Two-species synthetic bacterial community (SynCom Y) of Agrobacterium deltaense LSQ16 and Bacillus velezensis WB, simplified from a larger biocontrol SynCom Q by stepwise strain omission. Co-cultivation synergistically enhances multispecies biofilm formation, extracellular polysaccharide production, and metabolic activity, improving suppression of watermelon Fusarium wilt. Genome-scale modeling predicts interspecies metabolite exchange (amino acids, purines, phosphates); exogenous L-ornithine and guanine enhance B. velezensis biofilm formation, consistent with cross-feeding-supported cooperation.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Agrobacterium deltaense LSQ16 — ontology label: Agrobacterium deltae | NCBITaxon:1183412 · TaxonMech · TraitMech |
CROSS_FEEDER
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N/A |
|
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| Bacillus velezensis WB — ontology label: Bacillus velezensis | NCBITaxon:492670 · TaxonMech · TraitMech |
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.
Synergistic biofilm and EPS formation in co-culture
MUTUALISMCo-culture increased biofilm biomass, EPS and metabolic activity relative to monocultures. Species-specific qPCR also supported increased cell-equivalent abundance of both strains in the biofilm fraction, supporting reciprocal benefit in that assay. WB abundance did not increase in the planktonic fraction. This conditional biofilm mutualism is not proof of reciprocal metabolite delivery or of the same interaction operating on watermelon roots.
Source Taxon: Agrobacterium deltaense LSQ16
Target Taxon: Bacillus velezensis WB
Biological Processes:
- biofilm formation (GO:0042710 · PathwayMech)
HYPOTHESIZED/PARTIAL: enhanced EPS-rich biofilm formation could contribute to fusaric-acid tolerance and the positive pot-level biocontrol outcome. Separate in-vitro and pot comparisons do not isolate biofilm mediation or establish that the in-vitro partnership occurs in the rhizosphere.
Evidence
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PMID:42125264 - SUPPORT (IN_VITRO)"Compared with monocultures, co-cultivation also markedly increased extracellular polysaccharide production and metabolic activity."
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PMID:42125264 - SUPPORT (IN_VITRO)"Quantitative PCR under co-culture conditions confirmed that mixed-species biofilm formation promotes the growth of both strains"
SynCom Y Fusaric Acid and Wilt Resistance
The two-strain biofilm tolerated fusaric-acid exposure better than either monoculture in vitro. Separately, SynCom Y reduced watermelon wilt in pots, with reported disease incidence 18.33% and control efficacy 79.13%. Preserve both positive outcomes without equating biofilm tolerance with pathogen killing or asserting that EPS, a specific exchanged metabolite or root colonization was experimentally isolated as the cause of disease suppression.
Participating Taxa: Agrobacterium deltaense LSQ16, Bacillus velezensis WB
Metabolites: fusaric acid (CHEBI:5199 · MediaIngredientMech · CMMMech)
Evidence
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PMID:42125264 - SUPPORT (IN_VITRO)"The two-strain biofilm showed a notable biomass decrease at 17 μg/mL FA, indicating enhanced resistance to FA compared with single-species biofilms"
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PMID:42125264 - SUPPORT (IN_VIVO)"The SynCom Y, composed of A. deltaense LSQ16 and B. velezensis WB, exhibited a disease incidence of 18.33% and a control efficacy of 79.13%"
Predicted cross-feeding from A. deltaense LSQ16 to B. velezensis WB
CROSS_FEEDINGHYPOTHESIZED/PARTIAL: genome-scale models predict LSQ16-to-WB exchange of several metabolites. Exogenous L-ornithine and guanine increased WB biofilm biomass, and co-culture metabolite abundances were consistent with the proposed direction. Supplementation demonstrates a physiological response, not direct donor-to-recipient transfer. Malate and guanosine were also included in supplementation tests; the reported positive validation centers on ornithine and guanine. Other predicted exchanges are not established measured fluxes.
Source Taxon: Agrobacterium deltaense LSQ16
Target Taxon: Bacillus velezensis WB
Metabolites: L-ornithine (CHEBI:15729 · MediaIngredientMech · CMMMech), guanine (CHEBI:16235 · MediaIngredientMech · CMMMech), guanosine (CHEBI:16750 · MediaIngredientMech · CMMMech), (S)-malate (CHEBI:15589 · MediaIngredientMech · CMMMech), phosphate (CHEBI:26020 · MediaIngredientMech · CMMMech)
HYPOTHESIZED/PARTIAL: predicted LSQ16 provision of L-ornithine and guanine could contribute to WB biofilm enhancement, consistent with the positive additions and metabolite profiles. These results do not establish transfer, its necessity, or its quantitative contribution to the two-strain biofilm/EPS response.
Evidence
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PMID:42125264 - PARTIAL (IN_VITRO)"Moreover, exogenous supplementation of l-ornithine and guanine further enhanced the biofilm-forming capacity of B. velezensis WB."
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PMID:42125264 - PARTIAL (COMPUTATIONAL)"A. deltaense LSQ16 may supply malate, O-acetylcarnitine, guanine, guanosine, l-ornithine, and phosphate to B. velezensis WB"
Predicted metabolite return from B. velezensis WB to A. deltaense LSQ16
CROSS_FEEDINGHYPOTHESIZED/PARTIAL: models predict WB-to-LSQ16 return of L-serine, pyroglutamic acid, myristic acid and suberoylglycine. Metabolite abundance patterns are consistent with some predictions, but additions of tested reverse-direction candidates did not significantly enhance LSQ16 monoculture biofilm biomass. This negative endpoint does not prove that exchange is absent; it prevents describing a beneficial return flux as experimentally validated.
Source Taxon: Bacillus velezensis WB
Target Taxon: Agrobacterium deltaense LSQ16
Metabolites: L-serine (CHEBI:17115 · MediaIngredientMech · CMMMech)
Evidence
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PMID:42125264 - PARTIAL (COMPUTATIONAL)"which in turn provides suberoylglycine, myristic acid, l-serine, and pyroglutamic acid to A. deltaense LSQ16"
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PMID:42125264 - PARTIAL (IN_VITRO)"the addition of l-serine, pyroglutamic acid, and other compounds did not result in a significant enhancement of the biofilm biomass in A. deltaense LSQ16 monocultures"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which predicted exchanges mediate biofilm synergy and the pot-level biocontrol outcome?
Preserve reciprocal biofilm-associated abundance, EPS, metabolic activity, FA tolerance and disease suppression. Forward additions are positive; tested reverse additions did not significantly enhance LSQ16 biofilm. Neither result directly measures interspecies transfer. The primary discussion explicitly leaves rhizosphere synergy unverified. Modeling methods name CarveMe, Cobra toolbox and FBA but do not state versions or genome input accessions; the cited SRA range belongs to RNA-seq. Main text and captions were read, not separate supplementary data or raw datasets.
Attaches to: ecological_interactions#Synergistic biofilm and EPS formation in co-culture, ecological_interactions#SynCom Y Fusaric Acid and Wilt Resistance, ecological_interactions#Predicted cross-feeding from A. deltaense LSQ16 to B. velezensis WB, ecological_interactions#Predicted metabolite return from B. velezensis WB to A. deltaense LSQ16
1 evidence item(s)
Whether the two strains form a synergistic relationship in the rhizosphere still requires validation via root colonization assays.
Explicit limitation separating in-vitro biofilm findings from rhizosphere mechanism.
Growth Media
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