A defined marine diatom-bacterium coculture pairing the centric diatom Thalassiosira weissflogii, currently represented in NCBI Taxonomy as Conticribra weissflogii, with the diatom-attaching heterotrophic bacterium Marinobacter adhaerens HP15. The system is used to study phycosphere attachment, transparent exopolymer particle formation, aggregate formation, and sinking-particle processes relevant to the marine biological carbon pump. Multiple publications use the same exact diatom-bacterium model, including studies of aggregation requirements, chemotaxis-mediated attachment, and temperature/pCO2 perturbations.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Thalassiosira weissflogii — ontology label: Conticribra weissflogii | NCBITaxon:1577725 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
CROSS_FEEDER
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N/A |
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| Marinobacter adhaerens HP15 | NCBITaxon:225937 · 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.
Condition-Dependent Diatom Aggregation
In the 2011 rolling-tank assay, active T. weissflogii cocultured with attaching bacteria including HP15 formed substantially more aggregates than axenic controls. This is a community aggregation outcome, not a universal bacterial requirement or a separate colonization interaction. The 2014 temperature/pCO2 experiment found no effect of HP15 on total aggregate volume. Inactivated cells in the 2011 Results aggregated much less, not uniformly zero; the inactivation treatment may also have altered exudates and surface properties, so it does not isolate photosynthesis as the sole mediator.
Participating Taxa: Thalassiosira weissflogii, Marinobacter adhaerens HP15
Biological Processes:
- biological process involved in interspecies interaction between organisms (GO:0044419 · PathwayMech)
Evidence
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PMID:20827289 - SUPPORT (IN_VITRO)"specific diatom-attaching bacteria were required for aggregation"
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PMID:20827289 - SUPPORT (IN_VITRO)"T. weissflogii did not aggregate in axenic culture"
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doi:10.4056/sigs.922139 - SUPPORT (IN_VITRO)"it showed specific attachment to diatom cells. In vitro it led to exopolymer formation and aggregation of these algal cells to form marine snow particles"
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PMID:25375640 - SUPPORT (IN_VITRO)"total aggregate volume was independent of the presence of M. adhaerens HP15"
Condition-Dependent TEP Formation
TEP formation and aggregation were associated with the diatom-HP15 model in earlier work. TEP is a measured community polymer outcome, not proof of directed feeding from the diatom to HP15. The 2014 study found no bacterial effect on total TEP generated; warmer treatments generated more TEP but less aggregation. The 2011 aggregate-free-water measurements and 2014 total-TEP measurements must not be treated as identical endpoints. Chitin-containing fibres in a SEM caption document physical association, not the identity of all TEP or a measured chitin-transfer flux.
Participating Taxa: Thalassiosira weissflogii, Marinobacter adhaerens HP15
Biological Processes:
- photosynthesis (GO:0015979 · PathwayMech)
- extracellular matrix organization (GO:0030198 · PathwayMech)
PARTIAL: TEP can provide an adhesive matrix enabling diatom aggregation, but the amount-aggregation relationship is condition dependent. The 2011 association is not a selective mediation test; the 2014 higher-TEP/lower-aggregation result rules out a universal monotonic effect, and polymer stickiness was not directly resolved.
Evidence
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PMID:22820333 - SUPPORT (IN_VITRO)"induce transparent exopolymeric particle and aggregate formation"
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PMID:20827289 - SUPPORT (IN_VITRO)"TEP formation and phytoplankton aggregation"
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doi:10.3354/meps09894 - PARTIAL (IN_VITRO)"a co-incubation sample containing the diatom Thalassiosira weissflogii (left) and Marinobacter adhaerens HP15 embedded in a network of chitincontaining fibres extruding from the diatom cell"
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PMID:25375640 - SUPPORT (IN_VITRO)"had no effect on the amount of TEP generated"
Chemotaxis-Mediated Attachment
Diatom homogenate or culture supernatant attracted HP15, and chemotaxis-associated mutants had a smaller attached bacterial fraction in coculture than wild type. These perturbations support HP15 chemotaxis/motility contributions to bacterial attachment to the diatom, not a demonstrated growth or colonization benefit to the diatom. Mutant biofilm impairment was assayed on abiotic surfaces and is distinct from diatom aggregation.
Source Taxon: Marinobacter adhaerens HP15
Target Taxon: Thalassiosira weissflogii
Biological Processes:
- chemotaxis (GO:0006935 · PathwayMech)
- biofilm formation (GO:0042710 · PathwayMech)
HYPOTHESIZED: chemotaxis-dependent attachment may enable the close association underlying the earlier HP15 aggregation phenotype. The reviewed chemotaxis abstract demonstrates reduced attachment, not selective mediation of the aggregation endpoint; aggregation effects cannot be assumed in every environmental treatment.
Evidence
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PMID:22820333 - SUPPORT (IN_VITRO)"chemotaxis might be important for the interaction of M. adhaerens with diatoms"
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PMID:22820333 - SUPPORT (IN_VITRO)"the fraction of bacteria attaching to the diatom decreased significantly for mutants"
Aggregate Sinking and Carbon Export Interpretation
The existing marine-snow model interpretation concerns measured aggregate sinking and possible carbon export, not ecological niche partitioning. In the 2011 assay, aggregate size predicted sinking velocity while bacterial presence did not change the size-sinking relationship. Warmer 2014 treatments had depressed aggregation and sinking, especially with acidification. A resulting reduction in ocean carbon sequestration is an extrapolation, not a measured field flux or a demonstrated universal HP15 benefit.
Participating Taxa: Thalassiosira weissflogii, Marinobacter adhaerens HP15
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:20827289 - PARTIAL (IN_VITRO)"may enhance the efficiency of the biological pump"
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PMID:25375640 - PARTIAL (IN_VITRO)"potentially reduced carbon sequestration after diatom blooms"
Associated Datasets
| Dataset | Type | Repository | Accession |
|---|---|---|---|
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Exact-composition publication - diatom aggregation requirement
Primary study showing that photosynthetically active T. weissflogii and specific diatom-attaching bacteria, including HP15, were required for aggregation. |
PHENOTYPE | OTHER | PMID:20827289 |
|
Exact-composition publication - chemotaxis and attachment
Exact-system mechanistic study testing M. adhaerens chemotaxis and attachment to T. weissflogii cells and TEP aggregates. |
PHENOTYPE | OTHER | PMID:22820333 |
|
Exact-composition publication - future-ocean aggregation perturbation
Exact-system study of T. weissflogii aggregation and sedimentation with or without M. adhaerens HP15 under temperature and pCO2 scenarios. |
PHENOTYPE | OTHER | PMID:25375640 |
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN Which attachment and polymer properties causally control HP15-associated aggregation under each assay condition?
Mutant attachment, aggregate-free TEP, total TEP, aggregation and sinking are distinct measurements. Polymer chemistry/stickiness and exact mediation remain unresolved; the 2014 null bacterial effects and inverse temperature response constrain the earlier model. Full chemotaxis and MEPS bodies were not available for this review. Non-graph overstatements are tracked in #1884.
Attaches to: ecological_interactions#Condition-Dependent Diatom Aggregation, ecological_interactions#Condition-Dependent TEP Formation, ecological_interactions#Chemotaxis-Mediated Attachment, ecological_interactions#Aggregate Sinking and Carbon Export Interpretation
1 evidence item(s)
aggregation rates and sinking velocity of aggregates were depressed in warmer treatments
The abstract supplies a direct counterexample to universally increased aggregation with increased TEP.
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Photosynthetic activity | photosynthetically active versus inactivated diatom cells | N/A |
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| Temperature and pCO2 | two temperature and three pCO2 scenarios | N/A |
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