Lactobacillus Bulgaricus
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''Lactobacillus bulgaricus'' is the main
bacterium Bacteria (; : 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 among the ...
used for the production of
yogurt Yogurt (; , from , ; also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial Fermentation (food), fermentation of milk. Fermentation of sugars in the milk by these bacteria produces lactic acid, which acts on milk protein to ...
. It also plays a crucial role in the ripening of some
cheese Cheese is a type of dairy product produced in a range of flavors, textures, and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk (usually the milk of cows, buffalo, goats or sheep). During prod ...
s, as well as in other processes involving naturally
fermented Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic compound, Organic molecules, such as glucose or other sugars, are Catabo ...
products. It is defined as homofermentive lactic acid bacteria due to
lactic acid Lactic acid is an organic acid. It has the molecular formula C3H6O3. 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 wel ...
being the single end product of its carbohydrate digestion. It is also considered a
probiotic Probiotics are live microorganisms that provide health benefits when consumed, generally by improving or restoring the microbiota in the gut. Probiotics are considered generally safe to consume, but may cause bacteria– host interactions ...
. 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. The Gram stain is ...
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 Acidophiles or acidophilic organisms are those that thrive under highly acidic conditions (usually at pH 5.0 or below). These organisms can be found in different branches of the tree of life, including Archaea, Bacteria,Becker, A.Types of Bacteri ...
, 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: *Adhesive#Anaerobic, Anaerobic ad ...
. 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 Bulgaricus'' from a Bulgarian yogurt sample, the bacteria can be found naturally in the gastrointestinal tract of mammals living in Sofia region and along the Balkan Mountain (Stara Planina) 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'' formerly known as ''Streptococcus salivarius ''subsp.'' thermophilus'' is a gram-positive bacteria, gram-positive bacterium, and a lactic acid fermentation, fermentative facultative anaerobic organism, facultative ...
'' as a starter for making
yogurt Yogurt (; , from , ; also spelled yoghurt, yogourt or yoghourt) is a food produced by bacterial Fermentation (food), fermentation of milk. Fermentation of sugars in the milk by these bacteria produces lactic acid, which acts on milk protein to ...
. 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 the molecular formula C3H6O3. 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 wel ...
, 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 Acetaldehyde (IUPAC systematic name ethanal) is an organic compound, organic chemical compound with the chemical formula, formula , sometimes abbreviated as . It is a colorless liquid or gas, boiling near room temperature. It is one of the most ...
, 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 peptide, 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 ...
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, a professor at the
Pasteur Institute The Pasteur Institute (, ) 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 for anthrax and rabies. Th ...
in Paris, researched the relationship between the longevity of
Bulgarians Bulgarians (, ) are a nation and South Slavs, South Slavic ethnic group native to Bulgaria and its neighbouring region, who share a common Bulgarian ancestry, culture, history and language. They form the majority of the population in Bulgaria, ...
and their consumption of yogurt. He had the idea that aging is caused by putrefactive activity, or
proteolysis Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Protein degradation is a major regulatory mechanism of gene expression and contributes substantially to shaping mammalian proteomes. Uncatalysed, the hydrolysis o ...
, 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 ...
, 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 ar ...
,
ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
and indols by digestion of
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
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 is a geographical sub-region of Europe, consisting primarily of the region of the Balkans, as well as adjacent regions and Archipelago, archipelagos. There are overlapping and conflicting definitions of t ...
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. In 2012 it was declared India's national microbe.


Taxonomic history

In bacterial taxonomy, the
basionym In the scientific name of organisms, basionym or basyonym means the original name on which a new name is based; the author citation of the new name should include the authors of the basionym in parentheses. The term "basionym" is used in both botan ...
for ''L. d. bulgaricus'' was "Thermobacterium bulgaricum" . The entity became ''Lactobacillus bulgaricus'' in 1973 with the work of Rugosa and Hansen, and was reclassified as a subspecies under ''Lactobacillus delbrueckii'' in 1984.


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) 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 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-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, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...
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 is a solid-phase type of enzyme immunoassay (EIA) to detect the presence o ...
(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 under cold and osmotic stress

The efficiency of lactic acid bacteria
cryopreservation Cryopreservation or cryoconservation is a process where biological material - cells, tissues, or organs - are frozen to preserve the material for an extended period of time. At low temperatures (typically or using liquid nitrogen) any cell ...
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, ...
s,
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...
s,
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
s and
antioxidant Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...
s. 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.


Survival 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 In biology, membrane fluidity refers to the viscosity of the lipid bilayer of a cell membrane or a synthetic lipid membrane. Lipid packing can influence the fluidity of the membrane. Viscosity of the membrane can affect the rotation and diffusion ...
, and the denaturation of important
macromolecules A macromolecule is a "molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass." Polymers are physi ...
. Regardless, freeze-drying has been used for decades in microbiological research as a way to store and stabilize cultures. Six substances, being
sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...
,
sorbitol Sorbitol (), less commonly known as glucitol (), is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alco ...
,
mannitol Mannitol is a type of sugar alcohol used as a sweetener and medication. It is used as a low calorie sweetener as it is poorly absorbed by the intestines. As a medication, it is used to decrease pressure in the eyes, as in glaucoma, and to l ...
,
mannose Mannose is a sugar with the formula , which sometimes is abbreviated Man. It is one of the monomers of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylatio ...
,
monosodium glutamate Monosodium glutamate (MSG), also known as sodium glutamate, is a sodium salt of glutamic acid. MSG is found naturally in some foods including tomatoes and cheese in this glutamic acid form. MSG is used in cooking as a flavor enhancer with a ...
, and
betaine A betaine () in chemistry is any neutral chemical compound with a positively charged cationic functional group that bears no hydrogen atom, such as a Quaternary ammonium cation, quaternary ammonium or phosphonium cation (generally: Onium compou ...
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 sodium chloride, 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, sodium chloride 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