polyhydroxyalkanoate granule

GO:0070088 · Inclusion · Inclusion body · Proposed

A cytoplasmic prokaryotic inclusion body in which polyhydroxyalkanoate storage polymers condense with granule-associated proteins, including PHA synthases and phasins, to form hydrophobic carbon- and reducing-power storage granules. [DOI:10.1016/j.mcpro.2024.100765]

Synonyms: PHA granule; PHB granule

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
polyhydroxyalkanoate polymer core	Small molecule	part of	Reviewed label only (reviewed name; no accession asserted)		ESSENTIAL	Hydrophobic polyester storage material that forms the granule core and stores carbon plus reducing power. `DOI:10.1016/j.mcpro.2024.100765` Kelly et al. 2024 describe Pseudomonas putida PHA as a polymeric carbon-rich storage material sequestered in carbonosomes. `DOI:10.1038/srep26612` Bresan et al. 2016 analyzed isolated PHA granules and found PHA polymer plus protein, with no detectable phospholipid monolayer.
PHA synthases	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	phaC	ESSENTIAL	Granule-associated polymerase enzymes that synthesize PHA polyester and remain attached to nascent granules. `DOI:10.1128/JB.00779-12` Pfeiffer and Jendrossek 2012 localized PHB synthase PhaC1 to nascent and mature PHB granules in Cupriavidus necator H16. `DOI:10.1016/j.mcpro.2024.100765` Kelly et al. 2024 describe PHA synthases among the broad classes of PHA granule-associated proteins.
phasins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)		CONDITIONAL	Amphipathic granule-surface proteins that bind the PHA core and influence granule size, number and surface coverage. `DOI:10.1128/JB.00779-12` Pfeiffer and Jendrossek 2012 localized multiple Cupriavidus necator H16 phasins to PHB granules.

Taxonomic distribution

NCBITaxon:2 Bacteria — VARIABLE: PHA granules are bacterial intracellular inclusions whose production is distributed across heterotrophic, methylotrophic, and autotrophic producer strains. [DOI:10.3390/molecules29102293]

Canonical examples

NCBITaxon:381666 Cupriavidus necator H16 — PHB-accumulating model bacterium, historically Ralstonia eutropha H16, used to localize PhaC, phasins and PhaM during PHB granule formation. [DOI:10.1128/JB.00779-12]

Functions

carbon and reducing-power storage — PHA granules store excess carbon and reducing equivalents as intracellular polyester inclusions that can be mobilized when external nutrients become limiting.
- DOI:10.3390/molecules29102293 Fukala and Kucera 2024 review PHAs as intracellular biopolymers used by microorganisms for energy and carbon storage.

Mechanism graphs

PHA synthases and phasins build protein-coated PHA stores (ASSEMBLY)

PHA synthases produce the hydrophobic polyester core of a PHA granule, while phasins bind the granule surface and regulate surface coverage, granule number and granule size.

Subject	Predicate	Object	Evidence
PHA synthases	polymerize	polyhydroxyalkanoate polymer core	`DOI:10.3390/molecules29102293` Fukala and Kucera 2024 review the PHB synthesis pathway in which PhaA and PhaB form activated monomers that PhaC polymerizes into PHB.
polyhydroxyalkanoate polymer core	forms core of	polyhydroxyalkanoate granule	`DOI:10.1038/srep26612` Bresan et al. 2016 measured PHA polymer as the dominant chemical fraction of isolated PHA granules.
phasins	coat	polyhydroxyalkanoate granule	`DOI:10.1128/JB.00779-12` Pfeiffer and Jendrossek 2012 localized multiple phasins to PHB granules in Cupriavidus necator H16.
polyhydroxyalkanoate granule	stores	stored carbon and reducing power	`DOI:10.1016/j.mcpro.2024.100765` Kelly et al. 2024 describe Pseudomonas putida PHA as a polymeric carbon-rich storage material sequestered in carbonosomes.

Discussions

CURATION_TODO (RESOLVED): Should a phospholipid monolayer be curated as a PHA granule component? GO:0070088 still mentions a phospholipid monolayer from the older structural model, but Bresan et al. 2016 reported that purified PHA granules contain PHA and protein and no detectable phospholipids, so the monolayer is deliberately not curated as a component.
CURATION_TODO (OPEN): Resolve exact broad groundings for PHA polymer cores, PHA synthases and phasins. A curated ChEBI match was verified for poly(hydroxybutyrate), but the GO:0070088 record is broader than PHB; likewise, PHA synthase and phasin families are heterogeneous enough that exact family CURIEs need a separate InterPro/Pfam/NCBIfam pass.

Evidence

DOI:10.1016/j.mcpro.2024.100765 Kelly et al. 2024, Comprehensive Proteomics Analysis of Polyhydroxyalkanoate (PHA) Biology in Pseudomonas putida KT2440, Molecular & Cellular Proteomics.
DOI:10.3390/molecules29102293 Fukala and Kucera 2024, Natural Polyhydroxyalkanoates-An Overview of Bacterial Production Methods, Molecules.
DOI:10.1038/srep26612 Bresan et al. 2016, Polyhydroxyalkanoate (PHA) granules have no phospholipids, Scientific Reports.
DOI:10.1128/JB.00779-12 Pfeiffer and Jendrossek 2012, Localization of poly(3-hydroxybutyrate) granule-associated proteins during PHB granule formation in Cupriavidus necator H16, Journal of Bacteriology.
DOI:10.1186/1471-2180-12-262 Wahl et al. 2012, PHB granules are attached to the nucleoid via PhaM in Ralstonia eutropha, BMC Microbiology.

Curation history

2026-09-10T08:36:23Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-10T08:37:20Z claude · EXPANDED_RECORD — Added GO PHA/PHB synonymy, PHA polymer core, PHA synthase and phasin components, bacterial taxonomic scope, a Cupriavidus necator H16 canonical example, a carbon-storage function, record-level evidence, an assembly graph, a phospholipid-monolayer boundary decision and a grounding TODO.
2026-09-10T08:45:04Z claude · EDITED_RECORD — Moved the phospholipid-monolayer boundary discussion from a bare components section anchor to components#pha_polymer_core so the discussion target resolves to an existing local component anchor.
2026-09-10T08:51:42Z claude · EDITED_RECORD — Re-sourced the narrower PHB granule related synonym from GO:0070088 to a Cupriavidus necator H16 PHB-granule primary paper.
2026-09-21T18:44:05Z codex · REPLACED_UNREADABLE_EVIDENCE — #1257/#1259: Replaced unreadable Jendrossek 2009 citations with readable Fukala and Kucera 2024, Kelly 2024, Bresan 2016, and Pfeiffer and Jendrossek 2012 support.

Source: data/structures/inclusion/polyhydroxyalkanoate_granule.yaml