Defined synthetic bacterial coculture pairing phototrophic nitrogen-fixing Rhodopseudomonas palustris CGA676 with fermentative Escherichia coli PFM2 in an obligate bidirectional carbon-and-nitrogen cross-feeding relationship evolved for 650-800 generations alongside matched monocultures. Beyond engineered carbon (organic acids from glucose fermentation) and nitrogen (ammonium from N2 fixation) exchange, the coculture engages in additional cross-feeding of adenine and iron that represses biosynthesis and scavenging gene expression in the recipient and limits rather than promotes emergent metabolic dependencies.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
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| Rhodopseudomonas palustris CGA676 — ontology label: Rhodopseudomonas palustris | NCBITaxon:1076 · TaxonMech · TraitMech |
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PRIMARY_PRODUCER
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| Escherichia coli PFM2 — ontology label: Escherichia coli | NCBITaxon:562 · TaxonMech · TraitMech |
CROSS_FEEDER
PRIMARY_DEGRADER
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DOMINANT |
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Ecological Interactions
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Obligate Carbon and Nitrogen Cross-Feeding Between Escherichia coli and Rhodopseudomonas palustris
CROSS_FEEDINGIn anaerobic minimal medium containing glucose as the sole carbon source and N2 as the sole nitrogen source, fermentative Escherichia coli PFM2 supplies excreted organic acids to phototrophic Rhodopseudomonas palustris CGA676, while nitrogen-fixing R. palustris CGA676 excretes ammonium to support E. coli growth across 650-800 generations.
Source Taxon: Rhodopseudomonas palustris CGA676
Target Taxon: Escherichia coli PFM2
Metabolites: ammonium (CHEBI:28938 · MediaIngredientMech · CMMMech), organic acid (CHEBI:64709 · MediaIngredientMech · CMMMech)
Biological Processes:
- nitrogen fixation (GO:0009399 · PathwayMech)
- fermentation (GO:0006113 · PathwayMech)
DIRECTLY IMPLIED: Obligate carbon and nitrogen cross-feeding maintains stable coculture coexistence across 650-800 generations, enabling concurrent iron and adenine cross-feeding.
Evidence
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PMID:42117636 - SUPPORT (IN_VITRO)"Here, we compared mutations that were differentially enriched in bacterial monocultures versus cocultures pairing phototrophic Rhodopseudomonas palustris with fermentative Escherichia coli in an obligate cross-feeding relationship based on the exchange of nitrogen and carbon for 650-800 generations."
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PMID:42117636 - SUPPORT (IN_VITRO)"While coculture conditions required obligate exchange of nitrogen and carbon, additional cross-feeding of adenine and iron likely occurred."
Multilayered Iron and Adenine Cross-Feeding Repressing Recipient Gene Cost
CROSS_FEEDINGAlongside obligate carbon and nitrogen exchange, secondary cross-feeding of iron and purines (adenine) occurs in coculture across 650-800 generations.
Source Taxon: Rhodopseudomonas palustris CGA676
Target Taxon: Escherichia coli PFM2
Metabolites: iron cation (CHEBI:24875 · MediaIngredientMech · CMMMech), purines (CHEBI:26401 · MediaIngredientMech · CMMMech)
Biological Processes:
- iron ion transport (GO:0006826 · PathwayMech)
- regulation of gene expression (GO:0010468 · PathwayMech)
DIRECTLY IMPLIED: Iron and adenine cross-feeding represses expression of iron scavenging and adenine synthesis genes in the recipient, lowering gene cost and promoting gene retention.
Evidence
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PMID:42117636 - SUPPORT (IN_VITRO)"Contrary to expectations, the emergence of additional dependencies was observed in monoculture, but not in coculture, even though additional layers of cross-feeding involving iron and adenine were present in coculture."
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PMID:42117636 - SUPPORT (IN_VITRO)"We reasoned that iron and adenine cross-feeding occurred at levels sufficient to repress gene expression in the recipient, thereby promoting gene retention by lowering gene cost."
Repression of Iron Scavenging and Adenine Synthesis Gene Cost Promoting Gene Retention
CROSS_FEEDINGCross-feeding of iron and adenine represses expression of iron scavenging and adenine synthesis genes in cocultures while Escherichia coli acquires mutations suggestive of enhanced adenine uptake, lowering gene cost and limiting emergent metabolic dependencies.
Source Taxon: Escherichia coli PFM2
Target Taxon: Rhodopseudomonas palustris CGA676
Metabolites: iron cation (CHEBI:24875 · MediaIngredientMech · CMMMech), purines (CHEBI:26401 · MediaIngredientMech · CMMMech)
Biological Processes:
- regulation of gene expression (GO:0010468 · PathwayMech)
Evidence
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PMID:42117636 - SUPPORT (IN_VITRO)"Low expression of iron scavenging and adenine synthesis genes in cocultures suggested that cross-feeding repressed expression, thereby lowering gene cost."
Cross-Mech Suite Links
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