How do bacteria divide? At first glance, it might seem simple: one cell splits into two. But behind this universal process lies a fascinating diversity of strategies, shaped by evolution, bacterial morphology and environment. Our recent study [1] sheds light on a particularly unusual case—the cell division of Deinococcus radiodurans, a bacterium renowned for surviving extreme doses of radiation.
Unlike most bacteria, D. radiodurans divides using a “sliding doors” mechanism. Instead of the cell wall closing like an iris or a diaphragm from all around the cell periphery, two new cell walls with flat leading edges grow inward from opposite sides of the cell, meeting and fusing at mid-cell. This curious strategy has long puzzled scientists, who wondered how such a complex division process is coordinated and achieved.
To tackle this question, researchers from the I2SR, MICA and PG groups at IBS combined cuttingedge imaging approaches (Figure 1A-B). Live fluorescence microscopy (conventional confocal microscopy and single-molecule localization microscopy) performed on the M4D imaging platform of the IBS/ISBG allowed them to watch dividing cells in real time, while cryo-electron tomography performed at the Umeå Centre for Electron Microscopy in Sweden, on thin, frozen lamellae of the bacteria, revealed various cell division intermediates and the cell wall’s fine architecture at each step of the process. This powerful combination uncovered the complex layered structure of the bacterium’s envelope and showed how the “sliding doors” septa grow, straighten, and fuse (Figure 2).
One striking discovery was the presence of thin membrane protrusions at the tips of the growing septa (Figure 1C). These flexible extensions may help align the two sides before they fuse. Another key player is FtsZ, a highly conserved protein that assembles into filaments at the division site [2]. In this study, FtsZ and its membrane anchor, FtsA, were found to form a double-arched structure at the tip of growing septa bearing a thick, rigid peptidoglycan layer (Figure 1D). These findings suggest that FtsZ plays a role in the rigidification of the septa by regulating the location of the peptidoglycan synthesis machinery with which it interacts.
Beyond revealing the mechanics of cell division, this work raises intriguing questions: why does D. radiodurans use such an unusual and elaborate strategy to divide? Although we do not have the answer to this question, we postulate that its unusual cell envelope composition, its cell morphology (diads and tetrads), and its remarkable resilience to DNA damage may have shaped this distinctive mode of division, potentially offering advantages in
surviving extreme stress.
This work was the result of a true collaborative effort between three IBS teams with complementary expertise who joined forces to unlock mysteries of microbial life. This study is important not only because it reveals how one of the toughest bacteria on Earth orchestrates its division process, but also because it could inspire new strategies to combat microbes and the growing threat of antibiotic resistance.
J. Timmins, I. Gutsche and JP. Kleman (IBS)
[1] Gaifas L, Kleman JP, Lacroix F, Schexnaydre E et al. (2025) PNAS,122, e2425047122.
[2] Barrows JM and Goley ED (2020) Curr Opin Cell Biol., 68, 163-172.
Figure 1: (A) High-resolution PAINT image of Nile Red-stained D. radiodurans membranes. (B) Left: Schematic diagram of a dividing D. radiodurans diad (twocell unit) in the process of becoming a tetrad (four-cell unit). Right: Central slice of a typical cryo-electron tomogram of an actively dividing D. radiodurans diad. The field of view corresponds to the dashed red box presented on the left. The multilayered cell envelope is composed notably of the inner (black line) and outer (red line) membranes and a thick peptidoglycan layer (green line). The light gray density in the center of the cell delimited with a dashed white line corresponds to the nucleoid and the small dark densities distributed throughout the cytoplasm (and excluded from the nucleoid) are ribosomes. (C) Examples of tubular and curved membrane protrusions observed at the tips of growing septa, devoid of peptidoglycan. (D) Left: Top and side views of confocal images of dual-labelled D. radiodurans: Nile Red staining of the cell membrane and green labelling of FtsZ. Middle: Close-up view of a septal tip bearing a doublarched structure composed of FtsZ (blue) and FtsA (purple) filaments oriented perpendicular to the image plane. Right: Model of FtsA/FtsZ arrangement at the tip of growing septa in close proximity to the site of peptidoglycan synthesis.
Figure 2: Schematic model of the ‘sliding doors’ septation process in D. radiodurans.