The MicroByte Series: Bacillus bulgaricus- The First Probiotic

BugSpeaks

May 21, 2025

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4 min read

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MicroByte Series

History

The Bulgarian traditional practice of making yoghurt involved storing milk in a lamb's skin bag, wrapped around the waist. In 1905, this mystery captured the attention of Dr Stamen Grigorov, a Bulgarian microbiologist. He wondered what was responsible for the milk becoming yoghurt. Grigorov’s extensive research identified that the specific rod-shaped bacteria were responsible for yoghurt production. Since this bacterium was first found in Bulgaria, it was named Bacillus bulgari.

At the same time, Dr. Élie Metchnikoff also noticed a fascinating anomaly in this South European country. Within a population of 3,000,000, over 3,000 centenarians were actively performing daily activities that people aged 65 in other parts of the world typically could not manage. Metchnikoff directly associated this lifestyle with Bulgaria's most traditional food, the Bulgarian Yoghurt.

He also strongly believed that the toxin-producing harmful bacteria in the large intestine were responsible for ill health and accelerated the aging process. At that time, Metchnikoff was aware that the milk fermented with bacteria like Bacillus bulgari would inhibit the usual bacteria responsible for the spoilage of milk, because of their ability to ferment milk sugar, lactose, to lactic acid. Based on these observations and evidence, he asserted that daily consumption of fermented milk products would “seed” the beneficial lactic acid bacteria, favouring the suppression of harmful toxin-producing bacteria, therefore prolonging the life of Bulgarians. Whether or not lactic acid bacteria were the sole reason for the longevity of Bulgarians, the discovery of Bacillus bulgari by Dr Stamen Grigorov, along with Dr. Élie Metchnikoff’s observation, was an important milestone in the history of modern probiotics research and human health.

Metchnikoff’s theory on the intake of fermented milk products, did “seed” an idea in the minds of the researchers. Even a century after his observation, numerous studies continue to be published in support of the beneficial effect of fermented milk products with lactic acid bacteria. Bacillus bulgari, now called Lactobacillus delbrucki sub sp bulgari, is widely used for its several advantageous properties.

Toxin-producing- Capable of generating poisonous substances (toxins) that can cause cellular damage, inflammation, or illness inside a host body.

Large intestine- The final major section of the digestive tract (the colon) is responsible for absorbing remaining water, processing waste, and housing billions of beneficial gut microbes.

Fermented- Chemically broken down by helpful bacteria, yeasts, or other microbes, usually converting raw sugars into beneficial acids, gases, or alcohol.

Lactose- A natural, unique sugar found exclusively in milk and dairy products that requires specific digestive enzymes to break down properly.

Lactic acid- A mild, organic acid produced by friendly bacteria during fermentation that gives sour foods their pleasant tang and naturally preserves them by keeping harmful germs away.

Health Benefits

Lactobacillus delbrucki sub sp bulgari probiotic supplementation has demonstrated numerous health benefits. A study revealed that oral supplementation ofLactobacillus delbrucki sub sp bulgariin an elderly population enhanced immunity by increasing the production of anti-microbial proteins and immune cells, thus conferring better resistance to infections and improving immune response to vaccines. In another study, daily consumption of the probiotic Lactobacillus delbrucki sub sp bulgari, has shown its potential to reduce blood triglyceride levels, thereby aiding in the prevention of metabolic syndrome. Additionally, it exhibited anti-inflammatory properties and has been associated with reducing the severity of acne.

Probiotic supplementation- The dietary habit of regularly consuming capsules, powders, or enriched foods packed with live, beneficial bacteria to actively improve gut health.

Anti-microbial proteins- Small, natural proteins manufactured by the body or friendly microbes that function as built-in weapons to directly damage or kill invading germs.

Immune cells- Specialised defensive white blood cells that constantly patrol tissues to detect, track down, and destroy foreign invaders like dangerous bacteria and viruses.

Vaccines- Safe biological mixtures that proactively train the body's immune system to recognise, remember, and destroy specific dangerous germs before a real infection can strike.

Blood triglyceride levels- A clinical measurement of the most common type of fat circulating in your bloodstream, which the body uses for energy or stores as fat tissue.

Metabolic syndrome: A dangerous cluster of co-occurring conditions, including high blood pressure, elevated blood sugar, excess abdominal fat, and abnormal cholesterol that spikes the risk of heart disease and stroke.

Anti-inflammatory properties- The natural ability of a specific food, compound, or medicine to actively soothe and reduce swelling, heat, and irritation inside body tissues.

Industrial Applications

Lactobacillus delbrueckii sub sp bulgari has gained significant popularity for its ability to break down milk sugar-lactose into lactic acid, a quality appreciated by the food industry. The lactic acid produced through the fermentation process increases the acidity of the milk, which leads to the coagulation of milk proteins like casein, which converts liquid milk to a semi-solid, gel-like form, the renowned yoghurt. Apart from yoghurt production, it contributes to the desired flavour and tartness of a variety of cheeses and is also used in the production of traditional fermented drinks like kumiss. In addition, the lactic acid is used in the acidification of jams, jellies, and soft drinks, thereby acting as a natural preservative and extending the shelf life of consumables.

Casein- The primary slow-digesting protein family found in milk, clumps together during fermentation to give foods like yogurt and cheese their thick, solid texture.

Tartness- A sharp, pleasantly sour, or tangy taste sensation usually triggered by the presence of natural organic acids in fermented foods or citrus fruits.

Kumiss- A historic, slightly sparkling fermented dairy beverage traditionally crafted from raw mare's milk, deeply rooted in the food culture of Central Asian communities.

Fun facts

Ever wondered where yoghurt bacteria came from?

Traditionally, one of the ways Bulgarian yoghurt was prepared was by placing the branch of a native plant into sheep’s milk, which was boiled and cooled. This has raised a question about the origin of yoghurt bacteria- does it come from plants? A study was conducted in 2007 (almost exactly a century after Dr Grigorov’s initial experiments!) by fermenting milk with plant branches and comparing it with commercially available Bulgarian yoghurt. Surprisingly, there was no difference between the texture and flavour of the two yoghurts.

The bacteria isolated from the plants were the same as those used for yoghurt preparation, Lactobacillus delbruckii subsp. bulgaricus and Streptococcus thermophilus.This suggests that the yoghurt bacteria may indeed have originally come from plants!

Microbes Profile

Shape: Rod

Gram nature: Gram-positive

Spore formation: No

Biofilm formation: Yes

Oxygen requirement: Aerotolerant-can tolerate oxygen and can grow in the absence of oxygen

Optimal temperature: 43-46°C

Optimal pH: 5.8 to 6

Food source: Lactose and Glucose

Taxonomic Classification

Domain: Bacteria

Phylum: Bacillota

Class: Bacilli

Order: Lactobacillales

Family: Lactobacillaceae

Genus: Lactobacillus

Species: Lactobacillus delbrueckii

Subspecies: Lactobacillus delbrueckii subsp. Bulgaricus

-Khushi C

Reference

Chu, P. Y., Yu, Y. C., Pan, Y. C., Dai, Y. H., Yang, J. C., Huang, K. C., & Wu, Y. C. (2024). The Efficacy of Lactobacillus delbrueckii ssp. bulgaricus Supplementation in Managing Body Weight and Blood Lipids of People with Overweight: A Randomized Pilot Trial. Metabolites, 14(2), 129. https://doi.org/10.3390/metabo14020129.

Moro-García, M. A., Alonso-Arias, R., Baltadjieva, M., Fernández Benítez, C., Fernández Barrial, M. A., Díaz Ruisánchez, E., Alonso Santos, R., Alvarez Sánchez, M., Saavedra Miján, J., & López-Larrea, C. (2013). Oral supplementation with Lactobacillus delbrueckii subsp. bulgaricus 8481 enhances systemic immunity in elderly subjects. Age (Dordrecht, Netherlands), 35(4), 1311–1326. https://doi.org/10.1007/s11357-012-9434-6

Kim, J., Ko, Y., Park, Y. K., Kim, N. I., Ha, W. K., & Cho, Y. (2010). Dietary effect of lactoferrin-enriched fermented milk on skin surface lipid and clinical improvement of acne vulgaris. Nutrition (Burbank, Los Angeles County, Calif.), 26(9), 902–909. https://doi.org/10.1016/j.nut.2010.05.011

Jung, G. W., Tse, J. E., Guiha, I., & Rao, J. (2013). Prospective, randomized, open-label trial comparing the safety, efficacy, and tolerability of an acne treatment regimen with and without a probiotic supplement and minocycline in subjects with mild to moderate acne. Journal of cutaneous medicine and surgery, 17(2), 114–122. https://doi.org/10.2310/7750.2012.12026

Michaylova, M., Minkova, S., Kimura, K., Sasaki, T., & Isawa, K. (2007). Isolation and characterization of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus from plants in Bulgaria. FEMS microbiology letters, 269(1), 160–169. https://doi.org/10.1111/j.1574-6968.2007.00631.x

Frazier, W.C. and Westhoff, D.C. (2017) Food Microbiology. 5th Edition, Tata McGraw Hill, Inc., New York.

BACILLUS BULGARICUS

PROBIOTICS

Frequently Asked Questions

How did Dr. Stamen Grigorov originally discover the secret behind traditional Bulgarian yogurt?

In 1905, the Bulgarian microbiologist investigated the mystery of milk turning into yogurt within traditional lamb's skin bags. His extensive research successfully isolated the specific rod-shaped bacterium responsible, which was initially named Bacillus bulgari.

What was Dr. Élie Metchnikoff’s historic theory regarding yogurt and human longevity?

He believed that toxin-producing harmful bacteria in the large intestine accelerated aging and caused poor health. He asserted that daily Bulgarian yogurt consumption seeded beneficial lactic acid bacteria to actively suppress these dangerous toxins.

What specific immune and metabolic health benefits does this probiotic strain provide?

Oral supplementation enhances elderly immunity by increasing antimicrobial proteins and improving vaccine responses against dangerous infections. Additionally, daily consumption can lower blood triglyceride levels to aid in preventing metabolic syndrome.

How does the bacterium physically transform liquid milk into a thick, semi-solid yogurt?

The bacterium effectively ferments milk sugar, lactose, into lactic acid, which rapidly raises the overall acidity. This biochemical shift causes milk proteins like casein to coagulate, turning the liquid into a thick, semi-solid gel.

What did a scientific study reveal about the surprising environmental origin of yogurt bacteria?

A 2007 study proved that milk fermented with native plant branches produced identical texture and flavor to commercial Bulgarian yogurt. Researchers successfully isolated the exact same bacterial strains from the plants, suggesting they originally came from flora.

BugSpeaks®

BugSpeaks®, developed by Leucine Rich Bio Pvt Ltd, South Asia’s first microbiome company, is headquartered in Bengaluru, India. Since 2014, the company has pioneered advanced analytics to analyze complex genomics data. Collaborating with leading research institutes globally, Leucine Rich Bio has leveraged its expertise to create BugSpeaks®, South Asia’s first gut microbiome test.

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