Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, Netherlands.
Department of Fundamental Microbiology (DMF), Faculty of Biology and Medicine (FBM), University of Lausanne (UNIL), Lausanne, Switzerland.
Nat Commun. 2024 Mar 28;15(1):2737. doi: 10.1038/s41467-024-47094-x.
Bacterial chromosomes are folded into tightly regulated three-dimensional structures to ensure proper transcription, replication, and segregation of the genetic information. Direct visualization of chromosomal shape within bacterial cells is hampered by cell-wall confinement and the optical diffraction limit. Here, we combine cell-shape manipulation strategies, high-resolution fluorescence microscopy techniques, and genetic engineering to visualize the shape of unconfined bacterial chromosome in real-time in live Bacillus subtilis cells that are expanded in volume. We show that the chromosomes predominantly exhibit crescent shapes with a non-uniform DNA density that is increased near the origin of replication (oriC). Additionally, we localized ParB and BsSMC proteins - the key drivers of chromosomal organization - along the contour of the crescent chromosome, showing the highest density near oriC. Opening of the BsSMC ring complex disrupted the crescent chromosome shape and instead yielded a torus shape. These findings help to understand the threedimensional organization of the chromosome and the main protein complexes that underlie its structure.
细菌染色体折叠成紧密调节的三维结构，以确保遗传信息的正确转录、复制和分离。由于细胞壁的限制和光学衍射极限，直接在细菌细胞内观察染色体形状受到阻碍。在这里，我们结合细胞形状操作策略、高分辨率荧光显微镜技术和遗传工程，实时可视化体积扩大的活枯草芽孢杆菌细胞中未受限制的细菌染色体的形状。我们表明，染色体主要呈现出新月形，DNA 密度不均匀，在复制起点（oriC）附近增加。此外，我们沿着新月形染色体的轮廓定位了 ParB 和 BsSMC 蛋白——染色体组织的关键驱动因素，在 oriC 附近显示出最高的密度。BsSMC 环复合物的打开破坏了新月形染色体的形状，而是产生了环形。这些发现有助于理解染色体的三维组织以及构成其结构的主要蛋白质复合物。
