bulgaricus

Lactobacillus delbrueckii subsp. bulgaricus, commonly referred to as L. bulgaricus, is a Gram-positive, rod-shaped lactic acid bacterium used in dairy fermentation, most notably in yogurt production. It is thermophilic, growing best at elevated temperatures around 40 to 45°C, and it tolerates increasingly acidic environments as fermentation proceeds. Its primary metabolic activity is the fermentation of lactose to lactic acid, which contributes to the texture and tang of fermented dairy products.

Taxonomy and naming details trace back to the early 20th century. The organism was originally described as Lactobacillus bulgaricus and was named after Bulgaria, where Stamen Grigorov isolated it in 1905 from traditional yogurt. In later taxonomic revisions it was reclassified as Lactobacillus delbrueckii subsp. bulgaricus, reflecting its close relationship to other L. delbrueckii strains.

Role in yogurt production is defined by a mutualistic relationship with Streptococcus thermophilus. In starter cultures, the two bacteria cooperate to ferment milk: S. thermophilus rapidly acidifies the milk and liberates peptides and amino acids that stimulate L. bulgaricus growth, while L. bulgaricus proteolysis releases peptides and amino acids that sustain S. thermophilus. This interaction enhances the development of flavor, aroma, and texture, and helps achieve the characteristic final acidity of yogurt.

Characteristics and growth conditions include its thermophilic nature, preference for high-temperature fermentation, and tolerance of acidic environments. It is typically used in dairy manufacturing as part of a starter culture alongside S. thermophilus, and is also studied for its contributions to flavor compounds and potential probiotic properties in some strains.

In summary, bulgaricus is a key thermophilic lactic acid bacterium essential to traditional yogurt fermentation and related dairy products.