The Discovery: A Bulgarian's Contribution
The story of Lactobacillus bulgaricus begins in 1905, in a laboratory at the University of Geneva. A young Bulgarian medical student and microbiologist, Stamen Grigorov, was conducting research on the traditional fermented milk product from his home country, known as kiselo mlyako. Using a microscope, he identified the specific rod-shaped microorganism responsible for the unique fermentation process.
Recognizing the significance of the discovery, Grigorov named the bacterium after his home country, Bulgaria, calling it Bacillus bulgaricus. His finding was published and later championed by Russian Nobel laureate Ilya Metchnikoff, who theorized that the longevity of Bulgarian peasants was linked to their high consumption of yogurt containing this bacillus. This endorsement helped popularize both the yogurt and the bacterium internationally, solidifying the name's place in history.
From Bacillus to Subspecies: The Taxonomy of bulgaricus
While the original name was Bacillus bulgaricus, the scientific community later reclassified the organism. In 1984, the bacterium was designated a subspecies under a different species, receiving its modern, more specific name: Lactobacillus delbrueckii subsp. bulgaricus. Despite this technical change, the common name 'bulgaricus' remains a testament to its origin and initial discovery.
Beyond the Name: The Role in Traditional Yogurt
L. bulgaricus is a homofermentative lactic acid bacterium, meaning it primarily produces lactic acid during fermentation. However, it is not the sole actor in traditional yogurt production. It works symbiotically with another bacterium, Streptococcus thermophilus, to create the signature flavor and texture of yogurt.
- Streptococcus thermophilus: This bacterium grows faster initially, producing lactic acid that lowers the pH of the milk. This creates a favorable, acidic environment for L. bulgaricus to thrive.
- Lactobacillus bulgaricus: This microbe continues to produce lactic acid, significantly contributing to the final acidity and tanginess of the yogurt. It also produces acetaldehyde, which is responsible for the characteristic fresh, aromatic flavor.
Comparison: L. bulgaricus vs. S. thermophilus
| Feature | Lactobacillus bulgaricus | Streptococcus thermophilus |
|---|---|---|
| Classification | Rod-shaped bacterium | Sphere-shaped bacterium (coccus) |
| Primary Role | Flavor and acidity | Initial lactic acid production |
| Byproduct | Lactic acid & acetaldehyde | Lactic acid |
| pH Range | Prefers lower pH (acidic) | Initiates growth at higher pH |
| Growth Temperature | Optimal at 40–44 °C | Often grows symbiotically with L. bulgaricus |
| Longevity | Contributes to post-acidification in storage | Declines more quickly in acidic environment |
Cultural Significance and Global Spread
Bulgarian yogurt is more than just a food item; it is a point of national pride. Passed down through generations, the traditional methods of making kiselo mlyako have preserved the integrity of the unique bacterial cultures. The village of Studen Izvor, Grigorov's birthplace, even houses the world's only yogurt museum, celebrating this cultural heritage.
Following Metchnikoff's research and the subsequent international attention, the reputation of Bulgarian yogurt and its health benefits spread. In the 1970s, the Japanese company Meiji acquired the rights to the Bulgarian culture, launching its own highly successful yogurt product that remains popular today. The global demand for probiotics has kept L. bulgaricus relevant, driving scientific research into its properties and applications far beyond traditional dairy.
The Broader Impact: From Health Claims to Modern Science
Early health claims for L. bulgaricus suggested it modified intestinal flora, potentially limiting auto-intoxication and promoting longevity. While later studies questioned the ability of this specific bacterium to survive and colonize the human gut permanently, Metchnikoff's theories nevertheless laid the groundwork for modern probiotic research.
Today, L. bulgaricus is a safe and well-understood probiotic, with recognized benefits, including the alleviation of lactose intolerance and potential immunomodulatory effects. For example, certain strains have been shown to enhance immunity in elderly populations. Research continues on optimizing starter cultures for different applications, including plant-based yogurts and other fermented products. Furthermore, scientists have isolated new strains from diverse sources within Bulgaria, highlighting the country's ongoing importance as a genetic reservoir for beneficial lactic acid bacteria.
Conclusion: A Name That Honors a Nation's Heritage
The reason it is called bulgaricus is a direct nod to the country of Bulgaria and the pioneering work of its native son, Stamen Grigorov. More than a simple geographical descriptor, the name carries with it the rich history of a national dairy tradition, the legacy of a scientific discovery that sparked the probiotic movement, and a centuries-old cultural pride. Though its taxonomy has been refined over the years, the essence of the name remains—a lasting tribute to the place where its story began.
Read more about the scientific research into Lactobacillus delbrueckii subsp. bulgaricus and its probiotic characteristics here: Probiotic Characteristics and Health Benefits of the Yogurt Starter Bacteria Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus.
