A four-member tomato-root SynCom assembled from calcium-enriched antagonists to suppress Ralstonia solanacearum bacterial wilt. Bi et al. isolated Dyella japonica, Rhodanobacter glycinis, Paenibacillus polymyxa, and Pseudomonas aeruginosa from tomato roots after calcium chloride amendment, selected them because they antagonized R. solanacearum, were promoted by calcium or calcium-induced root metabolites, and encoded plant-growth-promoting traits, and mixed OD600-normalized LB-grown suspensions 1:1:1:1. In 96-well root-exudate co-culture assays, the SynCom plus exudates from 20 mM calcium-treated tomato seedlings reduced R. solanacearum density; in greenhouse soil, the SynCom combined with a reduced 100 mg Ca kg-1 soil dose dropped bacterial wilt incidence from 74.07% to 0%.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Dyella japonica | NCBITaxon:231455 · TaxonMech · TraitMech |
PATHOGEN_ANTAGONIST
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DOMINANT |
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| Rhodanobacter glycinis | NCBITaxon:582702 · TaxonMech · TraitMech |
PATHOGEN_ANTAGONIST
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DOMINANT |
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| Paenibacillus polymyxa | NCBITaxon:1406 · TaxonMech · TraitMech |
PATHOGEN_ANTAGONIST
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DOMINANT |
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| Pseudomonas aeruginosa | NCBITaxon:287 · TaxonMech · TraitMech |
PATHOGEN_ANTAGONIST
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DOMINANT |
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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.
Calcium and root-metabolite selective promotion
Separate growth assays found that calcium chloride and tested salicylic-acid, sucrose or trehalose concentrations differentially affected R. solanacearum and beneficial isolates. These are abiotic/compound responses, not measured interorganism colonization facilitation. Calcium-treated root-tissue metabolomics does not establish the same concentrations or mediators in whole exudates or low-dose pots.
Metabolites: salicylic acid (CHEBI:16914 · MediaIngredientMech · CMMMech), sucrose (CHEBI:17992 · MediaIngredientMech · CMMMech), trehalose (CHEBI:27082 · MediaIngredientMech · CMMMech)
HYPOTHESIZED - calcium-associated metabolites could contribute to selective effects of whole root exudates. Purified-compound assays and tissue metabolomics motivate this mechanism, but no selective depletion/add-back test establishes the compounds as necessary exudate mediators.
Evidence
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PMID:41387930 - SUPPORT (IN_VITRO)"Ca supplementation significantly (one-way ANOVA: p < 0.05) inhibited the growth of R. solanacearum while enhancing the growth of the four beneficial strains"
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PMID:41387930 - SUPPORT (IN_VITRO)"higher concentrations of key metabolites (SA, sucrose, and trehalose) inhibited the growth of R. solanacearum and simultaneously promoted the proliferation of beneficial microbes"
Calcium-conditioned root-exudate pathogen suppression
Whole root exudates from seedlings treated with 20 mM calcium, combined with SynCom in 1/2 NB, reduced the reported Ralstonia qPCR abundance. Gene copies are not viable-cell counts. The outcome does not establish reciprocal-negative competition, a unique compound mediator or the cause of disease protection in a separate low-dose pot assay.
Evidence
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PMID:41387930 - SUPPORT (IN_VITRO)"whole root exudates from Ca-treated plants (20 mM) significantly inhibited R. solanacearum growth while promoting the growth of beneficial microbes such as Paenibacillus polymyxa"
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PMID:41387930 - SUPPORT (IN_VITRO)"the addition of whole root exudates from 20 mM Ca-treated plants led to a significant reduction in R. solanacearum density"
Calcium-SynCom bacterial wilt control
Adding SynCom one week after pathogen challenge together with 100 mg Ca kg-1 soil reduced observed tomato wilt incidence from 74.07% to 0% in the controlled pot experiment. This is disease-incidence protection, not demonstrated pathogen eradication or reciprocal mutualism. One-way treatment comparisons do not alone establish formal factorial synergy, and high-dose root-defense assays are not isolated mediators of this low-dose result.
Evidence
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PMID:41387930 - SUPPORT (IN_VIVO)"with wilt incidence dropping from 74.07 to 0%"
Associated Datasets
| Dataset | Type | Repository | Accession |
|---|---|---|---|
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Bi et al. calcium-tomato root microbiome and isolate genome reads
BioProject holding raw 16S rRNA amplicon sequencing data for the calcium gradient experiment; the same data-availability statement reports raw genome reads for the four SynCom isolates under SRR33220703, SRR33220740, SRR33221449, and SRR33221452. |
GENOMICS | NCBI_BIOPROJECT | PRJNA1125171 |
Knowledge gaps & discussions (2)
KNOWLEDGE_GAP OPEN Which SynCom members directly drive the Ralstonia solanacearum density drop in calcium-conditioned tomato root exudate, and is suppression mediated by antibiotic antagonism, calcium/root-metabolite competition, or both?
Bi et al. showed that all four isolates antagonized Ralstonia solanacearum and that the SynCom plus calcium-conditioned tomato root exudates reduced Ralstonia density. The paper also reports pairwise plate assays and predicted plant-growth-promoting genes, but it did not resolve member-to-member metabolic exchange or show which SynCom strain directly caused the Ralstonia drop in root-exudate co-culture. Barcode-tracked single, triple-dropout, and full four-member SynComs in the 20 mM calcium-conditioned root-exudate assay would resolve the member-level contributions.
Attaches to: ecological_interactions
KNOWLEDGE_GAP OPEN Which calcium, exudate and host pathways are necessary for the low-dose SynCom pot benefit?
Retain the compound-to-exudate interpretation only as HYPOTHESIZED; remove the cross-assay exudate-to-pot arrow. Direct calcium effects, host defense and microbial selection remain concurrent alternatives. Root-tissue metabolites, whole-exudate growth and pot disease are distinct assays; relative ASVs do not prove exact-strain colonization. Full main text/captions read, not images or supplements. Preserve #961-963 and existing gaps; non-graph synergy/dominance/environment wording remains #1268.
Attaches to: ecological_interactions#Calcium and root-metabolite selective promotion, ecological_interactions#Calcium-conditioned root-exudate pathogen suppression, ecological_interactions#Calcium-SynCom bacterial wilt control
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| defined 1:1:1:1 bacterial SynCom inoculum | Dyella japonica, Rhodanobacter glycinis, Paenibacillus polymyxa, and Pseudomonas aeruginosa | N/A |
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| calcium-conditioned whole root exudates | 20 mM Ca as CaCl2 | N/A |
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| low-dose calcium biocontrol pot treatment | 100 mg Ca kg-1 soil plus SynCom | N/A |
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Growth Media
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