A hybrid photosynthetic microbiome that combines the engineered polyhydroxybutyrate-producing cyanobacterium Synechocystis sp. PCC 6803 PPT1 with the non-cyanobacterial fraction of a wild cyanobacteria-rich microbiome (WCRM). The engineered phototroph replaced the native cyanobacterial component of WCRM while retaining a heterotrophic community dominated by Proteobacteria/Pseudomonadota and Bacteroidota. PPHET accumulated up to 48% PHB per cell dry weight in nitrogen-limited small-scale photoautotrophic cultures, continued to accumulate PHB under dark acetate-fed conditions in which PHB granules localized primarily to heterotrophic members, and retained PHB production in non-sterile 4 L flat-panel and 8 L dark scaled reactors.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Synechocystis sp. PCC 6803 PPT1 — ontology label: Synechocystis sp. PCC 6803 | NCBITaxon:1148 · TaxonMech · TraitMech |
PRIMARY_PRODUCER
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DOMINANT |
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| non-cyanobacterial WCRM heterotrophs — ontology label: Bacteria | NCBITaxon:2 · 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.
Engineered Phototroph Integration
Synechocystis sp. PCC 6803 PPT1 was integrated into the retained non-cyanobacterial fraction of WCRM. Microscopy, plating, repeated propagation and colony PCR supported replacement and persistence of the engineered phototroph. PPHET preserved high PHB production comparable to axenic PPT1 and greater than WCRM. This is an experimental community-composition intervention and functional integration, not an isolated priority-effect or colonization-facilitation mechanism.
Biological Processes:
- photosynthesis (GO:0015979 · PathwayMech)
Replacing the native phototroph with PHB-optimized PPT1 gives the hybrid community high PHB-production capacity: PPHET reached 48% PHB/CDW, compared with 50% for axenic PPT1 and about 10% for WCRM under the matched small-scale regime. This supports the engineered phototroph contribution, not proof that every increment arises exclusively in PPT1 or from colonization facilitation.
Evidence
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PMID:41559821 - SUPPORT (IN_VITRO)"Microscopy analysis validated the successful colonisation and replacement of the original phototrophic strain with PPT1 or GFP"
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PMID:41559821 - SUPPORT (IN_VITRO)"PPHET reached similar PHB levels, up to 48% PHB/CDW"
Nitrate-Limited Photoautotrophic PHB Production
In the 19-day small-scale BG110 regime with 5 mM nitrate and 10 mM bicarbonate, followed by a 50 mM bicarbonate boost after nitrate depletion, PPHET reached up to 48% PHB/CDW versus 50% for PPT1 and about 10% for WCRM, with three biological replicates. HPLC measured bulk PHB; BODIPY-positive non-Synechocystis cells suggest additional producers but do not resolve each taxon or its PHB flux. These production phenotypes do not demonstrate reduced competition through niche partitioning.
Metabolites: hydrogencarbonate (CHEBI:17544 · MediaIngredientMech · CMMMech), nitrate (CHEBI:17632 · MediaIngredientMech · CMMMech), poly(3-hydroxybutyrate) (CHEBI:53389 · MediaIngredientMech · CMMMech)
Biological Processes:
- photosynthesis (GO:0015979 · PathwayMech)
Evidence
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PMID:41559821 - SUPPORT (IN_VITRO)"PPHET reached similar PHB levels, up to 48% PHB/CDW"
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PMID:41559821 - PARTIAL (IN_VITRO)"other members of the community stained positive for BODIPY"
Dark Acetate PHB Accumulation
After photoautotrophic growth, 30 mM acetate and 10 mM bicarbonate in BG110 supported further dark PHB accumulation in PPHET but not axenic PPT1. At two weeks, dark PPHET reached about 38% PHB/CDW but only about 23 mg/L, versus about 55% and 250 mg/L in light, reflecting different biomass. BODIPY granules localized primarily to non-cyanobacterial cells in darkness. This supports condition-dependent metabolic flexibility, not measured inter-member transfer or demonstrated competition-reducing niche separation.
Metabolites: acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), poly(3-hydroxybutyrate) (CHEBI:53389 · MediaIngredientMech · CMMMech)
Evidence
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PMID:41559821 - SUPPORT (IN_VITRO)"In darkness, only PPHET continued to accumulate PHB, reaching ~38% PHB/CDW"
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PMID:41559821 - SUPPORT (IN_VITRO)"PHB granules localised primarily in heterotrophic members of the community"
PPHET Stress Resilience and Scaled PHB Production
PPHET retained pigmentation, biomass and PHB under increased light and recovered from transient 38 C heat stress better than axenic PPT1. Small-scale high-light PHB averaged about 300 versus 100 mg/L; nonsterility alone had only a minor small-scale effect. In nonsterile scale-up, PPT1 collapsed after added illumination while PPHET kept growing. Separate PPHET production runs reached 33% PHB/CDW (about 250 mg/L) in a 4 L high-light flat panel and 22% (about 70 mg/L) in an 8 L non-aerated dark acetate reactor. These support community-associated resilience and production, not proven oxygen-scavenging mediation, anaerobiosis from lack of aeration, or equivalent yield across reactors.
Evidence
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PMID:41559821 - SUPPORT (IN_VITRO)"PPHET maintained pigmentation during heat stress and resumed growth upon return to standard conditions."
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PMID:41559821 - SUPPORT (IN_VITRO)"PPHET reached 33% PHB/CDW (~250 mg L−1)"
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PMID:41559821 - SUPPORT (IN_VITRO)"yielded 22% PHB/CDW (~70 mg L−1)"
Associated Datasets
| Dataset | Type | Repository | Accession |
|---|---|---|---|
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PPHET and WCRM 16S rRNA amplicon sequencing
European Nucleotide Archive deposition for the 16S rRNA amplicon data used to compare PPHET and WCRM community structure. |
AMPLICON_16S | ENA | PRJEB98235 |
Knowledge gaps & discussions (2)
EMERGING_HYPOTHESIS OPEN Do PPHET heterotrophs directly protect Synechocystis PPT1 by consuming photosynthetically produced oxygen and lowering reactive-oxygen stress, or does the stress tolerance come from another community function?
Zini et al. propose heterotrophic oxygen scavenging as a possible mechanism for high-light tolerance but report it as qualitative support rather than a direct pairwise mechanism, so the record tracks it as a hypothesis instead of an asserted interaction.
Attaches to: ecological_interactions#PPHET Stress Resilience and Scaled PHB Production
1 evidence item(s)
A possible explanation for this robustness is the presence of heterotrophic partners
Author-proposed oxygen-scavenging mechanism with qualitative observations, not an isolated mediator experiment. The full_text label is replaced by a documented provenance category.
KNOWLEDGE_GAP OPEN Which community functions mediate stress recovery and condition-specific PHB localization under matched conditions?
Preserve functional integration and its existing production arrow. High-light/heat manipulations support resilience; oxygen scavenging remains proposed. Community production does not itself establish colonization facilitation or competition-reducing niche partitioning. HPLC bulk PHB, qualitative cell localization, small-scale titers and separate scaled reactors must remain distinct. Prior dark/scale workflow arrows stay absent.
Attaches to: ecological_interactions#Engineered Phototroph Integration, ecological_interactions#Nitrate-Limited Photoautotrophic PHB Production, ecological_interactions#Dark Acetate PHB Accumulation, ecological_interactions#PPHET Stress Resilience and Scaled PHB Production
1 evidence item(s)
PPHET maintained pigmentation during heat stress and resumed growth upon return to standard conditions.
Positive recovery after heat stress; the mechanism is unresolved.
External Resources
| Name | Repository | Resource ID |
|---|---|---|
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Primary publication DOI
DOI landing page for the Microbial Biotechnology article that constructed and characterized the PPHET hybrid photosynthetic PHB microbiome. |
OTHER | doi:10.1111/1751-7915.70302 |
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Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| Nitrate limitation | 4-8 mM NaNO3 | N/A |
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| Light and temperature stress | elevated light and 38 C heat shock | N/A |
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Growth Media
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