A defined marine phototroph-heterotroph coculture in which the cyanobacterium Prochlorococcus marinus MIT9312 is paired with the heterotrophic helper bacterium Alteromonas macleodii EZ55. The system models an ocean-surface interaction where Prochlorococcus is vulnerable to hydrogen peroxide because it lacks catalase, while Alteromonas removes reactive oxygen species and thereby expands the conditions under which Prochlorococcus can grow. Elevated carbon dioxide perturbs this interaction by reducing Alteromonas catalase expression and hydrogen peroxide removal.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Prochlorococcus marinus MIT9312 — ontology label: Prochlorococcus marinus | NCBITaxon:1219 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
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N/A |
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| Alteromonas macleodii EZ55 — ontology label: Alteromonas macleodii | NCBITaxon:28108 · TaxonMech · TraitMech |
CROSS_FEEDER
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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.
Hydrogen Peroxide Cross-Protection
Alteromonas scavenging of hydrogen peroxide protects Prochlorococcus and supports growth under inhibitory peroxide and temperature conditions. Preserve this positive facilitation; it does not establish detoxification of every reactive oxygen species or a neutral fitness effect on Alteromonas.
Source Taxon: Alteromonas macleodii EZ55
Target Taxon: Prochlorococcus marinus MIT9312
Metabolites: hydrogen peroxide (CHEBI:16240 · MediaIngredientMech · CMMMech)
Biological Processes:
- response to oxidative stress (GO:0006979 · PathwayMech)
Hydrogen-peroxide removal reduces oxidative inhibition and permits helper-dependent Prochlorococcus growth. Retain this source-supported direction within the laboratory assay conditions, not as a universal requirement at every density or temperature.
Evidence
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PMID:29087377 - SUPPORT (IN_VITRO)"Alteromonas facilitate the growth of Prochlorococcus by scavenging HOOH"
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doi:10.1038/ismej.2017.189 - SUPPORT (IN_VITRO)"lacks the gene catalase and relies on 'helper' bacteria"
Carbon Dioxide Perturbation of Helper Function
At 800 versus 400 ppm CO2, cocultures showed reduced Alteromonas catalase transcripts, approximately sixfold lower peroxide removal and longer Prochlorococcus post-transfer lag with greater apparent die-off. PARTIAL: catalase-mediated weakening is the authors explanation; available evidence does not isolate catalase necessity from other CO2 responses.
Source Taxon: Alteromonas macleodii EZ55
Target Taxon: Prochlorococcus marinus MIT9312
Metabolites: carbon dioxide (CHEBI:16526 · MediaIngredientMech · CMMMech), hydrogen peroxide (CHEBI:16240 · MediaIngredientMech · CMMMech)
Biological Processes:
- response to oxidative stress (GO:0006979 · PathwayMech)
PARTIAL: reduced catalase expression is proposed to lower peroxide removal and weaken protection. Retain the measured treatment-associated loss of detoxification without treating transcript abundance as proof of the sole causal mediator.
Evidence
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doi:10.1038/ismej.2017.189 - SUPPORT (IN_VITRO)"decreased expression of the catalase gene"
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doi:10.1038/ismej.2017.189 - SUPPORT (IN_VITRO)"decrease in removal rates of hydrogen peroxide"
Helper-Dependent Prochlorococcus Growth
Helper coculture facilitates Prochlorococcus growth under the tested peroxide and thermal conditions at ecologically relevant concentrations. Preserve the positive growth response while keeping the separate temperature and CO2 experiments distinct.
Source Taxon: Alteromonas macleodii EZ55
Target Taxon: Prochlorococcus marinus MIT9312
Metabolites: hydrogen peroxide (CHEBI:16240 · MediaIngredientMech · CMMMech)
Biological Processes:
- response to oxidative stress (GO:0006979 · PathwayMech)
- growth (GO:0040007 · PathwayMech)
Evidence
-
PMID:29087377 - SUPPORT (IN_VITRO)"Alteromonas facilitate the growth of Prochlorococcus by scavenging HOOH"
Associated Datasets
| Dataset | Type | Repository | Accession |
|---|---|---|---|
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Prochlorococcus MIT9312 and Alteromonas EZ55 clone growth dataset
Growth experiment dataset for Prochlorococcus MIT9312 clones mixed with clonal isolates of Alteromonas EZ55 helper bacteria. |
PHENOTYPE | OTHER | BCO-DMO:688162 |
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN How much of the CO2 response is mediated specifically by helper catalase?
Peroxide protection remains supported and both existing directions remain. CO2-associated catalase transcription and peroxide-removal changes support a partial explanation, not exclusive mediation. Fresh abstracts were read; only introduction and early thermal methods were exposed by the public publisher archive before subsequent retrieval failures. No full-methods, supplement or figure-pixel verification is claimed. Exact strain and separate medium contexts remain #1722; missing access does not prove experiments are absent.
Attaches to: ecological_interactions#Hydrogen Peroxide Cross-Protection, ecological_interactions#Carbon Dioxide Perturbation of Helper Function, ecological_interactions#Helper-Dependent Prochlorococcus Growth
2 evidence item(s)
Alteromonas facilitate the growth of Prochlorococcus by scavenging HOOH
Directly supports the helper-bacterium peroxide-scavenging mechanism.
decreased expression of the catalase gene
Supports decreased catalase transcription, not a catalase-specific necessity or rescue experiment.
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Hydrogen peroxide stress | Ambient to elevated HOOH treatments | N/A |
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| Carbon dioxide | 400 ppm and 800 ppm | N/A |
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Growth Media
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