A defined thermophilic dairy fermentation community composed of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. The two lactic-acid bacteria form the canonical yogurt starter association, where metabolite exchange accelerates milk acidification: S. thermophilus provides formate, carbon dioxide, and urease-dependent ammonia/carbon dioxide effects that stimulate the lactobacillus, while proteolytic activity of L. delbrueckii subsp. bulgaricus releases peptides and amino acids that support the more weakly proteolytic streptococcus.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Streptococcus thermophilus | NCBITaxon:1308 · TaxonMech · TraitMech |
CROSS_FEEDER
SECONDARY_FERMENTER
|
N/A |
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| Lactobacillus delbrueckii subsp. bulgaricus | NCBITaxon:1585 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
CROSS_FEEDER
|
N/A |
|
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Ecological Interactions
The graph shows only explicitly linked interaction participants. Community members without an asserted participant link are omitted; membership alone does not imply an interaction.
Streptococcus Formate and Carbon Dioxide Support
CROSS_FEEDINGPARTIAL mechanistic model: supplementation and transcriptome responses in S. thermophilus CNRZ1066 with L. bulgaricus ATCC BAA-365 support formate-related nutritional assistance. Carbon-dioxide provision is inferred rather than a quantified transfer in that study; urease experiments distinguish CO2-responsive from unresponsive lactobacillus strains. This species-level record combines exact strain-pair studies, not one universally beneficial pair.
Source Taxon: Streptococcus thermophilus
Target Taxon: Lactobacillus delbrueckii subsp. bulgaricus
Metabolites: formate (CHEBI:15740 · MediaIngredientMech · CMMMech), carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech)
Biological Processes:
- fermentation (GO:0006113 · PathwayMech)
- interspecies interaction between organisms (GO:0044419 · PathwayMech)
Evidence
-
PMID:20889781 - PARTIAL (IN_VITRO)"formic acid, folic acid, and fatty acids are provided by S. thermophilus"
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PMID:20889781 - PARTIAL (IN_VITRO)"folic acid and carbon dioxide"
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PMID:24936380 - PARTIAL (IN_VITRO)"earlier l-lactate and formate accumulation"
Lactobacillus Proteolytic Nitrogen Support
CROSS_FEEDINGL. bulgaricus proteolysis supplies peptides and amino acids that support S. thermophilus in milk. The CNRZ1066/ATCC BAA-365 experiments support this contribution but show that it does not satisfy all sulfur and branched-chain amino-acid demands. LMG 18311/ATCC 11842 expression responses are contextual evidence, not a direct nitrogen-flux measurement or proof of reciprocal final growth benefit.
Source Taxon: Lactobacillus delbrueckii subsp. bulgaricus
Target Taxon: Streptococcus thermophilus
Metabolites: peptide (CHEBI:16670 · MediaIngredientMech · CMMMech), amino acid (CHEBI:33709 · MediaIngredientMech · CMMMech)
Biological Processes:
- fermentation (GO:0006113 · PathwayMech)
- interspecies interaction between organisms (GO:0044419 · PathwayMech)
HYPOTHESIZED mediation: nitrogen support can sustain S. thermophilus growth and hence potential return metabolites. The cited strain-pair experiments do not selectively establish proteolysis as the cause of formate/CO2 return flow; this is not a demonstrated universal feedback loop.
Evidence
-
PMID:20889781 - SUPPORT (IN_VITRO)"Proteolysis by L. bulgaricus supplies both strains with amino acids"
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PMID:19114510 - PARTIAL (IN_VITRO)"implicated mainly in the metabolism of nitrogen"
Urease-Dependent Acidification Acceleration
Urease-deficient S. thermophilus mutants and supplementation experiments support a contribution of urease to rapid yogurt acidification across the tested strain combinations. Ammonia shortage mainly limits S. thermophilus, whereas CO2 shortage affects responsive L. bulgaricus strains. The culture-level benefit is not equivalent to direct reciprocal benefit of every strain pair; ammonia effects were stronger and coculture could mask the deficiency.
Participating Taxa: Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus
Biological Processes:
- fermentation (GO:0006113 · PathwayMech)
Evidence
-
PMID:30594386 - SUPPORT (IN_VITRO)"urease deficiency inhibits the fermentative acceleration of protocooperation"
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PMID:30594386 - SUPPORT (IN_VITRO)"NH3 and CO2 that it generates"
Streptococcus Nox-Dependent Milk Fermentation
In the S. thermophilus 1131/L. bulgaricus 2038 pair, disrupting S. thermophilus nox reduced oxygen removal and slowed skim-milk acidification. Pre-fermentation deoxygenation mainly accelerated early S. thermophilus growth and formate/lactate accumulation, not L. bulgaricus growth; final Streptococcus counts converged. This is a fermentation phenotype, not colonization facilitation. A direct Nox-to-Pfl mechanism remains HYPOTHESIZED.
Participating Taxa: Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus
Biological Processes:
- fermentation (GO:0006113 · PathwayMech)
PARTIAL: Oxygen removal promotes early formate accumulation in the 1131/2038 system, and the nox mutant lacks detected formate in the tested monoculture. Protection of oxygen-sensitive Pfl is HYPOTHESIZED; the study also considers other Nox functions and does not establish the CO2 branch or universal transfer to L. bulgaricus.
Evidence
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PMID:24936380 - SUPPORT (IN_VITRO)"dissolved oxygen (DO) suppresses yogurt fermentation"
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PMID:24936380 - SUPPORT (IN_VITRO)"Nox of S. thermophilus 1131 contributes greatly to yogurt fermentation"
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PMID:24936380 - SUPPORT (IN_VITRO)"deoxygenated fermentation primarily increased the cell number of S. thermophilus 1131 rather than that of L. bulgaricus 2038"
Associated Datasets
| Dataset | Type | Repository | Accession |
|---|---|---|---|
|
Exact-composition publication - urease in yogurt protocooperation
Study of S. thermophilus and L. delbrueckii subsp. bulgaricus strain combinations showing that urease supports acidification in the two-species yogurt starter community. |
PHENOTYPE | OTHER | PMID:30594386 |
|
Exact-composition publication - S. thermophilus 1131 and L. bulgaricus 2038
Study of oxygen removal and NADH oxidase in a yogurt starter composed of S. thermophilus 1131 and L. delbrueckii subsp. bulgaricus 2038. |
PHENOTYPE | OTHER | PMID:24936380 |
|
Exact-composition publication - S. thermophilus LMG 18311 and L. bulgaricus ATCC 11842
Transcriptomic and proteomic analysis of S. thermophilus LMG 18311 cocultured in milk with L. delbrueckii subsp. bulgaricus ATCC 11842. |
METATRANSCRIPTOMICS | OTHER | PMID:19114510 |
|
Exact-composition publication - mixed-culture transcriptome in milk
Mixed-culture transcriptome study of S. thermophilus CNRZ1066 and L. bulgaricus ATCC BAA-365 during batch mixed-culture growth in milk. |
METATRANSCRIPTOMICS | OTHER | PMID:20889781 |
|
Exact-composition publication - genomic protocooperation analysis
Comparative-genomics analysis of L. bulgaricus and S. thermophilus that frames yogurt manufacturing as a two-species protocooperative system. |
OTHER | OTHER | PMID:19395564 |
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which return-flow mechanisms and benefits hold for each tested strain pair and growth stage?
Keep the CNRZ1066/ATCC BAA-365 nutritional model, LMG 18311/ATCC 11842 expression study, 1131/2038 Nox experiment and urease strain panel separate. In the LMG 18311 pair, faster acidification accompanied lower final lactobacillus counts. In the Nox study, early effects did not imply a higher final Streptococcus yield. Nutrient supplementation and knockout phenotypes remain positive evidence without universal mutualism or proven mediation.
Attaches to: ecological_interactions#Streptococcus Formate and Carbon Dioxide Support, ecological_interactions#Lactobacillus Proteolytic Nitrogen Support, ecological_interactions#Urease-Dependent Acidification Acceleration, ecological_interactions#Streptococcus Nox-Dependent Milk Fermentation
1 evidence item(s)
the coculture resulted in a threefold decrease of the final bacterial counts
Faster coculture acidification did not imply a final population benefit to both partners.
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| milk substrate | skim milk or milk used for thermophilic yogurt fermentation | N/A |
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| dissolved oxygen | dissolved oxygen suppresses fermentation; S. thermophilus removes oxygen through NADH oxidase | N/A |
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| ammonia and carbon dioxide from urease | urease-generated NH3 and CO2 affect yogurt acidification | N/A |
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Growth Media
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