For the acetic acid production are considered three kind of bacteria: Clostridium aceticum, Acetobacter woodii , and Clostridium termoautotrophicum. In , Winter and Wolfe demonstrated that A. Fermentation is the process of extracting energy from the oxidation of organic compounds such as carbohydrates.
Pyruvic acid : Pyruvic acid can be made from glucose through glycolysis, converted back to carbohydrates such as glucose via gluconeogenesis, or to fatty acids through acetyl-CoA. It can also be used to construct the amino acid alanine and be converted into ethanol.
0コメント