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 used for the production of yogurt. It also plays a crucial role in the ripening of some cheeses, as well as in other processes involving naturally fermented products.
It is defined as homofermentive lactic acid bacteria due to the way it feeds on the milk sugar lactose to produce lactic acid, which helps preserve milk. It is also considered a probiotic.
Use in industry
It is a gram-positive 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.
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 Lactobacillus bulgaricus by the Bulgarian doctor Stamen Grigorov by isolating it from a yogurt sample, Lactobacillus delbrueckii subsp. bulgaricus can be found naturally in the gastrointestinal tract of mammals living in Bulgaria.
One strain, Lactobacillus bulgaricus GLB44, is extracted from the leaves of the Galanthus nivalis (snowdrop flower) in Bulgaria as well. The bacterium is also grown artificially in many countries. It is the national microorganism of India.
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 in Paris, researched the relationship between the longevity of Bulgarians 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, which are part of the normal intestinal flora, produce toxic substances including phenols, ammonia and indols by digestion of proteins. 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, a concept that has no scientific basis. It was already known at that time that fermentation with lactic acid bacteria inhibits the deterioration of milk because of its low pH.
Metchnikoff’s research also noted that rural populations in Southeastern Europe 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.
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 and requires a prescription.
In 2012 it was declared India’s national microbe.
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 bulgaricus 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 assays 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 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 antigenic 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 the 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 (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 bulgaricus delbrueckii subsp. bulgaricus under cold and osmotic stress
The efficiency of lactic acid bacteria cryopreservation 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 disaccharides, polysaccharides, amino acids 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. Using Lactobacillus bulgaricus 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 bulgaricus 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 .15%, .6%, and .09% respectively. This was shown to increase cell viability drastically.
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- Wittouck, Stijn; Wuyts, Sander; Meehan, Conor J.; van Noort, Vera; Lebeer, Sarah (2019-09-03). Gibbons, Sean M. (ed.). “A Genome-Based Species Taxonomy of the Lactobacillus Genus Complex”. mSystems. 4 (5): e00264–19, /msystems/4/5/msys.00264–19.atom. doi:10.1128/mSystems.00264-19. ISSN 2379-5077. PMC 6722421. PMID 31481601.
- Stachelska, Milena Alicja; Foligni, Roberta (2018). “Development of a time-effective and highly specific quantitative real-time polymerase chain reaction assay for the identification of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in artisanal raw cow’s milk cheese”. Acta Veterinaria Brno. 87 (3): 301–308. doi:10.2754/avb201887030301. ISSN 0001-7213.
- “Lactobacillus delbrueckii – microbewiki”. microbewiki.kenyon.edu. Retrieved 2019-11-14.
- School of Food and Biological Engineering, Shaanxi University of Science and Technology Xi?an,China; Shaanxi Heshi Dairy, China; Chen, He; Huang, Jie; Shi, Xiaoyu; Li, Yichao; Liu, Yu (2017-12-30). “Effects of six substances on the growth and freeze-drying of Lactobacillus delbrueckii subsp. bulgaricus [pdf]”. Acta Scientiarum Polonorum Technologia Alimentaria. 16 (4): 403–412. doi:10.17306/J.AFS.2017.0512.
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The Minister also announced the National Microbe for India which was selected by children who had visited the Science Express Biodiversity Special, a train which has been visiting various stations across the country. Voting for the National Microbe took place in these stations and the children have selected the Lactobacillus (Lactobacillus delbrueckii subsp. bulgaricus) to be the National Microbe for India
- Zheng, Zhe; Liao, Ping; Luo, Yongkang; Li, Zheng (June 2014). “Effects of Fermentation by Lactobacillus delbrueckii subsp. bulgaricus , Refrigeration and Simulated Gastrointestinal Digestion on the Antigenicity of Four Milk Proteins: Effects on Milk Protein Antigenicity”. Journal of Food Processing and Preservation. 38 (3): 1106–1112. doi:10.1111/jfpp.12069.
- Meneghel, Julie; Passot, Stéphanie; Cenard, Stéphanie; Réfrégiers, Matthieu; Jamme, Frédéric; Fonseca, Fernanda (September 2017). “Subcellular membrane fluidity of Lactobacillus delbrueckii subsp. bulgaricus under cold and osmotic stress”. Applied Microbiology and Biotechnology. 101 (18): 6907–6917. doi:10.1007/s00253-017-8444-9. ISSN 0175-7598. PMID 28780605.
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