Uncovering the choreography of the chromosome during the non-binary cell cycle of the predatory bacterium Bdellovibrio bacteriovorus
(2019) BSM — Location: Brussels
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- Abstract
- Bdellovibrio species are predatory d-proteobacteria that invade the periplasm of other Gram-negative bacteria. The prey bacterium forms a structure termed “bdelloplast” whereas the predator grows in its periplasm as a filament before dividing at once into a variable number of monoploid cells by a nonbinary division process. This remarkable lifestyle is at odds with textbook models of binary proliferation and raises a series of intriguing biological questions. Yet, molecular understanding of how this micropredator proliferates inside the envelope of other bacteria is still missing. One of the biggest challenges that cells face is to keep chromosome structured and to ensure proper coordination of its replication and segregation before cell division. In the case of Bdellovibrio, additional complexity arises as the growing predator must copy its single chromosome multiple times before cell division. Most bacteria possess a single circular chromosome where subcellular location of key landmarks, origin of replication (ori) and terminus region (ter), varies among species and is critical for cell cycle progression. However, the spatiotemporal arrangement of the Bdellovibrio chromosome is mainly unknown. Moreover, the mechanism and spatiotemporal coordination of chromosome segregation with DNA replication and cell division, have remained unexplored in Bdellovibrio. Our first goal is to determine how the essential chromosomal regions are positioned throughout the cell cycle of Bdellovibrio. The localization of ori and ter regions is tracked by inserting synthetic sequences with high affinities towards fluorescent proteins which can be observed via microscopy. Our results suggest that the circular chromosome exhibits a specific orientation in the non-proliferating cell that is maintained at least in early stages of predation. Our observations also reveal intriguing dynamics of the level of nucleoid compaction in Bdellovibrio. Furthermore, in order to gain insight into the segregation machinery of Bdellovibrio, we aimed to investigate the homologues of the tripartite segregation system ParABS using subcellular localization in living cells, bacterial genetics and protein-protein interaction assays. Our recent findings shed light on essential and original features of these predatory bacteria supporting the idea that bacterial nucleoids are complex and dynamic entities tightly coupled to cell cycle progression and growth phase.
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Kaljevic, J. (2019). Uncovering the choreography of the chromosome during the non-binary cell cycle of the predatory bacterium Bdellovibrio bacteriovorus. BSM, Brussels. https://hdl.handle.net/2078.5/238289