Two-member infant-gut co-culture of Escherichia coli and Bifidobacterium bifidum. In healthy, term-born, breastfed infants these genera co-exist despite differing ecological strategies and share evolutionary adaptations for lactose acquisition. In vitro co-culture demonstrates a mutualistic cross-feeding interaction in which E. coli supplies cysteine to its auxotrophic partner B. bifidum, facilitating cooperative degradation of 2'-fucosyllactose (the predominant human milk oligosaccharide), and the liberated monosaccharides in turn sustain E. coli growth, potentially helping regulate E. coli abundance in the infant gut.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Escherichia coli | NCBITaxon:562 · TaxonMech · TraitMech |
CROSS_FEEDER
SYNTROPHIC_PARTNER
|
N/A |
|
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| Bifidobacterium bifidum | NCBITaxon:1681 · 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.
Cysteine provision enabling cooperative 2'-fucosyllactose degradation
CROSS_FEEDINGIn the nutrient-limited in vitro model, E. coli K12 supplies the cysteine requirement of an infant-stool B. bifidum isolate, enabling growth and 2-fucosyllactose degradation without added cysteine or casamino acids. The delta-cysE donor control impaired coculture growth and ethanol-killed partner controls failed to support it. This supports cysteine-dependent cooperation, not a measured cysteine export rate or proof of active secretion rather than overflow or lysis.
Source Taxon: Escherichia coli
Target Taxon: Bifidobacterium bifidum
Metabolites: cysteine (CHEBI:15356 · MediaIngredientMech · CMMMech), 2'-fucosyllactose (CHEBI:147155 · MediaIngredientMech · CMMMech)
Cysteine-dependent support from E. coli permits the auxotrophic B. bifidum partner to grow and degrade 2-fucosyllactose under the tested nutrient limitation, releasing sugar substrates usable by E. coli. The mutant and killed-partner controls support the dependency; the sugar-consumption assay separately required spent-medium pH adjustment to 6.3.
Evidence
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PMID:42020426 - SUPPORT (IN_VITRO)"E. coli supplies cysteine to its auxotrophic partner, facilitating cooperative degradation of 2'-fucosyllactose, the predominant human milk oligosaccharide"
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PMID:42020426 - SUPPORT (IN_VITRO)"observing a significant impairment of growth"
Monosaccharide return sustaining E. coli growth
CROSS_FEEDINGB. bifidum degraded 2-fucosyllactose and left fucose and galactose that E. coli K12 subsequently consumed, measured by chromatography. E. coli grew in this spent medium only after pH readjustment from 4.3 to 6.3. This measured in vitro return of carbon does not establish that the same exchange controls E. coli abundance in infants or quantify sugar-to-cysteine flux in coculture.
Source Taxon: Bifidobacterium bifidum
Target Taxon: Escherichia coli
Metabolites: monosaccharide (CHEBI:35381 · MediaIngredientMech · CMMMech)
PARTIAL - accessible HMO-derived sugars sustain E. coli growth and can maintain the donor population supporting the cysteine-dependent partner. Reciprocal nutrient dependence is experimentally supported, but a time-resolved sugar-to-cysteine feedback gain or isotope-resolved flux was not measured; the separate spent-medium assay required pH 6.3.
Evidence
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PMID:42020426 - SUPPORT (IN_VITRO)"the liberated monosaccharides sustain E. coli growth, highlighting a cooperative cross-feeding interaction that may contribute to regulating E. coli abundance within the infant host"
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PMID:42020426 - SUPPORT (IN_VITRO)"B. bifidum efficiently degraded 2’FL, but left galactose and fucose unconsumed"
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PMID:42020426 - SUPPORT (IN_VITRO)"growth only when the pH was adjusted to its initial value of 6.3"
Cooperative Infant-Gut HMO Mutualism
MUTUALISME. coli K12 and the infant-stool B. bifidum isolate co-grew in modified M9 with 0.5% 2-fucosyllactose and without added cysteine or casamino acids. Cysteine dependence, viable-partner controls and measured sugar utilization support reciprocal benefit in this restricted laboratory model. This node summarizes that exchange rather than adding a separate downstream outcome. Its prevalence, strength and effect on E. coli abundance in living infants remain untested.
Participating Taxa: Escherichia coli, Bifidobacterium bifidum
Metabolites: cysteine (CHEBI:15356 · MediaIngredientMech · CMMMech), 2'-fucosyllactose (CHEBI:147155 · MediaIngredientMech · CMMMech), monosaccharide (CHEBI:35381 · MediaIngredientMech · CMMMech)
Biological Processes:
- biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)
Evidence
-
PMID:42020426 - SUPPORT (IN_VITRO)"the liberated monosaccharides sustain E. coli growth, highlighting a cooperative cross-feeding interaction that may contribute to regulating E. coli abundance within the infant host"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN How strongly does the measured laboratory exchange operate in the infant gut?
The K12 donor and infant B. bifidum isolate support nutrient-limited reciprocal cooperation, not a universal species-level interaction or demonstrated regulation of E. coli abundance in vivo. Chromatographic sugar data and a delta-cysE control do not resolve cysteine release route, export rate or isotope-resolved feedback. The pH-adjusted spent-medium assay is distinct from the live coculture. The sugar-to-mutualism summary arrow is removed as a part/whole restatement, not an independently supported causal consequence. Experimental-strain and 0.1% screening versus 0.5% coculture metadata remain under #1428.
Attaches to: ecological_interactions#Cysteine provision enabling cooperative 2'-fucosyllactose degradation, ecological_interactions#Monosaccharide return sustaining E. coli growth, ecological_interactions#Cooperative Infant-Gut HMO Mutualism
Growth Media
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