A defined biological soil crust cyanosphere coculture pairing the pioneer cyanobacterium Microcoleus vaginatus PCC 9802 with the heterotrophic cyanosphere isolate Massilia sp. METH4. Across repeated studies of the same exact strain pair, M. vaginatus provides photosynthetically fixed organic carbon while the diazotrophic Massilia partner supports nitrogen acquisition through a specific carbon-for-nitrogen mutualism, including urea-mediated nitrogen transfer and GABA/glutamate signaling that organizes close spatial association.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Microcoleus vaginatus PCC 9802 — ontology label: Microcoleus vaginatus | NCBITaxon:119532 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
CROSS_FEEDER
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DOMINANT |
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| Massilia sp. METH4 — ontology label: Massilia | NCBITaxon:149698 · TaxonMech · TraitMech |
CROSS_FEEDER
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COMMON |
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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.
Carbon-for-Nitrogen Resource Trading
MUTUALISMM. vaginatus PCC 9802 and Massilia sp. METH4 participate in selective carbon-for-nitrogen mutualism: coculture growth under organic-carbon and fixed-nitrogen limitation is consistent with photosynthate supporting the heterotroph and diazotrophic nitrogen acquisition supporting the cyanobacterium. The shared growth phenotype does not by itself identify the transferred organic-carbon compound or quantify partner-specific fluxes.
Source Taxon: Microcoleus vaginatus PCC 9802
Target Taxon: Massilia sp. METH4
Metabolites: carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech)
Biological Processes:
- photosynthesis (GO:0015979 · PathwayMech)
- biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)
Evidence
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PMID:32968213 - SUPPORT (IN_VITRO)"Co-culturing of pedigreed cyanosphere diazotroph isolates with axenic M. vaginatus resulted in copious growth in C and N-free medium"
Urea-Mediated Nitrogen Transfer
CROSS_FEEDINGPARTIAL - Urea is a strongly supported likely nitrogen-transfer vehicle in the exact PCC 9802/METH4 pair. Coculture increases extracellular urea release; METH4 upregulates urea-cycle genes and PCC 9802 upregulates uptake and urea carboxylase/allophanate hydrolase genes. PCC 9802 can grow on supplied urea down to 5 micromolar, but not 2 micromolar in the tested assay. These convergent results support cross-feeding without directly tracing the origin and assimilation of each urea molecule or proving urea is the exclusive nitrogen carrier. Release rates use total coculture biomass, because a heterotrophic origin of extracellular urea is inferred rather than absolutely resolved.
Source Taxon: Massilia sp. METH4
Target Taxon: Microcoleus vaginatus PCC 9802
Metabolites: urea (CHEBI:16199 · MediaIngredientMech · CMMMech)
Biological Processes:
- nitrogen fixation (GO:0009399 · PathwayMech)
- biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)
PARTIAL - Coculture-associated urea release and cyanobacterial low-concentration urea utilization provide a plausible, experimentally supported route for the nitrogen side of carbon-for-nitrogen trading. Coordinated expression supports Massilia-to-Microcoleus transfer, but exclusive donor attribution and the fraction of growth sustained by this route are not directly resolved.
Evidence
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doi:10.1093/ismejo/wrae246 - PARTIAL (IN_VITRO)"M. vaginatus and Massilia sp. METH4 in co-culture on N and C free media"
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doi:10.1093/ismejo/wrae246 - PARTIAL (IN_VITRO)"these results are consistent with the notion that urea is likely the vehicle for interspecies N transfer"
GABA and Glutamate Spatial Signaling
COLONIZATION_FACILITATIONGABA and glutamate released by C-limited Massilia sp. METH4 and N-starved M. vaginatus influence cyanobacterial motility and bundling. Addition experiments establish N-dependent chemokinetic and chemophobic responses, not measured Massilia migration; PCC 9802 did not show true chemotaxis to glutamate. Natural-bundle assays additionally measure gliding reversals, a response poorly retained in the long-cultured PCC 9802 strain. Low GABA can stabilize bundles, whereas high GABA can destabilize natural bundles, so increasing signal is not uniformly beneficial. The proposed benefit to carbon-for-nitrogen exchange is spatial retention near heterotrophic partners, not a directly measured flux increase.
Source Taxon: Massilia sp. METH4
Target Taxon: Microcoleus vaginatus PCC 9802
Metabolites: gamma-aminobutyric acid (CHEBI:16865 · MediaIngredientMech · CMMMech), L-glutamic acid (CHEBI:16015 · MediaIngredientMech · CMMMech)
Biological Processes:
- biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)
PARTIAL - GABA/glutamate responses keep nitrogen-limited Microcoleus trichomes bundled near cyanosphere partners, providing spatial proximity expected to facilitate nutrient exchange. Signal-addition and cyanosphere-cleansing experiments support bundle organization, but the increase in carbon-for-nitrogen flux or fitness attributable to this organization was not directly quantified. The responding motile organism is Microcoleus, not demonstrated recruitment of motile Massilia.
Evidence
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doi:10.1093/ismejo/wrad029 - SUPPORT (IN_VITRO)"the proximity of mutualistic diazotroph populations results in M. vaginatus bundle formation orchestrated through chemophobic and chemokinetic responses to gamma-aminobutyric acid (GABA) /glutamate (Glu) signals"
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doi:10.1093/ismejo/wrad029 - SUPPORT (IN_VITRO)"Glutamate, by contrast, was only produced in measurable quantities by M. vaginatus PCC 9802 and Massilia sp. METH4"
Associated Datasets
| Dataset | Type | Repository | Accession |
|---|---|---|---|
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Carbon-for-nitrogen cyanosphere nutrient-exchange publication
Primary publication establishing selective in vitro carbon-for-nitrogen exchange between M. vaginatus and pedigreed cyanosphere diazotroph isolates. |
PHENOTYPE | OTHER | PMID:32968213 |
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Exact-composition publication - Microcoleus vaginatus PCC 9802 and Massilia sp. METH4 GABA/Glu signaling
Follow-up publication using the same exact pair while testing GABA/glutamate signaling and spatial organization of the cyanosphere mutualism. |
PHENOTYPE | OTHER | doi:10.1093/ismejo/wrad029 |
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Exact-composition publication - Microcoleus vaginatus PCC 9802 and Massilia sp. METH4 urea transfer
Follow-up publication using the same exact pair for urea-related genome, expression, physiology, and nitrogen-transfer assays. |
PHENOTYPE | OTHER | doi:10.1093/ismejo/wrae246 |
|
Biological soil crust cyanosphere context publication
Contextual publication describing the natural M. vaginatus cyanosphere and nitrogen-fixing enrichment around M. vaginatus bundles; not treated as an exact-composition coculture publication. |
AMPLICON_16S | OTHER | doi:10.1186/s40168-019-0661-2 |
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN How much nutrient exchange is mediated specifically by heterotrophic urea and GABA/Glu-dependent spatial retention?
Retain demonstrated mutualistic growth, urea pool/release changes, supplied-urea growth and signal-induced motility. The wrae246 Results explicitly does not absolutely resolve the urea donor in coculture; total biomass normalizes release. No selective transfer tracing or uc/ah enzyme-affinity characterization establishes an exclusive carrier. The wrad029 experiments distinguish PCC 9802 from natural bundles, chemokinesis/chemophobia from true glutamate chemotaxis, and concentration-dependent stabilization from high-GABA destabilization. Improved nutrient-flux efficiency is the mechanistic interpretation, not an independently quantified endpoint. No new self-loop is inferred from the proposed feedback model.
Attaches to: ecological_interactions#Urea-Mediated Nitrogen Transfer, ecological_interactions#GABA and Glutamate Spatial Signaling
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| carbon and nitrogen limitation | carbon-free and nitrogen-free BG11-based coculture condition | N/A |
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| urea availability | low micromolar urea range tested as nitrogen source and transfer vehicle | N/A |
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| phototrophic incubation | 23 C with white light and 14 h light/10 h dark cycle | N/A |
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Growth Media
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