Biology subjects

Laloux, G.

Publications and source records attributed to Laloux, G..

9 recordsLinked to original sources

bioRxiv2026

A polarity-controlled Tad nanomachine enables prey invasion in a bacterial predator

Type IV pili are dynamic surface appendages assembled by envelope-spanning nanomachines that mediate diverse bacterial interactions, yet how these systems are adapted to predatory lifestyles remains poorly understood. Here we investigate the tight adherence (Tad) machinery of the obligate predator Bdellovibrio bacteriovorus. Using inducible CRISPR interference combined with live-cell and microfluidics imaging, we show that the Tad system is essential for prolonged prey attachment and subsequent prey remodeling and invasion. The machinery assembles specifically at the invasive cell pole before prey encounter and is temporally coordinated with the predatory cell cycle. We further demonstrate that polar localization of the Tad machinery depends on the polarity hub RomR. In addition, the atypical TadZA fusion ATPase interacts with RomR, identifying a potential molecular link between polarity control and Tad assembly. Together, our findings reveal how spatiotemporal control of a conserved filament system supports bacterial predation.

microbiology↗

bioRxiv2025

Dynamics and interplay of gene expression and chromosome organization across a predatory lifecycle

The obligate predatory bacterium Bdellovibrio bacteriovorus alternates between a motile attack phase and a growth phase inside another bacterium, during which it undergoes multiple rounds of DNA replication followed by non-binary division and progeny release. How its chromosome is dynamically reorganized across these contrasting states remains unclear. Here, we used synchronized predatory infections combined with time-resolved RNA-seq, Hi-C, ChIP-seq, and quantitative microscopy to map transcriptional activity and chromosome architecture across seven key stages of the predatory lifecycle. We uncover a dramatic shift in nucleoid organization - from an ultra-compact, transcriptionally restricted state in attack-phase cells to a progressively decompacted, ori-centered conformation during intracellular replication. Notably, distinct transcriptional and chromosome folding states not only mark the canonical attack and growth phases, but also critical transitions such as prey invasion, replication onset, and predator division. Temporal gene expression profiles reflect the coordinated regulation of core cellular functions across the predatory cycle. Furthermore, spatial localization of RNA polymerase, ribosomes, DNA-binding proteins, and freely diffusing proteins highlight the tight, cell cycle-dependent coupling between nucleoid compaction, chromosome accessibility, and transcriptional activity. Altogether, our findings reveal the intricate dynamics and coordination of genome folding and gene expression in a complex bacterial cell cycle driven by prey-predator interactions.

microbiology↗

bioRxiv2023

Distinct dynamics and proximity networks of hub proteins at the prey-invading cell pole in a predatory bacterium

In bacteria, cell poles function as subcellular compartments where proteins localize during specific lifecycle stages, orchestrated by polar "hub" proteins. Whereas most described bacteria inherit an "old" pole from the mother cell and a "new" pole from cell division, polarizing cells at birth, non-binary division poses challenges for establishing cell polarity, particularly for daughter cells inheriting only new poles. We investigated polarity dynamics in the obligate predatory bacterium Bdellovibrio bacteriovorus, proliferating through filamentous growth followed by non-binary division within prey bacteria. Monitoring the subcellular localization of two proteins known as polar hubs in other species, RomR and DivIVA, revealed RomR as an early polarity marker in B. bacteriovorus. RomR already marks the future anterior poles of the progeny during the predators growth phase, in a define time window closely following the onset of divisome assembly and the end of chromosome segregation. In contrast to RomRs stable unipolar localization in the progeny, DivIVA exhibits a dynamic pole-to-pole localization. This behaviour changes shortly before division of the elongated predator cell, where DivIVA accumulates at all septa and both poles. In vivo protein interaction networks for DivIVA and RomR, mapped through endogenous miniTurbo-based proximity labeling, further underscore their distinct roles in cell polarization and the importance of the anterior "invasive" cell pole in prey-predator interactions. Our work emphasizes the strict spatiotemporal coordination of cellular processes underlying B. bacteriovorus proliferation, offering insights into the subcellular organization of bacteria with filamentous growth and non-binary division.

microbiology↗

bioRxiv2023

Lifecycle of a predatory bacterium vampirizing its prey through the cell envelope and S-layer

Predatory bacteria feed upon and kill other bacteria in various natural environments. Obligate epibiotic predators like Bdellovibrio exovorus consume their prey whilst remaining attached to the outside of the prey. How these predators achieve epibiotic feeding through the prey cell envelope has not been explored previously. Whereas the S-layer is the only proposed defensive structure against predatory bacteria, it remains unclear how this thin outer layer of the envelope might prevent epibiotic attacks. Similarly, the lifecycle of B. exovorus during the predator-prey interaction is poorly understood, with current models suggesting a binary division. Here we imaged the entire predatory lifecycle of B. exovorus and the fate of its Caulobacter crescentus prey by time-lapse microscopy and cryo-electron microscopy to monitor predator attack, growth and division and assess the impact of the S-layer on epibiotic predation. Our data reveal that B. exovorus uses non-binary division in a novel proliferation pattern that mainly generates three progenies. Moreover, we found that B. exovorus predates regardless of the presence of an S-layer, calling for revisiting its protective role against predators. Finally, our results indicate that epibiotic predation relies on the establishment of a secured junction between the prey and predator outer membranes, which must be resolved unilaterally to maintain cellular integrity of the predator departing from the prey surface.

microbiology↗

bioRxiv2023

Cell cycle-dependent organization of a bacterial centromere through multi-layered regulation of the ParABS system

The accurate distribution of genetic material is crucial for all organisms. In most bacteria, chromosome segregation is achieved by the ParABS system, in which the ParB-bound centromere parS is actively partitioned by ParA. While this system is highly conserved, its adaptation in organisms with unique lifestyles and its regulation between developmental stages remain unexplored. Bdellovibrio bacteriovorus is a predatory bacterium proliferating through polyploid replication and non-binary division inside other bacteria. Our study reveals the subcellular dynamics and multi-layered regulation of the ParABS system, coupled to the cell cycle of B. bacteriovorus. We found that ParA:ParB ratios fluctuate between predation stages, their balance being critical for cell cycle progression. Moreover, the parS chromosomal context in non-replicative cells, combined with ParB depletion at cell division, critically contribute to the unique cell cycle-dependent organization of the centromere in this bacterium, highlighting new levels of complexity in chromosome segregation and cell cycle control. Author summaryThe precise distribution of genetic material to the progeny is essential for all living organisms, and the ParABS system is critical for this process in bacteria. Our study provides novel insights into the regulation of this system in a predatory bacterium that exhibits a non-canonical cell cycle, in which the chromosome is copied and segregated multiple times during growth inside a prey bacterium. Our work reveals the subcellular dynamics and multi-level regulation of the ParABS system in this bacterium, which results in the unique cell-cycle dependent assembly of the segregation complex at the chromosomal centromere. Our findings provide a deeper understanding of the adaptation of the ParABS system across bacterial species and developmental stages.

microbiology↗

bioRxiv2023

Rewiring capsule production by CRISPRi-based genetic oscillators demonstrates a functional role of phenotypic variation in pneumococcal-host interactions

Phenotypic variation is the phenomenon in which clonal cells display different traits even under identical environmental conditions. This plasticity is thought to be important for processes including bacterial virulence1-8, but direct evidence for its relevance is often lacking. For instance, variation in capsule production in the human pathogen Streptococcus pneumoniae has been linked to different clinical outcomes9-14, but the exact relationship between variation and pathogenesis is not well understood due to complex natural regulation15-20. In this study, we used synthetic oscillatory gene regulatory networks (GRNs) based on CRISPR interference together with live cell microscopy and cell tracking within microfluidics devices to mimic and test the biological function of bacterial phenotypic variation. We provide a universally applicable approach for engineering intricate GRNs using only two components: dCas9 and extended sgRNAs (ext-sgRNAs). Our findings demonstrate that variation in capsule production is beneficial for pneumococcal fitness in traits associated with pathogenesis providing conclusive evidence for this longstanding question.

microbiology↗

bioRxiv2023

Apparent simplicity and emergent robustness in bacterial cell cycle control

To examine how bacteria achieve robust cell proliferation across diverse conditions, we developed a method that quantifies 77 cell morphological, cell cycle and growth phenotypes of a fluorescently-labeled Escherichia coli strain and >800 gene deletion derivatives under multiple nutrient conditions. This approach revealed extensive phenotypic plasticity and deviating mutant phenotypes were often found to be nutrient-dependent. From this broad phenotypic landscape emerged simple and robust unifying rules (laws) that connect DNA replication initiation, nucleoid segregation, FtsZ-ring formation, and cell constriction to specific aspects of cell size (volume, length, or added length). Furthermore, completion of cell division followed the initiation of cell constriction after a constant time delay across strains and nutrient conditions, identifying cell constriction as a key control point for cell size determination. Our work provides a systems-level understanding of the design principles by which E. coli integrates cell cycle processes and growth rate with cell size to achieve its robust proliferative capability.

systems biology↗

bioRxiv2022

Modulation of prey size reveals adaptability and robustness in the cell cycle of an intracellular predator

Despite the remarkable diversity of bacterial lifestyles, the sophisticated regulatory networks underlying bacterial replication have only been investigated in a limited number of model species so far. In bacteria that do not rely on canonical binary division for proliferation, the coordination of major cellular processes is still mysterious. Moreover, bacterial growth and division remain largely unexplored within spatially confined niches where nutrients are limited. This includes the lifecycle of the model endobiotic predatory bacterium Bdellovibrio bacteriovorus, which grows by filamentation within its host or prey cells and produces a variable number of daughter cells. Here, we examined how the size of the micro-compartment in which predators replicate (i.e., the prey bacterium) impacts their cell cycle progression at the single-cell level. Using Escherichia coli with genetically encoded size differences, we show that the duration of the predator cell cycle scales with prey size. As a result, the size of the prey determines the number of predator offspring, through a relationship that is maintained across prey species. Strikingly, the nutritional quality of the prey cell determined the specific growth rate of predators regardless of prey size, reminiscent of the effect of medium composition on the growth of other bacteria. Tuning the predatory cell cycle by modulating prey dimensions also allowed us to reveal invariable temporal connections between key cellular processes. Altogether, our data uncover adaptability and robustness shaping the enclosed replication of B. bacteriovorus. Consequently, predators optimally exploit the finite prey resources and space while ensuring a strict cell cycle progression. This study opens the way to explore diverse cell cycle control strategies by extending their characterization to intracellular lifestyles, beyond canonical models and growth conditions.

microbiology↗

bioRxiv2020

Chromosome dynamics and spatial organization during the non-binary cell cycle of a predatory bacterium

In bacteria, the dynamics of chromosome replication and segregation are tightly coordinated with cell cycle progression, and largely rely on specific spatiotemporal arrangement of the chromosome. Whereas these key processes are mostly investigated in species that divide by binary fission, they remain mysterious in bacteria producing larger number of descendants. Here, we establish the predatory bacterium Bdellovibrio bacteriovorus as a model to investigate the non-binary processing of a circular chromosome. Our data reveal its extreme compaction in a dense polarized nucleoid. We also show that a first binary-like cycle of replication and asymmetric segregation is followed by multiple asynchronous rounds of replication and progressive ParABS-dependent partitioning, uncoupled from cell division. Surprisingly, ParB localization at the centromere is cell-cycle regulated. Altogether, our findings support a model of complex chromosome choreography, leading to the generation of variable numbers of offspring, highlighting the adaptation of conserved mechanisms to achieve non-binary reproduction in bacteria.

microbiology↗