A defined synthetic coculture pairing the type II methanotroph Methylocystis parvus with the heterotrophic bacterium Rhodococcus opacus for methane-linked polyhydroxyalkanoate production. The coculture was first evaluated for methane-to-poly(3-hydroxybutyrate) conversion and then used in a two-stage PHBV accumulation strategy with nutrient starvation, methane, oxygen or air, valeric acid, and a volatile fatty acid mixture containing acetic, propionic, butyric, and valeric acids. The system is relevant to methane valorization, waste-derived volatile fatty acid upgrading, and biopolymer production.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
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| Methylocystis parvus | NCBITaxon:134 · TaxonMech · TraitMech |
PRIMARY_DEGRADER
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ABUNDANT |
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| Rhodococcus opacus | NCBITaxon:37919 · TaxonMech · TraitMech |
CROSS_FEEDER
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ABUNDANT |
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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.
Valeric-Acid PHBV Accumulation
After methane growth, the defined M. parvus OBBP/R. opacus DSM 43205 coculture was transferred to nitrogen-free medium at pH 7 with externally supplied valeric acid (30% of total carbon). PHBV accumulated under both air and CH4:O2 headspaces: maxima were 35.9 +/- 8.6% and 68 +/- 7% by mass, respectively. These are whole-coculture polymer contents, not reciprocal benefit or measured VFA exchange. A separate Methylocystis-enriched community is a comparator, not an additional member; under air it produced PHV without PHB, unlike the defined pair.
Participating Taxa: Methylocystis parvus, Rhodococcus opacus
Metabolites: valeric acid (CHEBI:17418 · MediaIngredientMech · CMMMech)
Evidence
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PMID:38516398 - SUPPORT (IN_VITRO)"valeric acid promoted PHBV accumulation in both cultures regardless of the atmosphere"
Mixed-VFA PHBV Accumulation Under Tested Gas Conditions
The methane-grown defined coculture received a synthetic acetate/propionate/butyrate/valerate mixture (15% of total carbon) in nitrogen-free medium, not actual waste effluent. PHBV accumulated with CH4:O2 (33.3:66.6) but was not detected under air. Because oxygen supply also differs, this is a positive gas-condition contrast, not an oxygen-matched selective methane test. Peak coculture PHBV content was 73.7 +/- 2.5% by mass on day 18 (PHB:PHV 94:6), versus 49.6 +/- 13% in the separately tested mixed consortium. Polymer fraction is not biomass yield, partner-resolved synthesis or proof of mutualism; bulk measurements do not isolate R. opacus mediation.
Participating Taxa: Methylocystis parvus, Rhodococcus opacus
Metabolites: methane (CHEBI:16183 · MediaIngredientMech · CMMMech), acetate (CHEBI:30089 · MediaIngredientMech · CMMMech), propionate (CHEBI:17272 · MediaIngredientMech · CMMMech), butyrate (CHEBI:17968 · MediaIngredientMech · CMMMech), valeric acid (CHEBI:17418 · MediaIngredientMech · CMMMech)
Evidence
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PMID:38516398 - SUPPORT (IN_VITRO)"VFAs mixture containing acetic, propionic, butyric, and valeric acids"
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PMID:38516398 - SUPPORT (IN_VITRO)"mixture of VFAs supported PHBV accumulation"
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PMID:38516398 - SUPPORT (IN_VITRO)"only in the presence of methane"
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PMID:38516398 - SUPPORT (IN_VITRO)"The highest PHBV contents for the coculture and the mixed consortium"
Knowledge gaps & discussions (1)
KNOWLEDGE_GAP OPEN What does Rhodococcus contribute to PHBV accumulation under oxygen-matched conditions?
Remove two design/stage nodes and three workflow arrows; merge the peak node into its mixed-VFA endpoint and remove the duplicate arrow. Preserve positive PHBV contents and distinguish the separate mixed consortium, PHV-only air result, supplied VFAs and synthetic feed. The current paper compares cultures and literature, not a matched pure-M. parvus removal/addback test for every PHBV condition. Proposed byproduct scavenging is not directly measured here. Main text/captions and Tables 1-2 read; original images, raw data and the earlier exact-pair paper were not audited. #1605 repairs graph scope; metadata, PHB mapping and canonical taxonomy remain #1606.
Attaches to: ecological_interactions#Valeric-Acid PHBV Accumulation, ecological_interactions#Mixed-VFA PHBV Accumulation Under Tested Gas Conditions
External Resources
| Name | Repository | Resource ID |
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Exact-system PHBV primary publication
Primary 2024 publication reporting M. parvus and R. opacus cocultivation for PHBV accumulation from methane and volatile fatty acid cosubstrates. |
OTHER | PMID:38516398 |
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Exact-system DOI landing page
DOI for the ACS Sustainable Chemistry and Engineering PHBV coculture study. |
OTHER | doi:10.1021/acssuschemeng.3c08570 |
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Earlier exact-species methane-to-PHB coculture publication
Earlier Chemical Engineering Journal study that included the same exact Methylocystis parvus and Rhodococcus opacus species-pair composition for methane-to-PHB conversion, before the PHBV/VFA follow-up. |
OTHER | doi:10.1016/j.cej.2023.146646 |
Environmental Factors
| Factor | Value | Unit |
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| Methane and oxygen headspace | CH4:O2 headspace or air | N/A |
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| VFA cosubstrate composition | valeric acid or mixed acetate, propionate, butyrate, and valeric acid | N/A |
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| Nutrient starvation and pH control | nitrogen-free medium with pH adjusted to 7 | N/A |
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Growth Media
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