A five-strain synthetic consortium of Eucalyptus-derived bacteria — Bacillus subtilis, Paraburkholderia caribensis, Methylobacterium tardum, and two strains representing putative novel species in Paenibacillus and Mesorhizobium — assembled from isolates of Eucalyptus rhizosphere and roots and selected for complementary functional traits in nitrogen cycling and rhizosphere colonisation. Applied to three Eucalyptus clones in a large tree-nursery field experiment and assessed after 13 weeks, the inoculant did not change bacterial richness or diversity but did alter root microbial community structure; two genotypes showed improved seedling quality and one showed mortality fall from 21.8% to 6.7%. The record captures a case where a defined inoculant reshapes community composition and host outcome without shifting diversity metrics, and where the response is genotype-dependent rather than uniform.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
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| Bacillus subtilis | NCBITaxon:1423 · TaxonMech · TraitMech | N/A | |
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| Paraburkholderia caribensis | NCBITaxon:75105 · TaxonMech · TraitMech | N/A | |
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| Methylobacterium tardum | NCBITaxon:374432 · TaxonMech · TraitMech | N/A | |
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| Paenibacillus sp. (putative novel species) — ontology label: Paenibacillus | NCBITaxon:44249 · TaxonMech · TraitMech | N/A | |
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| Mesorhizobium sp. (putative novel species) — ontology label: Mesorhizobium | NCBITaxon:68287 · TaxonMech · TraitMech | N/A | |
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| Eucalyptus (three clones) — ontology label: Eucalyptus | NCBITaxon:3932 · TaxonMech · TraitMech | 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.
Complementary Nitrogen-Phosphate Trait Pool
The five bacterial inoculant members were selected using prior phosphate-solubilization screens, with nifH detected and indolic compounds produced by some candidates. These prior traits do not demonstrate nitrogen fixation in the nursery, specific indole-3-acetic acid exchange or persistence of each inoculant. The participants name the inoculant, not every member of the native root microbiome.
Participating Taxa: Bacillus subtilis, Paraburkholderia caribensis, Methylobacterium tardum, Paenibacillus sp. (putative novel species), Mesorhizobium sp. (putative novel species)
Metabolites: phosphate (CHEBI:18367 · MediaIngredientMech · CMMMech)
Evidence
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PMID:42050290 - SUPPORT (IN_VITRO)"These bacteria were selected for their strong performance in phosphate solubilization tests, and some exhibited the presence of the nifH gene (indicating potential nitrogen-fixing capacity) as well as the production of indolic compounds"
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PMID:42050290 - SUPPORT (IN_VIVO)"direct nitrogen fixation was not measured in this study"
Root Endophytic Community Restructuring
At 13 weeks, inoculation changed root community structure by PERMANOVA without significantly changing richness or Shannon diversity. No genus or phylum showed robust differential abundance after ANCOM-BC-2 sensitivity analysis; reported Mesorhizobium enrichment and Ralstonia reduction are exploratory, not proof of inoculant persistence or disease suppression. Endpoint profiles of 30 A/B-category seedlings do not resolve strain-specific colonization through time. Participants identify inoculant plus host context, not an exhaustive root community.
Participating Taxa: Bacillus subtilis, Paraburkholderia caribensis, Methylobacterium tardum, Paenibacillus sp. (putative novel species), Mesorhizobium sp. (putative novel species), Eucalyptus (three clones)
Evidence
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PMID:42050290 - SUPPORT (IN_VIVO)"While inoculation did not significantly affect bacterial richness and diversity, it altered the root microbial community structure"
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PMID:42050290 - SUPPORT (COMPUTATIONAL)"No taxa were identified as robustly differentially abundant after ANCOM-BC-2 sensitivity analysis"
Genotype-Dependent Improvement of Seedling Quality and Survival
The nursery trial compared five-strain inoculation with a water control across three Eucalyptus genotypes. At 13 weeks, quality improvements were genotype-dependent: the reported nonviable/dead category fell from 21.8% to 6.7% for genotype Y, and genotype Z had improved quality. The operational dead category also included severe stem curvature greater than 45 degrees, so this is not exclusively literal mortality. Morphological responses were not uniformly positive across genotypes and traits. Host outcomes do not establish reciprocal bacterial fitness or a resolved microbial mediator.
Participating Taxa: Bacillus subtilis, Paraburkholderia caribensis, Methylobacterium tardum, Paenibacillus sp. (putative novel species), Mesorhizobium sp. (putative novel species), Eucalyptus (three clones)
Biological Processes:
- growth (GO:0040007 · PathwayMech)
Evidence
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PMID:42050290 - SUPPORT (IN_VIVO)"Two genotypes exhibited improved seedling quality, with a higher proportion classified into superior categories, and one genotype showed a significant reduction in mortality (from 21.8% to 6.7%)"
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PMID:42050290 - SUPPORT (IN_VIVO)"Seedlings exhibiting severe stem curvature (defined as a deviation greater than 45° from the vertical axis) or found dead during the evaluation period were counted as dead"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which inoculant functions mediate the genotype-dependent nursery response?
Prior trait screens do not establish nursery nitrogen fixation or specific IAA flux. Root compositional change does not demonstrate persistence of each inoculant; differential taxon trends were not robust after sensitivity analysis. Host quality is genotype-dependent and the dead category includes severe stem curvature. Preserve both workflow-arrow removals from 2026-10-02: none of these observations resolves a mediator linking traits, root composition and host outcome. The control received water; the trial does not isolate PBS-carrier effects. Canonical five-member inoculant and Eucalyptus host labels are preserved, including AMBIGUOUS Paenibacillus grounding. Non-graph fields are preserved, not certified.
Attaches to: ecological_interactions#Complementary Nitrogen-Phosphate Trait Pool, ecological_interactions#Root Endophytic Community Restructuring, ecological_interactions#Genotype-Dependent Improvement of Seedling Quality and Survival
Environmental Factors
| Factor | Value | Unit |
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| Tree-nursery field trial | three Eucalyptus clones; 13 weeks | N/A |
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Growth Media
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