A defined marine algal-bacterial co-culture model between the coccolithophore Emiliania huxleyi CCMP3266 and the Roseobacter-group bacterium Phaeobacter inhibens DSM 17395. The interaction is dynamic: attached bacteria initially promote algal growth but later kill aging algal hosts. Evidence supports algal nutrient provisioning to the heterotrophic bacterium, bacterial attachment to naked algal cells, and indole-3-acetic acid production stimulated by algal-exuded tryptophan.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Emiliania huxleyi CCMP3266 — ontology label: Emiliania huxleyi | NCBITaxon:2903 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
CROSS_FEEDER
|
N/A |
|
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| Phaeobacter inhibens DSM 17395 | NCBITaxon:391619 · TaxonMech · TraitMech |
SYNTROPHIC_PARTNER
CROSS_FEEDER
|
N/A |
|
|||
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.
Algal Nutrient Provisioning Supports Bacterial Growth
CROSS_FEEDINGE. huxleyi CCMP3266 supports P. inhibens DSM 17395 growth in otherwise nonpermissive L1-Si medium. Nutrient-rescue comparisons support algal supply of usable nutrient forms; DMSP can contribute sulfur but did not alone provide an adequate carbon supply in the tested context. Bacterial growth was monitored as colony-forming units, which may represent rosettes rather than single cells. Nutrient support does not by itself demonstrate a causal step from general biomass increase to the specific tryptophan/IAA response.
Source Taxon: Emiliania huxleyi CCMP3266
Target Taxon: Phaeobacter inhibens DSM 17395
Evidence
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PMID:27855786 - SUPPORT (IN_VITRO)"E. huxleyi can provide all four essential nutrients"
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PMID:27855786 - SUPPORT (IN_VITRO)"CFU may include rosettes as well as individual bacteria"
Tryptophan-Enhanced Bacterial Attachment And IAA Production
Algal exudates supported tryptophan-auxotroph growth, establishing bioavailable tryptophan. In separate bacterial cultures, added tryptophan increased IAA production and isotope labeling demonstrated conversion of the added precursor into IAA. Added tryptophan also increased bacterial attachment in coculture, particularly to naked algal cells. These assays do not trace the complete endogenous algal-to-bacterial-to-algal flux or measure de novo tryptophan biosynthesis in the recipient. The E. coli auxotroph is an assay reporter, not a community member.
Source Taxon: Emiliania huxleyi CCMP3266
Target Taxon: Phaeobacter inhibens DSM 17395
Metabolites: tryptophan (CHEBI:16828 · MediaIngredientMech · CMMMech), indole-3-acetic acid (CHEBI:16411 · MediaIngredientMech · CMMMech)
HYPOTHESIZED: Tryptophan-enhanced IAA production could contribute to initial algal promotion and late killing. Added tryptophan accelerated coculture bleaching, but also changed attachment; bulk coculture IAA was undetectable and pathway mutants retained production. The experiment therefore does not isolate IAA mediation or show that measured bacterial IAA reached the exogenous toxic dose.
Evidence
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PMID:27855786 - SUPPORT (IN_VITRO)"Bacterial production of indole-3-acetic acid and attachment to algae are significantly increased by tryptophan"
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PMID:27855786 - SUPPORT (IN_VITRO)"all produced IAA is fully labeled"
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PMID:27855786 - SUPPORT (IN_VITRO)"This indicates that algal exudates contain bioavailable tryptophan"
Algal Growth Promotion and Late Killing with Proposed IAA Mediation
P. inhibens coculture initially increased algal yield, followed by late bleaching and increased algal death. Day-17 Sytox staining was reported as 94% dead in coculture versus 21% in axenic algae; day-20 TUNEL labeling showed more fragmented DNA. HYPOTHESIZED: IAA mediates both phases. Added IAA promoted growth at 1 and 100 micromolar but was harmful at 1000 micromolar; these are not measured coculture exposures. IAA was undetectable in coculture, and tested pathway mutants still produced IAA and bleached algae. The experiments do not establish IAA necessity, nutrient-consuming predation, a unique death pathway or natural-bloom termination.
Source Taxon: Phaeobacter inhibens DSM 17395
Target Taxon: Emiliania huxleyi CCMP3266
Metabolites: indole-3-acetic acid (CHEBI:16411 · MediaIngredientMech · CMMMech)
Evidence
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PMID:27855786 - PARTIAL (IN_VITRO)"Both algal growth enhancement and algal death are driven by the bacterially-produced phytohormone indole-3-acetic acid"
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PMID:27855786 - SUPPORT (IN_VITRO)"in these conditions IAA was undetectable"
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PMID:27855786 - SUPPORT (IN_VITRO)"these mutants were still capable of producing IAA"
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PMID:27855786 - SUPPORT (IN_VITRO)"while in the pure culture only 21% are dead by day 17"
Associated Datasets
| Dataset | Type | Repository | Accession |
|---|---|---|---|
|
Dynamic metabolic exchange article and figure data
Article-hosted culture, imaging, flow cytometry, metabolite, and gene-expression data describing the E. huxleyi-P. inhibens co-culture. |
PHENOTYPE | OTHER | eLife-17473 |
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Is endogenous IAA necessary for algal promotion and late killing in this coculture?
The main text explicitly hypothesizes IAA mediation despite categorical abstract wording. Bulk coculture IAA was undetectable, exogenous micromolar dose responses are not measured local exposure, and pathway mutants retained IAA and bleaching. Labeled precursor conversion in bacterial culture plus exudate auxotroph rescue does not trace the complete endogenous loop. Tryptophan addition is pleiotropic and changes attachment. Remove the nutrient-provisioning workflow arrow rather than infer a selective route. Roseobacticide activity against CCMP372 cannot be assigned to CCMP3266; neither that comparator nor the E. coli reporter is a community member. Death staining and expression associations do not uniquely establish a death pathway or global bloom effects. Preserve nonpermissive-medium guidance and original YAML aliases; non-graph claims remain #1456.
Attaches to: ecological_interactions#Algal Nutrient Provisioning Supports Bacterial Growth, ecological_interactions#Tryptophan-Enhanced Bacterial Attachment And IAA Production, ecological_interactions#Algal Growth Promotion and Late Killing with Proposed IAA Mediation
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| L1-Si seawater medium | Seawater-based L1 medium without silicate | N/A |
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| light-dark cycle | 12 h light / 12 h dark at 18 degrees Celsius | N/A |
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Growth Media
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