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''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' (until 2014 known as ''Lactobacillus bulgaricus'') is one of over 200 published species in the ''Lactobacillus'' genome complex (LGC) and is the main
bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
used for the production of
yogurt Yogurt (; , from tr, yoğurt, also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial fermentation of milk. The bacteria used to make yogurt are known as ''yogurt cultures''. Fermentation of sugars in the milk by these bac ...
. It also plays a crucial role in the ripening of some cheeses, as well as in other processes involving naturally
fermented Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
products. It is defined as homofermentive lactic acid bacteria due to
lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as nat ...
being the single end product of its carbohydrate digestion. It is also considered a
probiotic Probiotics are live microorganisms promoted with claims that they provide health benefits when consumed, generally by improving or restoring the gut microbiota. Probiotics are considered generally safe to consume, but may cause bacteria- host ...
. It is a
gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bact ...
rod that may appear long and filamentous. It is non-motile and does not form spores. It is also non-pathogenic. It is regarded as aciduric or acidophilic, since it requires a low pH (around 5.4–4.6) to grow effectively. In addition, it is
anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...
. As it grows on raw dairy products, it creates and maintains the acidic environment that it needs to thrive via its production of lactic acid. In addition, it grows optimally at temperatures of 40–44 °C under anaerobic conditions. It has complex nutritional requirements which vary according to the environment. These include carbohydrates, unsaturated fatty acids, amino acids, and vitamins. First identified in 1905 by the Bulgarian doctor Stamen Grigorov by isolating what later termed ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' from a Bulgarian yogurt sample, the bacteria can be found naturally in the gastrointestinal tract of mammals living in
Shopluk Shopi or Šopi ( South Slavic: Шопи) is a regional term, used by a group of people in the Balkans. The areas traditionally inhabited by the ''Shopi'' or ''Šopi'' is called ''Shopluk'' or ''Šopluk'' (Шоплук), a mesoregion, roughly ...
mesoregion of Balkan peninsula. One strain, ''Lactobacillus bulgaricus'' GLB44, is extracted from the leaves of the ''
Galanthus nivalis ''Galanthus nivalis'', the snowdrop or common snowdrop, is the best-known and most widespread of the 20 species in its genus, ''Galanthus''. Snowdrops are among the first bulbs to bloom in spring and can form impressive carpets of white in areas ...
'' (snowdrop flower) in Bulgaria. The bacterium is also grown artificially in many countries.


Use

''Lactobacillus delbrueckii ''subsp.'' bulgaricus'' is commonly used alongside ''
Streptococcus thermophilus ''Streptococcus thermophilus'' also known as ''Streptococcus salivarius ''subsp.'' thermophilus'' is a gram-positive bacterium, and a fermentative facultative anaerobe, of the '' viridans'' group. It tests negative for cytochrome, oxidase, an ...
'' as a starter for making
yogurt Yogurt (; , from tr, yoğurt, also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial fermentation of milk. The bacteria used to make yogurt are known as ''yogurt cultures''. Fermentation of sugars in the milk by these bac ...
. The ''Lb. bulgaricus'' 2038 strain has been used for decades for yogurt fermentation. The two species work in synergy, with ''L. d. bulgaricus'' producing amino acids from milk proteins, which are then used by ''S. thermophilus''. This relationship is considered to be symbiotic. Both species produce
lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as nat ...
, which gives yogurt its tart flavor and acts as a preservative. The resulting decrease in pH also partially coagulates the milk proteins, such as casein, resulting in yogurt's thickness. While fermenting milk, ''L. d. bulgaricus'' produces acetaldehyde, one of the main yogurt aroma components. Some strains of ''L. d. bulgaricus'', such as ''L. bulgaricus'' GLB44, also produce
bacteriocin Bacteriocins are proteinaceous or peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). They are similar to yeast and paramecium killing factors, and are structurally, functionally, and ec ...
s, which have been shown to kill undesired bacteria ''in vitro''. The viability of ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' is extremely important in that it is necessary for it to be efficient at fermentation and to effectively keep the food products it produces from spoiling. Freeze-drying is the preferred method of preserving the viability of the cells, but not all cells survive this process. Due to its usefulness in natural fermentation processes, specifically in how it makes fermented food products out of cow's milk, it has great economic importance. Some of the biggest importers of the bacterium are Japan, the United States, and the European Union. It has also been considered a contaminant of beer due to its homofermentative production of lactic acid, an off-flavor in many styles of beer. In other styles of beer, however, lactic acid bacteria can contribute to the overall appearance, aroma, taste, and/or mouthfeel, and generally produce an otherwise pleasing sourness.


History

''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' was first identified in 1905 by Stamen Grigorov, who named it ''Bacillus bulgaricus''.
Ilya Metchnikoff Ilya, Iliya, Ilia (name), Ilia, Ilja, or Ilija (russian: Илья́, Il'ja, , or russian: Илия́, Ilija, ; uk, Ілля́, Illia, ; be, Ілья́, Iĺja ) is the East Slavic languages, East Slavic form of the male Hebrew name Eliyahu (Eliah ...
, a professor at the
Pasteur Institute The Pasteur Institute (french: Institut Pasteur) is a French non-profit private foundation dedicated to the study of biology, micro-organisms, diseases, and vaccines. It is named after Louis Pasteur, who invented pasteurization and vaccines ...
in Paris, researched the relationship between the longevity of
Bulgarians Bulgarians ( bg, българи, Bǎlgari, ) are a nation and South Slavic ethnic group native to Bulgaria and the rest of Southeast Europe. Etymology Bulgarians derive their ethnonym from the Bulgars. Their name is not completely unders ...
and their consumption of yogurt. He had the idea that aging is caused by putrefactive activity, or proteolysis, by microbes that produce toxic substances in the intestine. Proteolytic bacteria such as
clostridia The Clostridia are a highly polyphyletic class of Bacillota, including ''Clostridium'' and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them. S ...
, which are part of the normal intestinal flora, produce toxic substances including
phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are ...
,
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
and
indol Indole is an aromatic heterocyclic organic compound with the formula C8 H7 N. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indole is widely distributed in the natural environment ...
s by digestion of
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s. These compounds are responsible for what Metchnikoff called ''intestinal auto-intoxication'', which, according to him, was the cause of the physical changes associated with old age. It was already known at that time that fermentation with
lactic acid bacteria Lactobacillales are an order of gram-positive, low-GC, acid-tolerant, generally nonsporulating, nonrespiring, either rod-shaped ( bacilli) or spherical ( cocci) bacteria that share common metabolic and physiological characteristics. These bact ...
inhibits the deterioration of milk because of its low pH. Metchnikoff's research also noted that rural populations in
Southeastern Europe Southeast Europe or Southeastern Europe (SEE) is a geographical subregion of Europe, consisting primarily of the Balkans. Sovereign states and territories that are included in the region are Albania, Bosnia and Herzegovina, Bulgaria, Croatia (a ...
and the Russian steppes daily consume milk fermented with lactic acid bacteria and live relatively longer than other populations. Based on these data Metchnikoff proposed that consumption of fermented milk seeds the intestine with harmless lactic acid bacteria increasing intestinal acidity and suppressing the growth of proteolytic bacteria. His results were questioned after a 1920 study showed that the bacterium could not survive in the human intestines, but the idea nevertheless started the research into actually useful probiotics. ''Lactobacillus bulgaricus'' is a constituent in VSL#3. This proprietary, standardized, formulation of live bacteria may be used in combination with conventional therapies to treat
ulcerative colitis Ulcerative colitis (UC) is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary symptoms of active disease are abdominal pain and diarrhea mixed with blood (hematochezia). Weight loss, fever, and ...
and requires a prescription. In 2012 it was declared India's national microbe.


Research


Quantification in cow's milk cheese via real-time polymerase chain reaction assay

In 2017, there was a study involving the development of a real-time polymerase chain reaction (
qPCR A real-time polymerase chain reaction (real-time PCR, or qPCR) is a laboratory technique of molecular biology based on the polymerase chain reaction (PCR). It monitors the amplification of a targeted DNA molecule during the PCR (i.e., in real ...
) assay for quantifying ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' as well as ''Streptococcus thermophilus'' in cow's milk cheese. The goal of this study was to create a way to identify and quantify ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' and ''Streptococcus thermophilus,'' two lactic acid producing species crucial to the fermentation and ripening of cheese, in a timely manner through the use of qPCR. Two essays using '' lacZ'' gene targeting PCR primers resulted from this study and were deemed compatible with the two lactic acid bacteria ( LAB) species. This allowed for the direct quantification of ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' and ''Streptococcus thermophilus'' in cheese produced from unpasteurized cow's milk.


Effects of ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' on antigenicity of milk proteins

A study in 2012 posed the question of whether or not ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' had any effect on the antigenicity of four kinds of milk proteins, being α-lactalbumin (α-LA),
β-lactoglobulin β-Lactoglobulin (BLG) is the major whey protein of cow and sheep's milk (~3 g/L), and is also present in many other mammalian species; a notable exception being humans. Its structure, properties and biological role have been reviewed many times. ...
(β-LG), α-casein (α-CN), and β-casein (β-CN). These proteins are the main proteins found in cow's milk and are known to have
antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune respons ...
ic properties in humans, especially young children and infants. 2–5% of young children and infants experience cow's milk protein allergy (CMPA), which has harmful effects on their development and may even result in death. This allergy is facilitated through the antigenicity of the milk proteins, which is the ability of the proteins to trigger an immune response in the body that can result in a number of possible allergic reactions. The study was performed by simulating digestion of unfermented milk and milk that was fermented through exposure to ''Lactobacillus delbrueckii subsp. bulgaricus'' to compare their antigenicities in order to see if fermentation had any effect on the antigenicity of the proteins. The antigenicities were measured through an
enzyme-linked immunosorbent assay The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay uses a solid-phase type of enzyme immunoassay (EIA) to detect the presence ...
(ELISA). The results claimed that the fermentation of cow's milk by ''Lactobacillus delbrueckii subsp. bulgaricus'' reduced the antigenicity of α-LA and β-CN. However, it also increased the antigenicity of α-CN while β-LG was not impacted.


Subcellular membrane fluidity of ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' under cold and osmotic stress

The efficiency of lactic acid bacteria
cryopreservation Cryo-preservation or cryo-conservation is a process where organisms, organelles, cells, tissues, extracellular matrix, organs, or any other biological constructs susceptible to damage caused by unregulated chemical kinetics are preserved by co ...
is not consistent and may lead to cell death. ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' has adapted to defend against cold stress. The way most cells react to the cold is by changing the fluidity of the cellular membrane, but this particular bacterium has acquired different tactics to fight against cold stress. The first way to cope with the cold is to increase viscosity by taking in compounds such as
disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three common examples are sucrose, la ...
s, polysaccharides,
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s and antioxidants. The second strategy used is performed by inducing active responses during the fermentation or post-fermentation processes. By modifying these it will change the temperature, pH and medium composition. This results in specific metabolic pathways becoming active, with the synthesis of cold shock proteins.


Effects of sorbitol, NaCl, and sodium glutamate on the survivability of ''Lactobacillus delbruekii'' subsp. ''bulgaricus'' during freeze-drying processes

In 2017, a study was done to see the effects of six different substances on the growth and freeze- drying of
Lactobacillus ''Lactobacillus'' is a genus of Gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria. Until 2020, the genus ''Lactobacillus'' comprised over 260 phylogenetically, ecologically, and metabolically div ...
. Using Lactobacillus as starter cultures for the dairy industry depends on the number of viable and active cells. Currently, the preferred method to preserve the bacterial cells is through freeze-drying, however this also results in some strains being killed. This is due to various complications of freeze-drying, including the formation of ice crystals, loss of membrane fluidity, and the denaturation of important macromolecules. Regardless, freeze-drying has been used for decades in microbiological research as a way to store and stabilize cultures. Six substances, being NaCl, sorbitol, mannitol, mannose, sodium glutamate, and betaine were tested to determine if they had any effect on the survivability of the cells after freeze-drying. Three of the six substances added had a positive effect on the growth and freeze-drying of Lactobacillus, being NaCl, sorbitol, and sodium glutamate. The results suggest that these substances have protective effects on ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' in small concentrations, but have little effect or even some harmful effects in higher concentrations. The optimal concentrations for sorbitol, NaCl and sodium glutamate for the desired protective effects were 0.15%, 0.6%, and 0.09% respectively. This was shown to increase cell viability drastically.


Immunotherapy for cancer

According to Helen Nauts from Cancer Research Institute, on a monograph reviewing the effects of bacterial infections on multiple types of cancer, Ivan Bogdanov, a Bulgarian physician, allegedly produced a vaccine consisting of lactobacillus bulgaricus and used it to treat two patients with myeloma, inducing remission in the two cases, one dying 18 months later due to influenza, and another living 45 months (survival median at the time was about 12–18 months). However, references are internal documents and conversations among hospitals; there's no mention in English medical literature. An article from a commercial site and an alleged documentary are available (in Bulgarian).


References


Bibliography

* *


External links

*
Type strain of ''Lactobacillus delbrueckii subsp. bulgaricus'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
* {{DEFAULTSORT:Lactobacillus Delbrueckii Subsp. Bulgaricus Lactobacillaceae Bacteria used in dairy products Probiotics Bacteria described in 1919 Subspecies