A defined four-strain plant growth-promoting bacterial (PGPB) consortium designed for space-agriculture (In-Situ Resource Utilization) research, composed of Azotobacter chroococcum 76A, Priestia megaterium EL5, Methylobacterium populi VP2, and Kosakonia pseudosacchari TL13. The strains belong to the microbial collection of the Department of Agricultural Sciences of the University of Naples Federico II and were selected for complementary plant growth-promoting traits (nitrogen fixation, phosphate solubilization, phytohormone biosynthesis) and for mutual non-antagonism in dual-culture assays. In a greenhouse pot experiment, the consortium was combined with green compost derived from plant residues (pH 8.25, low C/N ratio) to improve lettuce (Lactuca sativa cv. Grand Rapids) growth on commercial Lunar (LHS-1) and Martian (MMS-1) regolith simulants with zero external chemical input aside from the compost. Compost amendment increased lettuce biomass and nutrient bioavailability, and PGPB inoculation enhanced leaf biomass and mineral nutritional content while significantly increasing the copy number of functional marker genes for nitrogen fixation (nifH), alkaline phosphatase (phoD), and phytase (BPP) in non-amended substrates. The system is a Bioregenerative Life Support System model relevant to regolith-agriculture and long-term space missions.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Azotobacter chroococcum 76A — ontology label: Azotobacter chroococcum | NCBITaxon:353 · TaxonMech · TraitMech | N/A | |
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| Priestia megaterium EL5 — ontology label: Priestia megaterium | NCBITaxon:1404 · TaxonMech · TraitMech | N/A | |
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| Methylobacterium populi VP2 — ontology label: Methylorubrum populi | NCBITaxon:223967 · TaxonMech · TraitMech | N/A | |
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| Kosakonia pseudosacchari TL13 — ontology label: Kosakonia pseudosacchari | NCBITaxon:1646340 · 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.
PGPB Dual-Culture Compatibility Screen
The four inoculant strains were selected after dual-culture screening found no inhibition zones. This is assay-specific compatibility, not demonstrated commensalism, universal non-antagonism or stable coexistence in the lettuce rhizosphere. Individual-strain fermentor production and subsequent assembly are preparation steps, not evidence that screening caused establishment or plant benefit.
Participating Taxa: Azotobacter chroococcum 76A, Priestia megaterium EL5, Methylobacterium populi VP2, Kosakonia pseudosacchari TL13
Biological Processes:
- interspecies interaction between organisms (GO:0044419 · PathwayMech)
Evidence
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doi:10.1007/s00374-025-01923-3 - SUPPORT (IN_VITRO)"absence of antagonism, assessed"
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doi:10.1007/s00374-025-01923-3 - SUPPORT (IN_VITRO)"of inhibition zones were used for consortium"
PGPB-Associated Rhizosphere Functional-Gene Copies
After inoculation of living lettuce grown in an Earth greenhouse, rhizosphere DNA qPCR showed increased nifH, phoD and BPP gene copies in non-amended substrates; amended simulants did not show significant inoculum-associated differences. These are gene-copy measurements, not expression, nitrogen-fixation flux or phosphate release. Community metabarcoding could not distinguish environmental from inoculated strains, so establishment of each inoculant and gene ownership remain unresolved. The four listed participants are the applied consortium, not the entire rhizosphere or missing canonical lettuce host.
Participating Taxa: Azotobacter chroococcum 76A, Priestia megaterium EL5, Methylobacterium populi VP2, Kosakonia pseudosacchari TL13
Biological Processes:
- nitrogen fixation (GO:0009399 · PathwayMech)
Evidence
-
doi:10.1007/s00374-025-01923-3 - SUPPORT (IN_VIVO)"significantly increased the relative abundances"
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doi:10.1007/s00374-025-01923-3 - SUPPORT (IN_VIVO)"increase in functional genes linked with nitrogen fixation and phosphorus"
PGPB-enhanced lettuce growth and mineral nutrition
In the factorial Earth-greenhouse experiment, PGPB treatment increased lettuce leaf dry biomass by35% overall and mineral nutrient content by26% on average. These are treatment-level summaries, not identical benefits in every substrate or nutrient. Nutrient concentrations increased significantly only for P and K; total content also reflects biomass, and no significant overall inoculum effect on chemically extracted substrate nutrient availability was detected. The positive plant endpoints do not establish IAA mediation, fixed-nitrogen delivery, reciprocal microbial benefit or performance under lunar or Martian environmental conditions. The listed taxa are inoculants; the host and background microbiome are not represented by that list.
Participating Taxa: Azotobacter chroococcum 76A, Priestia megaterium EL5, Methylobacterium populi VP2, Kosakonia pseudosacchari TL13
Biological Processes:
- biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)
Evidence
-
doi:10.1007/s00374-025-01923-3 - SUPPORT (IN_VIVO)"PGPB treatment enhanced leaf biomass by 35%"
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doi:10.1007/s00374-025-01923-3 - SUPPORT (IN_VIVO)"microbial consortium could exert positive impact on plants grown in nutrient-limited substrates"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which organisms and activities mediate the positive plant response?
Preserve compatibility-screen, gene-copy and plant-outcome nodes; drop both preparation/mediation arrows. No inhibition zone does not establish commensalism or stable coexistence. DNA copies and limited-resolution amplicon profiles do not prove inoculant establishment, expression, gene ownership or nutrient flux. Marker increases are conditioned on amendment status; biomass/content benefits do not identify selective IAA or nutrient mediation, and chemically extracted nutrient availability had no significant overall inoculum effect. Main body and embedded captions were read, not linked table cells, original figures, supplementary DOCX or raw sequence data; numerical summaries are author-reported, not independently recomputed. Earth greenhouse simulants are not actual extraterrestrial environments. #1559 tracks the missing canonical host and non-graph background/mechanism/environment conflations; #543 already fixed per-strain fermentor wording.
Attaches to: ecological_interactions#PGPB Dual-Culture Compatibility Screen, ecological_interactions#PGPB-Associated Rhizosphere Functional-Gene Copies, ecological_interactions#PGPB-enhanced lettuce growth and mineral nutrition
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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Primary publication - PGPB consortia and green compost on regolith simulants
Duri et al. 2025, Biology and Fertility of Soils - primary source describing the four-strain PGPB consortium and green compost improving lettuce growth on Lunar and Martian regolith simulants. |
OTHER | doi:10.1007/s00374-025-01923-3 |
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NCBI Taxonomy - Azotobacter chroococcum
NCBI Taxonomy record for Azotobacter chroococcum. |
OTHER | NCBITaxon:353 |
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NCBI Taxonomy - Priestia megaterium
NCBI Taxonomy record for Priestia megaterium. |
OTHER | NCBITaxon:1404 |
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NCBI Taxonomy - Methylorubrum populi
NCBI Taxonomy record for Methylorubrum populi (formerly Methylobacterium populi). |
OTHER | NCBITaxon:223967 |
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NCBI Taxonomy - Kosakonia pseudosacchari
NCBI Taxonomy record for Kosakonia pseudosacchari. |
OTHER | NCBITaxon:1646340 |
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Regolith simulant substrate | Lunar Highlands Simulant (LHS-1) and Mojave Mars Simulant (MMS-1) | N/A |
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| Regolith alkalinity and nutrient limitation | alkaline pH (9 to 10), organic-matter-poor | N/A |
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| Green compost amendment | green compost, pH 8.25, low C/N ratio, 20% v/v | N/A |
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| Greenhouse climate | mean air temperature 13 C; 10/14 photoperiod | N/A |
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Growth Media
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