Direct observation of a crescent-shape chromosome in expanded Bacillus subtilis cells

• Published in: Nature communications Vol. 15; no. 1; p. 2737
• Main Authors: Tišma, Miloš, Bock, Florian Patrick, Kerssemakers, Jacob, Antar, Hammam, Japaridze, Aleksandre, Gruber, Stephan, Dekker, Cees
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 28-03-2024; Nature Publishing Group; Nature Portfolio
• Subjects: 14/63; 631/326/41; 631/57; Bacillus subtilis; Bacillus subtilis - genetics; Bacillus subtilis - metabolism; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Cell size; Chromosome Segregation - genetics; Chromosomes; Chromosomes, Bacterial - genetics; Chromosomes, Bacterial - metabolism; Confinement; Density; DNA Replication - genetics; DNA, Bacterial - metabolism; Fluorescence microscopy; Genetic engineering; Humanities and Social Sciences; multidisciplinary; Origin Recognition Complex - metabolism; Proteins; Replication; Replication Origin; Replication origins; Science; Science (multidisciplinary); Toruses
• ISSN: 2041-1723; 2041-1723
• 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.
The spatial structure of the bacterial chromosome is resolved in the absence of confinement by the cell boundary. Size-expanded cells reveal a crescent-shaped
Bacillus
subtilis
chromosome and the effects of ParB and SMC proteins on chromosome shape.