A top-down three-strain synthetic microbial consortium from Viili fermented milk, composed of Lactococcus lactis V9, Lacticaseibacillus paracasei V21, and Geotrichum candidum Y1. Hu et al. 2026 used monoculture, co-culture, supernatant-supplementation, metabolomics, amino-acid depletion, amino-acid supplementation, and AI-2 perturbation assays to show that G. candidum supplies lactic-acid bacteria with nitrogen sources including valine, increases AI-2/luxS quorum-sensing activity, and gives the three-member community the highest measured exopolysaccharide concentration among the tested microbial combinations.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Lactococcus lactis V9 — ontology label: Lactococcus lactis | NCBITaxon:1358 · TaxonMech · TraitMech |
SECONDARY_FERMENTER
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N/A |
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| Lacticaseibacillus paracasei V21 — ontology label: Lacticaseibacillus paracasei | NCBITaxon:1597 · TaxonMech · TraitMech |
SECONDARY_FERMENTER
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N/A |
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| Geotrichum candidum Y1 — ontology label: Geotrichum candidum | NCBITaxon:1173061 · TaxonMech · TraitMech |
CROSS_FEEDER
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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.
Geotrichum nitrogen supply to lactic acid bacteria
CROSS_FEEDINGG. candidum Y1 supplies nitrogen sources, including valine, to L. lactis V9 and L. paracasei V21. Metabolomics and amino-acid depletion/supplementation support nutrient provision associated with increased bacterial growth, biofilm formation and EPS production. These assays do not by themselves isolate a valine-specific signaling mechanism independent of growth.
Participating Taxa: Geotrichum candidum Y1, Lactococcus lactis V9, Lacticaseibacillus paracasei V21
Metabolites: valine (CHEBI:27266 · MediaIngredientMech · CMMMech), amino acid (CHEBI:33709 · MediaIngredientMech · CMMMech)
PARTIAL: fungal nitrogen provision supports bacterial growth and is accompanied by stronger quorum-sensing activity. It may contribute to activation of the AI-2 regulatory node, but the abstract does not isolate valine-specific mediation from growth effects.
Evidence
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PMID:42372608 - SUPPORT (IN_VITRO)"Untargeted metabolomics combined with validation experiments revealed that G. candidum supplied lactic acid bacteria with nitrogen sources, including valine."
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PMID:42372608 - SUPPORT (IN_VITRO)"Amino acid depletion and supplementation experiments indicated that valine, as a key amino acid, is closely associated with enhanced growth, biofilm formation, and EPS production in lactic acid bacteria."
AI-2 regulation of Viili bacterial EPS production
Fungal co-culture increases bacterial AI-2 production and luxS transcription. AI-2 activation and inhibition assays support positive regulation of EPS synthesis. This is signaling regulation, not evidence that G. candidum supplies AI-2 as an exchanged nutrient; the abstract describes fungal-metabolite activation of signaling as a possible contribution.
Participating Taxa: Geotrichum candidum Y1, Lactococcus lactis V9, Lacticaseibacillus paracasei V21
Metabolites: AI-2 (CHEBI:40646 · MediaIngredientMech · CMMMech), exopolysaccharide (CHEBI:72813 · MediaIngredientMech · CMMMech)
Biological Processes:
- quorum sensing (GO:0009372 · PathwayMech)
AI-2 activation and inhibition support positive regulation of bacterial EPS synthesis and thus a contribution to the three-member output. They do not establish AI-2 as the sole explanation of the tested consortium maximum.
Evidence
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PMID:42372608 - SUPPORT (IN_VITRO)"co-culture with G. candidum significantly enhanced AI-2 production and luxS gene transcription in lactic acid bacteria."
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PMID:42372608 - SUPPORT (IN_VITRO)"AI-2 activation and inhibition assays confirmed that AI-2-mediated quorum sensing positively regulates EPS synthesis."
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PMID:42372608 - PARTIAL (IN_VITRO)"fungal metabolites may contribute to the activation of AI-2 signaling"
Three-species Viili EPS maximum
Among the microbial combinations tested in the Viili model, the complete L. lactis V9 plus L. paracasei V21 plus G. candidum Y1 consortium had the highest measured exopolysaccharide concentration.
Participating Taxa: Lactococcus lactis V9, Lacticaseibacillus paracasei V21, Geotrichum candidum Y1
Metabolites: exopolysaccharide (CHEBI:72813 · MediaIngredientMech · CMMMech)
Evidence
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PMID:42372608 - SUPPORT (IN_VITRO)"the three-species consortium (L. lactis V9 + L. paracasei V21 + G. candidum Y1) exhibited the highest EPS concentration among all tested microbial combinations, reaching 1.09 mg/mL."
Knowledge gaps & discussions (2)
KNOWLEDGE_GAP OPEN Which Viili media, incubation parameters, inoculation ratios, and original isolation details were used for strains V9, V21, and Y1?
The PubMed/Europe PMC abstract names the strains and assays but the International Journal of Food Microbiology full Methods text was not legally open during initial curation, so medium composition, inoculation ratios, temperature, and original isolate sources remain uncited.
Attaches to: growth_media, taxonomy
KNOWLEDGE_GAP OPEN Does fungal valine activate AI-2 signaling independently of its effect on bacterial growth?
The abstract reports nutrient depletion/supplementation and AI-2 perturbation assays, but the inspected source does not isolate the full nitrogen-to-signaling mediation chain. Full methods and growth-matched signaling perturbations are needed to resolve this link. The measured nutrient, AI-2 and EPS responses remain supported.
Attaches to: ecological_interactions#Geotrichum nitrogen supply to lactic acid bacteria, ecological_interactions#AI-2 regulation of Viili bacterial EPS production, ecological_interactions#Three-species Viili EPS maximum
1 evidence item(s)
fungal metabolites may contribute to the activation of AI-2 signaling
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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PubMed - Viili fungus-bacterium EPS SynCom
PubMed record for the 2026 International Journal of Food Microbiology article describing the three-strain Viili synthetic microbial consortium. |
OTHER | PMID:42372608 |
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DOI - Viili fungus-bacterium EPS SynCom
DOI for the 2026 International Journal of Food Microbiology article describing fungus-bacterium metabolic interactions in a Viili SynCom. |
OTHER | doi:10.1016/j.ijfoodmicro.2026.111922 |
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