Assembly of the essential SpoIVA coat protein at the surface of developing bacterial spores
Abstract
Bacterial spores owe their remarkable resistance properties to a multilayered coat, one of the most resilient and durable biological structures on Earth. Assembled at the surface of the outer forespore membrane, the coat comprises dozens of proteins organized into distinct layers. Its formation is initiated by SpoIVA, which is proposed to form a polymeric scaffold for the innermost coat layer. Although SpoIVA has been shown to polymerize into filaments in vitro, there is currently no evidence demonstrating the formation of such assemblies in vivo, and the mechanism underlying its oligomerization remains unresolved. In this study, cryo-focused ion beam milling combined with cryo-electron tomography of sporulating Bacillus subtilis cells reveals that the SpoIVA layer consists of polymers that form track-like structures radiating from the mother cell-proximal forespore pole and extending directionally toward the distal pole. Subtomogram averaging further sheds light on their organized architecture, harboring a straight orientation, uniform spacing, and embedding in the outer forespore membrane. These observations also define SpoIVA spatial orientation relative to the outer forespore membrane. Furthermore, AlphaFold3 predictions, combined with biophysical and functional assays, show that SpoIVA dimerizes through its central and C-terminal regions. We further show that dimerization promotes SpoIVA localization around the forespore but is dispensable for polymer formation, which relies on the ATPase domain. Altogether, these findings suggest a dual oligomerization mechanism, in which SpoIVA transitions from dimers to linear track-like polymers, and reveal that these assemblies play critical roles in coat assembly and spore development.
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BibTeX
@misc{bauda2026assembly,
title = {{Assembly of the essential SpoIVA coat protein at the surface of developing bacterial spores}},
author = {Elda Bauda and Betty Fekade and Laure Bellard and Benoît Gallet and Séraphine Degroux and Emmanuelle Neumann and Caroline Mas and Kaitlyn Coleman and Aline Leroy and Grégory Effantin and Daphna Fenel and Jana Moravcova and Jiri Novacek and Christine Moriscot and Guy Schoehn and Christopher D.A. Rodrigues and Cécile Morlot},
howpublished = {HAL},
year = {2026},
month = oct,
doi = {10.64898/2026.07.09.737436},
url = {https://univ-grenoble-alpes.hal.science/hal-05798936v1},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Assembly of the essential SpoIVA coat protein at the surface of developing bacterial spores
AU - Elda Bauda
AU - Betty Fekade
AU - Laure Bellard
AU - Benoît Gallet
AU - Séraphine Degroux
AU - Emmanuelle Neumann
AU - Caroline Mas
AU - Kaitlyn Coleman
AU - Aline Leroy
AU - Grégory Effantin
AU - Daphna Fenel
AU - Jana Moravcova
AU - Jiri Novacek
AU - Christine Moriscot
AU - Guy Schoehn
AU - Christopher D.A. Rodrigues
AU - Cécile Morlot
PY - 2026
DA - 2026/10/16
PB - HAL
DO - 10.64898/2026.07.09.737436
UR - https://univ-grenoble-alpes.hal.science/hal-05798936v1
AB - Bacterial spores owe their remarkable resistance properties to a multilayered coat, one of the most resilient and durable biological structures on Earth. Assembled at the surface of the outer forespore membrane, the coat comprises dozens of proteins organized into distinct layers. Its formation is initiated by SpoIVA, which is proposed to form a polymeric scaffold for the innermost coat layer. Although SpoIVA has been shown to polymerize into filaments in vitro, there is currently no evidence demonstrating the formation of such assemblies in vivo, and the mechanism underlying its oligomerization remains unresolved. In this study, cryo-focused ion beam milling combined with cryo-electron tomography of sporulating Bacillus subtilis cells reveals that the SpoIVA layer consists of polymers that form track-like structures radiating from the mother cell-proximal forespore pole and extending directionally toward the distal pole. Subtomogram averaging further sheds light on their organized architecture, harboring a straight orientation, uniform spacing, and embedding in the outer forespore membrane. These observations also define SpoIVA spatial orientation relative to the outer forespore membrane. Furthermore, AlphaFold3 predictions, combined with biophysical and functional assays, show that SpoIVA dimerizes through its central and C-terminal regions. We further show that dimerization promotes SpoIVA localization around the forespore but is dispensable for polymer formation, which relies on the ATPase domain. Altogether, these findings suggest a dual oligomerization mechanism, in which SpoIVA transitions from dimers to linear track-like polymers, and reveal that these assemblies play critical roles in coat assembly and spore development.
ER -