| Acetobacter aceti | |
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| Species: | A. aceti
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| Acetobacter aceti (Pasteur 1864) Beijerinck 1898
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Acetobacter aceti is a Gram-negative bacterium that moves using its peritrichous flagella. Louis Pasteur proved it to be the cause of conversion of ethanol to acetic acid in 1864. It is a benign microorganism which is present everywhere in the environment, existing in alcoholic ecological niches which include flowers, fruits, honey bees, water and soil.[1] This microbe lives wherever sugar fermentation occurs. It typically grows on substrates rich in sugars, like glucose or other carbon sources. It thrives best in temperatures that range from 25 to 30 degrees Celsius with a max temperature of 35 degrees Celsius and in pH that ranges from 5.5 to 6.3.[1] For a long time it has been used in the fermentation industry to produce acetic acid from alcohol. A. aceti is an obligate aerobe, which means that it requires oxygen to grow as oxygen is used as the terminal electron acceptor.[2]
Acetobacter aceti is economically important because it is used in the production of vinegar by converting the ethanol in wine or cider into acetic acid. The acetic acid created by A. aceti is also used in the manufacturing of acetate rayon, plastics production, rubber production, and photographic chemicals. A. aceti is considered an acidophile, which means it is able to survive in acidic environments, due to having an acidified cytoplasm which makes nearly all proteins in the genome to evolve acid stability. A. aceti has become important in helping to understand the process by which proteins can attain acid stability.
The history of Acetobacter aceti is intertwined with the history of vinegar production and microbial fermentation. The production of vinegar, which come from fermented fruits or grains, dates back thousands of years. Ancient civilization have used vinegar for medicinal and cooking purposes. As time went on, people paid more and more attention to the process of fermentation, which converts sugars into alcohol and then into vinegar in the presence of oxygen. In the late 19th century, Martinus Beijerinck (Dutch microbiologist) isolated various bacteria involved in vinegar production, specifically the genus Acetobacter.[3] In the early 20th century, scientist Louis Pasteur's research identified the role of Acetobacter aceti in the conversion of alcohol to acetic acid. Today, A. aceti is recognized as a species within the genus Acetobacter, belonging to the family Acetobacteraceae in the class Alphaproteobacteria.[4] Research on A. aceti has expanded to explore their biotechnological applications beyond vinegar production including biofuel production, bioremediation, food fermentation, and synthesis of biopolymers.[5]
A. aceti is used for the mass production of acetic acid, the main component in vinegar. During the fermentation process of vinegar production, it is used to act on wines and ciders resulting in vinegar with acetic acid. It can be converted by a silicone tube reactor, which aids the fermentation process with oxidation. A. aceti is widely used in industrial vinegar production due to its ability to produce high concentrations of acetic acid from ethanol while also having a high resistance to acetic acid.[6]
Probiotics have been identified as a method for diabetes treatment. Furthermore, scientists have identified chromium and zinc rich Acetobacter aceti as something that can enhance the hypoglycemic effects of the probiotic. An experiment was conducted in which they compared this Acetobacter aceti to metformin, which is a common treatment for patients with type 2 diabetes. Following the experiment, they were able to conclude that the bacteria, Acetobacter aceti, increased insulin secretion and helped repair damaged pancreatic tissue. [7]
Cellulose is a carbohydrate, specifically a polysaccharide, which can be found in the cell walls of plants, algae, fungi, and some bacteria. Through its production of acetic acid and oxidation of ethanol, A. aceti plays a crucial role in synthesis of bacterial cellulose. Bacterial cellulose is unique from plant cellulose due to its highly pure and crystalline structure. This bacterial cellulose is valued for its high purity, strength, and unique properties. It is used for production of biofilms, medical dressings, and food products.[8][9]
A. aceti is typically known as corrosive as it produces acetic acid which causes severe corrosion of copper and steel in many industrial settings. However, it has also been discovered that when in a solution with ethanol, a biofilm of A. aceti forms and can be used as a protective layer to prevent corrosion of carbon and steel. This is important because if A. aceti biofilms are used to reduce microbiologically induced corrosion, industrial profits will increase.[10]
A. aceti has not been reported as a human pathogen. Human skin does not provide the bacteria with the optimal conditions for it to grow, which makes it safe to handle in factories that use the species to produce acetic acid. However, some evidence indicates it can be harmful to plants and other flora, though it exists naturally in the world.[11]
Oxidation is used to stimulate the growth of the A. aceti. Samples of the bacteria are placed in a few silicone tubes. These tubes are permeable to oxygen, after which they are left in a region warmer than the typical room temperature and cultured. Acetobacter aceti struggles to grow with a carbon source of glucose. However, is grows well on an ethanol medium.[2] Ethanol is a very important compound for the growth of A. aceti. The oxidation of ethanol leads to acetate which lowers the expression of TCA cycle genes. However, this changed once ethanol was added because acetate began to become consumed which led to a unregulation of the glyoxylate pathway upon ethanol oxidation. This means that ethanol is important as a carbon source for the upregulation of metabolic pathways.[12]
A. aceti is a unique microorganism because of its ability to survive in high concentrations of acetic acid. Acetate overoxidation is due to imbalanced metabolic pathways and pumps. A unique feature that this microorganism contains is an efflux pump and the ability for its metabolism to adapt to different environments. The pump serves as a transport mechanism for toxic particles to travel through the cell membrane and cytoplasm, while helping the cell maintain homeostasis. Following, its metabolism can adapt to its surrounding environment and when needed can express genes that aid in acetate metabolism.[6]
As A. aceti accumulates acetate in the presence of ethanol because of incomplete oxidation,[13] catalyzed by the membrane-bound protein pyrroloquinoline quinone-dependent alcohol dehydrogenase (PQQ-dependent ADH), acetate is also used as a carbon and energy source by the tricarboxylic acid (TCA) cycle after ethanol is depleted. Furthermore, the oxidation of ethanol into acetate leads into the creation of adenosine triphosphate (ATP) because of oxidative phosphorylation. Notably, when ethanol is incompletely oxidized by A. aceti, it represses the TCA cycle in A. aceti and it is used as an energy source and the TCA cycle functions to synthesize cell materials.[14]