Entry 17
Probiotic science page
Produces lactic acid to ferment milk and support lactose digestion as a yogurt starter culture.
Overview
Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 is the type strain of this subspecies. Together with Streptococcus thermophilus, it makes up the classic yogurt starter duo [1,2]. The genome of ATCC 11842 was one of the first lactobacillary genomes to be fully sequenced. It revealed extensive ongoing reductive evolution. This is a sign of adaptation from a plant-linked ancestral home to the stable, protein- and lactose-rich milk environment [1]. This strain is mainly studied as a fermented-food starter culture. It is not studied as a targeted therapeutic probiotic. Because of this, strain-specific human RCTs are scarce. The health benefits linked to this organism are mostly documented through yogurt consumption studies [2,3]. L. delbrueckii is the type species of the genus Lactobacillus. It stayed in the narrowed genus after the 2020 reclassification [6].
Mechanism
The genome of ATCC 11842 (1.87 Mb) shows signs of reductive evolution. It has many pseudogenes (broken genes) and incomplete metabolic pathways. This reflects specialization to the dairy environment [1]. It has unusually high rRNA and tRNA gene counts for its genome size. This hints at a recent phase of genome shrinkage [1]. A 47.5-kbp inverted repeat sits in the replication termination region. This is extremely rare in bacterial genomes. It may represent a snapshot of genome evolution in progress [1]. These genome features support the idea that L. bulgaricus adapted to milk by losing unneeded functions. It also developed protocooperation with S. thermophilus. S. thermophilus provides formate and CO₂ that boost L. bulgaricus growth. L. bulgaricus provides amino acids from breaking down proteins [1,2].
At the cell level, freeze resistance of ATCC 11842 depends on membrane properties. These include fatty acid makeup, membrane fluidity, and how the lipid phase changes during cooling [4]. FTIR microspectroscopy shows that freezing changes lipid, protein, and cell wall components. It also increases variation between cells in this freeze-sensitive strain [4].
Health Benefits
Yogurt as a source of health-promoting bacteria (review): L. bulgaricus, as a core yogurt starter, adds to the health benefits of yogurt. These include better lactose digestion and immune system tuning [2]. (Evidence level: review)
Enumeration and quality control (review): Selective counting methods for L. delbrueckii subsp. bulgaricus in yogurt ensure live cells are delivered at useful amounts. This backs up the probiotic claim of fermented dairy products [3]. (Evidence level: review/methodological)
> Note: Strain-specific (ATCC 11842) human RCTs are not available in the literature. Health benefits are documented at the subspecies/yogurt level. This entry cites the organism’s biological characterization and its role in fermented dairy rather than strain-specific therapeutic trials.
Biology
Genome: 1.87 Mb. Shows ongoing reductive evolution with many pseudogenes, high rRNA/tRNA gene density, and a rare 47.5-kbp inverted repeat in the replication termination region [1].
Cryoresistance: Membrane fatty acid makeup and fluidity are key to surviving freezing. ATCC 11842 is fairly freeze-sensitive compared with other lactic acid bacteria [4].
Growth and acid production: ATCC 11842 grows and produces acid in algal carcass fermentation. This shows it can use alternative materials [5].
Protocooperation: Grows together with S. thermophilus in milk. S. thermophilus provides formate and CO₂. L. bulgaricus provides protein breakdown products [1,2].
Taxonomy: L. delbrueckii is the type species of the genus Lactobacillus. It stays in the narrowed genus (sensu stricto) after the 2020 reclassification [6].
Bibliography
[1] van de Guchte M, et al. (2006). “The complete genome sequence of Lactobacillus bulgaricus reveals extensive and ongoing reductive evolution.” Proc Natl Acad Sci U S A. 103(24):9274–9. PMID: 16754859
[2] Kok CR, Hutkins R. (2018). “Yogurt and other fermented foods as sources of health-promoting bacteria.” Nutr Rev. 76(Suppl 1):4–15. PMID: 30452699
[3] Ashraf R, Shah NP. (2011). “Selective and differential enumerations of Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus casei and Bifidobacterium spp. in yoghurt - a review.” Int J Food Microbiol. 149(3):194-208. PMID: 21807435
[4] Girardeau A, et al. (2022). “Insights into lactic acid bacteria cryoresistance using FTIR microspectroscopy.” Anal Bioanal Chem. 414(3):1425–1443. PMID: 34967915
[5] Li C, et al. (2016). “Growth and acid production of Lactobacillus delbrueckii ssp. bulgaricus ATCC 11842 in the fermentation of algal carcass.” J Dairy Sci. 99(6):4243–4250. PMID: 26995135
[6] Zheng J, et al. (2020). “A taxonomic note on the genus Lactobacillus: Description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae.” Int J Syst Evol Microbiol. 70(4):2782–2858. PMID: 32293557
Available Products
ATCC 11842 is available from the American Type Culture Collection as the reference type strain.
L. delbrueckii subsp. bulgaricus is a component of virtually all commercial yogurt starter cultures. It is typically grown together with S. thermophilus.
Many commercial yogurt products contain this subspecies. But specific strain identification beyond subspecies level is rarely shown on consumer packaging.