Univ. Grenoble Alpes, CNRS, CEA, IBS, F-38000, Grenoble, France.
CEITEC-Central European Institute of Technology, Masaryk University, 62500, Brno, Czech Republic.
Nat Commun. 2024 Feb 14;15(1):1376. doi: 10.1038/s41467-024-45770-6.
Bacterial spores owe their incredible resistance capacities to molecular structures that protect the cell content from external aggressions. Among the determinants of resistance are the quaternary structure of the chromosome and an extracellular shell made of proteinaceous layers (the coat), the assembly of which remains poorly understood. Here, in situ cryo-electron tomography on lamellae generated by cryo-focused ion beam micromachining provides insights into the ultrastructural organization of Bacillus subtilis sporangia. The reconstructed tomograms reveal that early during sporulation, the chromosome in the forespore adopts a toroidal structure harboring 5.5-nm thick fibers. At the same stage, coat proteins at the surface of the forespore form a stack of amorphous or structured layers with distinct electron density, dimensions and organization. By analyzing mutant strains using cryo-electron tomography and transmission electron microscopy on resin sections, we distinguish seven nascent coat regions with different molecular properties, and propose a model for the contribution of coat morphogenetic proteins.
细菌孢子之所以具有令人难以置信的抗逆能力，是因为其分子结构能够保护细胞内容物免受外界侵害。抗性的决定因素包括染色体的四元结构和由蛋白质层组成的细胞外壳（外壳），其组装仍然知之甚少。在这里，通过冷冻聚焦离子束微加工生成的薄片的原位冷冻电子断层扫描为枯草芽孢杆菌孢子囊的超微结构组织提供了深入的了解。重构的断层扫描图像显示，在早期孢子形成过程中，前孢子中的染色体采用具有 5.5nm 厚纤维的环形结构。在同一阶段，前孢子表面的外壳蛋白形成具有不同电子密度、尺寸和组织的无定形或结构化层的堆叠。通过使用冷冻电子断层扫描和树脂切片的透射电子显微镜对突变株进行分析，我们区分了具有不同分子特性的七个新生外壳区域，并提出了外壳形态发生蛋白贡献的模型。
