Sleutel Mike, Sogues Adrià, Van Gerven Nani, Jonsmoen Unni Lise, Van Molle Inge, Fislage Marcus, Theunissen Laurent Dirk, Bellis Nathan F, Baquero Diana P, Egelman Edward H, Krupovic Mart, Wang Fengbin, Aspholm Marina, Remaut Han
Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium.
Structural and Molecular Microbiology, VIB-VUB Center for Structural Biology, Brussels, Belgium.
Nat Commun. 2025 Aug 16;16(1):7652. doi: 10.1038/s41467-025-62896-3.
For over 100 years, Bacillus thuringiensis (Bt) has been used as an agricultural biopesticide to control pests caused by insect species in the orders of Lepidoptera, Diptera, and Coleoptera. Under nutrient starvation, Bt cells differentiate into spores and associated toxin crystals that can adopt biofilm-like aggregates. We reveal that such Bt spore/toxin biofilms are embedded in a fibrous extrasporal matrix, and using cryoID, we resolved the structure and molecular identity of an uncharacterized type of pili, referred to here as Fibrillar ENdospore Appendages or F-ENA. F-ENA are monomolecular protein filaments anchored to the exosporium and tipped with a flexible fibrillum. Phylogenetic and structural analyses reveal that F-ENA are conserved in Bacilli and Clostridia, featuring head-neck domains with β-barrel necks that interlock via N-terminal hook peptides. In Bacillus, two collagen-like proteins (F-Anchor and F-BclA), respectively, tether F-ENA and form the distal tip. Sedimentation assays suggest F-ENA promotes spore clustering via F-BclA contacts and/or filament bundling.
100多年来，苏云金芽孢杆菌（Bt）一直被用作农业生物杀虫剂，以控制鳞翅目、双翅目和鞘翅目昆虫种类所引起的害虫。在营养饥饿条件下，Bt细胞分化为孢子和相关的毒素晶体，这些晶体可形成类似生物膜的聚集体。我们发现，这种Bt孢子/毒素生物膜嵌入在纤维状的芽孢外基质中，并且通过冷冻电镜断层成像技术（cryoID），我们解析了一种未被表征的菌毛类型的结构和分子特性，在此将其称为纤维状芽孢内附属物（Fibrillar ENdospore Appendages，F-ENA）。F-ENA是单分子蛋白丝，锚定在外孢子上，并带有一个柔性纤维。系统发育和结构分析表明，F-ENA在芽孢杆菌属和梭菌属中是保守的，其特征是具有通过N端钩状肽相互锁定的β桶状颈部的头颈部结构域。在芽孢杆菌中，两种胶原蛋白样蛋白（F-Anchor和F-BclA）分别束缚F-ENA并形成远端末端。沉降分析表明，F-ENA通过F-BclA接触和/或细丝捆绑促进孢子聚集。
