TraitMech

TraitMech › MORPHOLOGY

spore shaped

METPO:1000682 · CLASS · REVIEWED

A cell shape in which an organism or differentiated cell has an endospore-like morphology, reflecting a dormant spore body with specialized protective layers.

Trait evidence (1)

  • DOI:10.1038/nrmicro2921
    structure of the endospore coat

    Supports endospore morphology as a differentiated structure with specialized surface layers.

Spore-shape endospore layer mechanism

Evidence-backed causal sketch linking spore-shaped morphology to forespore engulfment, cortex formation, coat assembly, and dehydrated spore-core maturation.

MECHANISTIC · Represents Bacillus endospore morphogenesis and coat assembly. The SpoIVA accession anchors one protein in the multiprotein coat program and does not stand in for SpoVM, SpoVID, CotE, or SafA.

Spore-shape endospore layer mechanism Interactive directed graph showing evidence-backed causal relationships for spore shaped.

Edge evidence

  • forespore engulfment establishes mature spore body

    Engulfment establishes the forespore as a distinct spore body.

  • cortex formation builds layer of mature spore body

    Cortex formation builds a specialized spore structural layer.

    • DOI:10.1038/nrmicro2921 spore surface layers Supports specialized spore layers as components of mature morphology.
  • coat assembly builds layer of mature spore body

    Coat assembly builds the multilayered external spore structure.

  • dehydrated spore core contributes to mature spore body RO:0002326

    Core dehydration contributes to mature spore architecture and resistance.

  • mature spore body manifests as spore shaped METPO:2007400

    Mature spore-body architecture manifests the spore-shaped trait.

  • Spo0A phosphorylation positively regulates sporulation initiation RO:0002213

    Phosphorylation of the master regulator Spo0A initiates sporulation.

    • DOI:10.1126/sciadv.adq0791 Spo0A is the master regulator governing entry into sporulation; sporulation initiates upon phosphorylation of Spo0A (generalized across endospore formers).
  • starvation positively regulates sporulation initiation RO:0002213

    Starvation triggers entry into the sporulation differentiation program.

  • sporulation initiation leads to forespore engulfment

    Sporulation initiation leads to forespore engulfment.

  • SpoIVA anchors spore coat

    SpoIVA anchors/tethers coat material to the spore surface (outer forespore membrane).

    • DOI:10.1038/nrmicro2921 SpoIVA functions to anchor coat material to the spore surface; required to tether the coat to the outer forespore membrane (conserved role).
  • SpoVM required for spore encasement

    SpoVM is required for the morphological transition that encases the forespore.

    • DOI:10.1038/nrmicro2921 SpoVM and SpoVID are required for the morphological transition from a single scaffold cap to a full spherical shell that encases the forespore.
  • SpoVID required for spore encasement

    SpoVID is required for spore encasement; mutants block formation of a full coat shell.

    • DOI:10.1038/nrmicro2921 SpoVID is explicitly required for spore encasement; spoVID mutants block formation of a full coat shell.
  • CotE required for assembly of outer coat

    CotE is required for assembly of the spore outer coat.

  • SafA required for assembly of inner coat

    SafA is required for assembly of the spore inner coat.

    • DOI:10.1038/nrmicro2921 SafA is necessary for inner coat assembly; SafA and CotE are respectively required for the deposition of the inner and outer coat.
  • spore encasement contributes to mature spore body RO:0002326

    Encasement changes the coat scaffold into the complete shell of the mature spore body.

    • DOI:10.1038/nrmicro2921 SpoVM and SpoVID are crucial for the transition from a single cap to a full spherical shell that encases the spore Verified against the public PMC author-manuscript full text.
  • outer coat part of spore coat biolink:part_of

    The outer coat is a structural layer of the spore coat.

    • DOI:10.1038/nrmicro2921 Three layers of the B. subtilis spore coat are observed in thin-section electron microscopy: a lamellar inner coat, a more coarsely layered outer coat and a recently identified layer named the crust Verified against the public PMC author-manuscript full text.
  • inner coat part of spore coat biolink:part_of

    The inner coat is a structural layer of the spore coat.

    • DOI:10.1038/nrmicro2921 The core is protected by the cortex (green) and the spore coat, which consists of four layers Verified against the public PMC author-manuscript full text.
  • spore coat part of mature spore body biolink:part_of

    The spore coat forms a shell attached around the mature forespore.

    • DOI:10.1038/nrmicro2921 the coat did not form a shell of protein around the forespore and was often found detached from the forespore surface Verified against the public PMC author manuscript; mutant failure defines the normal coat-shell attachment represented by this edge.

Protein and taxon examples

Graph nodeProteinTaxonUniProt statusRole and evidence
SpoIVA UniProtKB:P35149
Stage IV sporulation protein A (spoIVA) 		Bacillus subtilis 168
NCBITaxon:224308 		REVIEWED
retrieved 2026-08-25 · entry v134 · sequence v1

SpoIVA hydrolyzes ATP and self-assembles into the basement layer that supports deposition of the Bacillus spore coat.

  • DOI:10.1016/j.molcel.2008.05.030 ATP-driven self-assembly of a morphogenetic protein The primary Bacillus subtilis study establishes SpoIVA ATPase-dependent coat deployment and self-assembly; UniProt verifies the reviewed 168 protein.

Provenance

Identifier source
METPO (2026-06-12)
Author
Anthea Guo
Definition source
DOI:10.1038/nrmicro2921

Parent traits (1)

Synonyms (1)

  • spore-shaped RELATED_SYNONYM · metpo.owl

kg-microbe context

Matched 1 kg-microbe node via direct_metpo.

  • METPO:1000682 [-1.729, -2.644, -1.494, +0.751, …]

512-dim DeepWalkSkipGramEnsmallen embedding from kg-microbe (2026-04-25).

Nearest neighbors in embedding space

Top-8 cosine-similar METPO traits from the 2026-04-25 deepwalk (512-D).

Deep research

Generated by just research-trait; source: research/traits/morphology/spore_shaped-deep-research-falcon.md

Unreviewed literature output — not curated TraitMech content Ontology identifiers suggested below have not been resolved against their ontologies, and some are known to be wrong. Check any CURIE against the source before using it. 
# Curation-focused research report: **spore shaped**

## 1. Scope and recommended interpretation

**Trait:** spore shaped
**Identifier:** **METPO:1000682**
**Category:** MORPHOLOGY
**Term kind:** CLASS
**Parent:** METPO:1000666
**Synonym:** spore-shaped

### Scope summary

For TraitMech, **METPO:1000682** should denote the morphology of a differentiated bacterial **endospore-like cell body**, not merely the genetic capacity to sporulate. The canonical phenotype is an ovoid or ellipsoidal, metabolically dormant body containing a partially dehydrated core and genome, surrounded by an inner membrane, germ-cell-wall peptidoglycan, a thick cortex, an outer membrane, and a proteinaceous coat; some taxa additionally possess a crust or exosporium. This architecture is produced through polar septation, chromosome transfer, engulfment, cortex synthesis, coat encasement, maturation, and mother-cell lysis (khanna2020shapinganendospore pages 1-2, mckenney2013thebacillussubtilis pages 2-4, khanna2020shapinganendospore pages 2-4).

A useful graph endpoint is therefore:

> **mature layered endospore architecture —realizes→ METPO:1000682**

The morphology is related to—but should not be equated with—heat resistance, lysozyme resistance, dormancy, germination ability, phase brightness, or sporulation frequency. These are correlated physiological or assay traits. For example, *Clostridium sporogenes* `spoIVA` mutants generated immature and heteromorphic bodies with defective cortex, coat, and exosporium and failed to acquire normal resistance, demonstrating that resistance and morphology may fail together without being identical phenotypes (kuwana2024spoivaisan pages 1-2, kuwana2024spoivaisan pages 8-9).

### Boundary cases

**Include:**
- Mature free bacterial endospores with the characteristic layered dormant-cell body.
- Developing forespores only when an assay explicitly scores progression toward or disruption of this morphology.
- Taxon-specific surface variants—coat plus crust or coat plus exosporium—provided that the central endospore architecture is present.

**Exclude or model separately:**
- The general capacity to form spores: **GO:0030435**, “sporulation resulting in formation of a cellular spore,” is a biological process, not the morphology itself.
- Vegetative rod, coccoid, filamentous, or swollen-cell morphology.
- Fungal spores, actinomycete exospores/conidia, myxospores, cysts, and reproductive spores not formed by bacterial endosporulation.
- Phase-bright objects without structural confirmation; debris and storage granules can confound light-microscopy scoring.
- Resistance-only measurements. Heat- or lysozyme-resistant CFU provide useful maturation evidence but do not directly establish shape.
- Abnormal swirl structures, cortex-free immature spores, and mother-cell protein aggregates; these are negative or aberrant morphogenesis phenotypes rather than positive instances of **METPO:1000682** (kuwana2024spoivaisan pages 8-9).

## 2. Current mechanistic understanding

The best-resolved model is *Bacillus subtilis*. Polar septation creates a small forespore and a larger mother cell. Because only approximately one-third of the chromosome is initially trapped in the forespore, SpoIIIE transfers the remainder across the septum. The mother-cell membrane then migrates around the forespore in a phagocytosis-like engulfment event. After engulfment, cortex peptidoglycan is deposited between the two forespore membranes, while mother-cell proteins assemble a multilayered coat around the outer forespore membrane (khanna2020shapinganendospore pages 2-4).

Direct cryo-electron tomography showed that engulfment involves 10–30-nm-wide, 5–20-nm-long membrane projections. The process lasts approximately 60 minutes, increases mother-cell membrane area by about 2 µm² or 25%, and remodels the forespore from hemispherical toward ovoid while approximately doubling its size. Loss of any SpoIID–SpoIIM–SpoIIP component blocks membrane migration after polar septation; inhibition of new peptidoglycan synthesis also reduces or eliminates the projections. These experiments support a model in which newly synthesized peptidoglycan ahead of the leading edge is tethered and cleaved by the SpoIIDMP machinery, enabling membrane advance (khanna2019themoleculararchitecture pages 10-12, khanna2020shapinganendospore pages 9-11, khanna2019themoleculararchitecture pages 13-14, khanna2019themoleculararchitecture pages 4-5).

The cortex and coat then establish the mature boundary. The cortex is specialized peptidoglycan assembled between the inner and outer forespore membranes. The coat contains at least 70 proteins in *B. subtilis* and begins localizing during engulfment. Mature *B. subtilis* spores have inner coat, outer coat, and crust; other taxa may instead have an exosporium separated from the coat by an interspace (mckenney2013thebacillussubtilis pages 2-4).

## 3. Candidate graph nodes

### A. Trait and biological-process nodes

- **spore shaped** — **METPO:1000682**
- Parent morphology — **METPO:1000666**
- Sporulation resulting in formation of a cellular spore — **GO:0030435**
- Polar septation — label-only candidate pending exact ontology verification
- Chromosome translocation into forespore — label-only candidate
- Forespore engulfment — label-only candidate
- Cortex peptidoglycan biosynthesis — **GO:0009252** is a conservative generic grounding for peptidoglycan biosynthesis
- Coat assembly / spore encasement — label-only candidates
- Endospore maturation — label-only candidate
- Mother-cell lysis and spore release — label-only candidate

### B. Cellular structures and localizations

Showing the first 60 of 250 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.

Canonical examples (1)

Organisms cited as exemplars of this trait. Taxon ids are NCBITaxon and link out to the NCBI record.

Curation history

  1. · SEEDED_FROM_METPO · seed_from_metpo

    imported from data/raw/metpo.owl (CLASS)

  2. · CURATED_WITH_LITERATURE · codex

    Added DOI-backed definition and causal graph for forespore engulfment, cortex formation, coat assembly, dehydrated spore core, and mature spore-body morphology.

  3. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002326×1).

  4. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (METPO:2007400×1).

  5. · ENRICH_CAUSAL_GRAPH · claude

    Added 8 evidence-backed generic edges (12 new nodes) from the deep-research report.

  6. · GROUND_CAUSAL_NODES · claude

    Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:0031160×1).

  7. · GROUND_CAUSAL_NODES · claude

    Grounded 4 causal-node grounding field(s) via mappings/node_grounding.tsv (UniProtKB:A0A2K8N6W1×1, UniProtKB:A0A0B5ANC0×1, UniProtKB:D5WPR1×1, UniProtKB:A0A0N1QUA1×1).

  8. · RETRACT_DEAD_UNIPROT_GROUNDINGS · claude

    Retracted 1 UniProtKB grounding(s) whose accessions are deleted from UniProt; nodes demoted to label-only pending re-grounding (docs/GROUNDING_POLICY.md)

  9. · GROUND_CAUSAL_PREDICATES · claude

    Grounded 2 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002213×2).

  10. · REVIEW_UNIPROT_INSTANCE_GROUNDINGS · codex

    Reviewed 3 organism-specific UniProtKB grounding(s): replaced 2 with taxon-agnostic GO/InterPro terms and retracted 1 to label-only where no exact semantic term was supported (docs/GROUNDING_POLICY.md).

  11. · CURATE_PROTEIN_TAXON_EXAMPLE · claude

    Backfilled provenance (review issue 517) for the codex protein-taxon review tranche of 2026-08-24/25, which shipped without a per-record event. In this record the tranche: set graph scope spore_shaped_endospore_layers=MECHANISTIC with scope_notes; marked 2 GENE_OR_PROTEIN node(s) REVIEWED_LABEL_ONLY with grounding_notes (spovid_protein, safa_protein); added taxon-paired protein example(s) UniProtKB:P35149 on spoiva_protein (NCBITaxon:224308); regrounded 1 node(s) (spoiva_protein: none->InterPro:IPR014201); added canonical example(s) NCBITaxon:224308.

  12. · CONNECT_CAUSAL_GRAPH_COMPONENTS · codex

    Resolved issue #183 graph fragmentation (5 components to 1) using 4 source- and verbatim-snippet-backed connector(s). No paid research service was called.