endospore external encapsulating structure

GO:0043591 · Spore · Envelope layer · Proposed

The layered envelope that surrounds a bacterial endospore and gives it its resistance: a thick modified peptidoglycan cortex, a proteinaceous coat of dozens of proteins outside it, and in some species an additional loose exosporium. It encases the dehydrated, mineralised core in which the chromosome is held. [GO:0043591]

Synonyms: spore coat and cortex

Has part: endospore coat (GO:0043593); endospore cortex (GO:0043595); outer endospore membrane (GO:0043594)

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
endospore cortex peptidoglycan	Peptidoglycan	part of				ESSENTIAL	A thick, chemically modified peptidoglycan layer whose muramic-δ-lactam residues make it a substrate for germination-specific lytic enzymes; it holds the core dehydrated. `DOI:10.1128/9781555819323.ch10` Spore Resistance Properties (2016) attributes core dehydration and heat resistance to the cortex.
endospore coat proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	cotE, spoIVA, safA	over 70 distinct proteins in Bacillus subtilis	ESSENTIAL	Self-assembling multilayered protein shell that excludes lytic enzymes and large toxic molecules, built on the SpoIVA basement layer with CotE and SafA as morphogenetic organisers. `DOI:10.1038/nrmicro2921` McKenney et al. 2012 describe the coat's layers and the morphogenetic proteins that organise them.
exosporium	Protein	part of		bclA		DISPENSABLE	A loose outermost balloon-like layer present in some species and absent in Bacillus subtilis; it carries the spore's outward-facing surface. `DOI:10.1038/nrmicro2921` McKenney et al. 2012 contrast species with an exosporium against B. subtilis, which lacks one.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

endospore coat proteins

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P14016`	Spore coat morphogenetic protein CotE	cotE	Bacillus subtilis subsp. subtilis str. 168 (`NCBITaxon:224308`)	REVIEWED
Role and evidence (2 references) Exact ePSORTdb experimental canary: P14016 is assigned to Spore outer coat; current protein identity and taxon were independently verified in UniProtKB. `https://db.psort.org/search/results?dataset=e&refseq=P14016&show_adjust=1` The exact ePSORTdb result links P14016 (Spore coat protein E) from taxon 224308 to secondary localization 'Spore outer coat' and PMID:3139490. `PMID:3139490` Zheng et al. identify CotE as a morphogenetic protein required to assemble the outer Bacillus subtilis endospore coat.
`UniProtKB:P35149`	Stage IV sporulation protein A	spoIVA	Bacillus subtilis subsp. subtilis str. 168 (`NCBITaxon:224308`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene spoIVA in Bacillus subtilis subsp. subtilis str. 168, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `https://www.uniprot.org/uniprotkb/P35149` UniProtKB reviewed (Swiss-Prot) entry P35149, the single reviewed entry for gene spoIVA in Bacillus subtilis subsp. subtilis str. 168. Establishes the accession and gene identity only; the component's membership in this structure rests on the record's own sources.
`UniProtKB:O32062`	Spore coat morphogenetic protein SafA	safA	Bacillus subtilis subsp. subtilis str. 168 (`NCBITaxon:224308`)	REVIEWED
Role and evidence (3 references) The single reviewed UniProtKB entry for gene safA in Bacillus subtilis subsp. subtilis str. 168, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `PMID:11325931` Ozin AJ et al. 2001, ‘SpoVID guides SafA to the spore coat in Bacillus subtilis.’, J Bacteriol. ECO:0000269 experimental evidence cited by UniProt for the 'Forespore' localisation of O32062. `PMID:30168214` Nunes F et al. 2018, ‘SpoVID functions as a non-competitive hub that connects the modules for assembly of the inner and outer spore coat layers in Bacillus subtilis.’, Mol Microbiol. ECO:0000269 experimental evidence cited by UniProt for the 'Forespore' localisation of O32062. `PMID:30455281` Pereira FC et al. 2019, ‘A LysM Domain Intervenes in Sequential Protein-Protein and Protein-Peptidoglycan Interactions Important for Spore Coat Assembly in Bacillus subtilis.’, J Bacteriol. ECO:0000269 experimental evidence cited by UniProt for the 'Forespore' localisation of O32062.

Taxonomic distribution

NCBITaxon:1239 Bacillota — COMMON: Endospore formation is essentially confined to this phylum, and lost in many lineages within it. [DOI:10.1038/nrmicro2921]
NCBITaxon:2157 Archaea — ABSENT [DOI:10.1038/nrmicro2921]

Canonical examples

NCBITaxon:1423 Bacillus subtilis — The model system for coat assembly and sporulation genetics. [DOI:10.1038/nrmicro2921]
NCBITaxon:224308 Bacillus subtilis subsp. subtilis str. 168 — Experimental reference strain for CotE-dependent outer spore-coat assembly. [PMID:3139490]

Functions

spore-mediated resistance to environmental stress — The cortex dehydrates the core and the coat excludes lytic enzymes and chemicals, giving decades of dormancy and resistance to heat, radiation and solvents.
- DOI:10.1128/9781555819323.ch10 Spore Resistance Properties (2016) reviews the contributions of cortex and coat to resistance.
- DOI:10.1038/nrmicro2921 McKenney et al. 2012 describe the coat as a barrier to lytic enzymes and toxic chemicals.

Associated traits

REQUIRED_FOR METPO:1000870 sporulation
- DOI:10.1038/nrmicro2921 McKenney et al. 2012 describe coat and cortex assembly as stages of sporulation; TraitMech records the phenotype as METPO:1000870.

Mechanism graphs

SpoIVA and CotE organize spore coat layer assembly (ASSEMBLY)

SpoIVA self-assembly creates the basement scaffold that anchors early coat morphogenesis around the forespore. CotE then localizes outside that inner scaffold and organizes assembly of the outer Bacillus subtilis spore coat.

Subject	Predicate	Object	Evidence
SpoIVA	self-assembles into	spore coat basement layer	`DOI:10.1016/j.molcel.2008.05.030` Ramamurthi and Losick 2008 reconstituted ATP-driven SpoIVA self-assembly into cable-like higher-order structures.
spore coat basement layer	recruits	inner spore coat	`DOI:10.1101/gad.8.2.234` Driks et al. 1994 localized key coat proteins and proposed that SpoIVA creates the basement layer used for coat assembly.
inner spore coat	positions	CotE	`DOI:10.1038/nrmicro2921` McKenney, Driks and Eichenberger 2012 review CotE as a morphogenetic organizer assembled outside the inner coat.
CotE	organizes	outer spore coat	`PMID:3139490` Zheng et al. identified CotE as a morphogenetic protein required for outer Bacillus subtilis coat assembly.
outer spore coat	layers with	endospore coat	`DOI:10.1038/nrmicro2921` McKenney, Driks and Eichenberger 2012 review the basement, inner, outer and crust layers that make up the Bacillus subtilis spore coat.

Cortex dehydration and coat barriers make spores stress resistant (FUNCTION)

The chemically modified cortex is the peptidoglycan layer that maintains a dehydrated spore core, and dehydration is a major source of wet-heat resistance. Outside the cortex, morphogenetic coat proteins assemble dozens of proteins into a multilayered shell that blocks lytic enzymes and large toxic molecules.

Subject	Predicate	Object	Evidence
endospore cortex	maintains	dehydrated spore core	`DOI:10.1128/9781555819323.ch10` Setlow 2016 reviews the cortex contribution to spore core dehydration and wet-heat resistance.
dehydrated spore core	enables	spore-mediated stress resistance	`DOI:10.1128/9781555819323.ch10` Setlow 2016 reviews low core water content as a determinant of spore wet-heat resistance.
endospore coat proteins	assembles into	endospore coat	`DOI:10.1038/nrmicro2921` McKenney, Driks and Eichenberger 2012 review the morphogenetic hierarchy that builds Bacillus subtilis spore coat layers. `PMID:3139490` Zheng et al. identified CotE as a morphogenetic protein required for outer Bacillus subtilis coat assembly.
endospore coat	forms	endospore external encapsulating structure	`DOI:10.1038/nrmicro2921` McKenney, Driks and Eichenberger 2012 review the spore coat as a multilayered shell outside the cortex.
endospore coat	excludes	enzyme and toxin barrier	`DOI:10.1038/nrmicro2921` McKenney, Driks and Eichenberger 2012 describe the coat as a barrier against lytic enzymes and large toxic molecules.
enzyme and toxin barrier	contributes to	spore-mediated stress resistance	`DOI:10.1128/9781555819323.ch10` Setlow 2016 reviews spore resistance properties contributed by external endospore structures.

Evidence

DOI:10.1038/nrmicro2921 McKenney PT, Driks A, Eichenberger P 2012, 'The Bacillus subtilis endospore: assembly and functions of the multilayered coat', Nature Reviews Microbiology.
DOI:10.1128/9781555819323.ch10 'Spore Resistance Properties', in The Bacterial Spore (2016).

Curation history

2026-09-01T03:41:49Z claude · CREATED_RECORD — Drafted from the cited reviews; every GO term, taxon id and DOI resolved live before writing. Not yet human-reviewed.
2026-09-02T22:22:21Z psortdb · SEED_PROTEIN_EXAMPLE — Added exact ePSORTdb experimental P14016/CotE spore-outer-coat example with PMID:3139490; validated the pinned WebArchive-wrapped v4 artifact, then independently verified reviewed protein identity, gene and strain taxon at UniProtKB and the PMID at NCBI. Source licensing responsibility was accepted by the maintainer; no cPSORTdb predictions or bulk prose were stored.
2026-09-04T01:21:41Z codex · ADD_CAUSAL_GRAPH — Added a FUNCTION graph linking cortex-dependent core dehydration and multilayer coat assembly to spore resistance.
2026-09-04T03:59:00Z codex · ADD_CAUSAL_GRAPH — Added a SpoIVA/CotE ASSEMBLY graph for Bacillus subtilis spore coat morphogenesis, grounded cortex and coat nodes to their exact GO part terms, and added primary evidence for SpoIVA-driven basement-layer assembly.
2026-09-08T07:40:30Z uniprot_genes · SEED_PROTEIN_EXAMPLES — #183: added 2 protein example(s) by resolving each of the component's declared gene symbols to the single reviewed UniProtKB entry for that symbol in a taxon this record names, deduplicated by accession. Symbols resolving to more than one reviewed entry were skipped rather than chosen between.
2026-09-20T21:51:50Z codex · ADDRESSED_REVIEW — Removed the endospore cortex graph node's component_ref so the GO:0043595 structure node no longer points at the narrower peptidoglycan component.

Source: data/structures/spore/endospore_external_encapsulating_structure.yaml