DivIVA Controls Progeny Morphology and Diverse ParA Proteins Regulate Cell Division or Gliding Motility in Bdellovibrio bacteriovorus

Role of Orphan ParA Proteins in Replication and Cell Division in Rhodococcus erythropolis PR4

Bacteria have a very well-regulated mechanism for chromosome segregation and cell division. This process requires a large number of complex proteins to participate and mediate their functionality. Among these complex proteins, ParA and ParB play a vital role for the faithful segregation of chromosome. In Rhodococcus erythropolis PR4, besides the essential parAB operon, there are three orphan copies of parA genes. Here, we report that the orphan ParA2 and ParA3 have distinct roles in the cell cycle. The disruption of the orphan parA2 or parA3 gene resulted in elongated cells. Multiple septal rings and mislocalised septa were observed in ΔparA3 and ΔparA2 mutants, respectively. The subcellular localization of ParA2 revealed a distinct ring- and ribbon-like structure. On the other hand, orphan ParA3 was localized slightly away from the poles. The orphan ParA proteins were found to interact with ParB, the strongest interaction was observed with ParA2. Further, asynchronous replication initiation was observed in ΔparA3 mutants suggesting its role in replication. This is the first report demonstrating the distinct roles of orphan parA genes from Rhodococcus.

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, generating cell asymmetry 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 predator's growth phase, during a precise period closely following the onset of divisome assembly and the end of chromosome segregation. In contrast to RomR's stable unipolar localization in the progeny, DivIVA exhibits a dynamic pole-to-pole localization. This behavior changes shortly before the 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 reinforce the importance of the anterior "invasive" cell pole in prey-predator interactions. Our work also emphasizes the precise spatiotemporal order of cellular processes underlying B. bacteriovorus proliferation, offering insights into the subcellular organization of bacteria with filamentous growth and non-binary division.IMPORTANCEIn bacteria, cell poles are crucial areas where "hub" proteins orchestrate lifecycle events through interactions with multiple partners at specific times. While most bacteria exhibit one "old" and one "new" pole, inherited from the previous division event, setting polar identity poses challenges in bacteria with non-binary division. This study explores polar proteins in the predatory bacterium Bdellovibrio bacteriovorus, which undergoes filamentous growth followed by non-binary division inside another bacterium. Our research reveals distinct localization dynamics of the polar proteins RomR and DivIVA, highlighting RomR as an early "hub" marking polar identity in the filamentous mother cell. Using miniTurbo-based proximity labeling, we uncovered their unique protein networks. Overall, our work provides new insights into the cell polarity in non-binary dividing bacteria.

The effect of Bdellovibrio bacteriovorus containing dressing on superficial incisional surgical site infections experimentally induced by Klebsiella pneumoniae in mice

Bdellovibrio bacteriovorus is a bacterial agent that stands out for its ability to act as a predator against gram-negative bacteria and has found application against antibiotic-resistant pathogens. The aim of this study is to determine the efficacy of Bdellovibrio bacteriovorus against antibiotic-resistant pathogens, particularly those causing infections in surgical incision sites. A total of 6 experimental groups were created in mice, and surgical area infections were initiated with Klebsiella pneumoniae in incision sites. The effects of antibiotics and Bdellovibrio bacteriovorus alone or in combination were compared to the control group. In the Bdellovibrio bacteriovorus treatment group, edema and redness were observed in all mice at 24th hours, in 20% of mice at 48th hours, and in none at the 72 nd h. A significant difference was observed in the Bdellovibrio bacteriovorus treatment groups in reducing Klebsiella pneumoniae burden in the incision area compared to antibiotics alone or Bdellovibrio bacteriovorus + antibiotics, (p < 0.001). Likewise, cytokine level determinations indicated that B. bacteriovorus applications generated a therapeutic response without inducing an inflammatory response.

Chromosome structure and DNA replication dynamics during the life cycle of the predatory bacterium Bdellovibrio bacteriovorus

Bdellovibrio bacteriovorus, an obligate predatory Gram-negative bacterium that proliferates inside and kills other Gram-negative bacteria, was discovered more than 60 years ago. However, we have only recently begun to understand the detailed cell biology of this proficient bacterial killer. Bdellovibrio bacteriovorus exhibits a peculiar life cycle and bimodal proliferation, and thus represents an attractive model for studying novel aspects of bacterial cell biology. The life cycle of B. bacteriovorus consists of two phases: a free-living nonreplicative attack phase and an intracellular reproductive phase. During the reproductive phase, B. bacteriovorus grows as an elongated cell and undergoes binary or nonbinary fission, depending on the prey size. In this review, we discuss: (1) how the chromosome structure of B. bacteriovorus is remodeled during its life cycle; (2) how its chromosome replication dynamics depends on the proliferation mode; (3) how the initiation of chromosome replication is controlled during the life cycle, and (4) how chromosome replication is spatiotemporally coordinated with the proliferation program.

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 parS sequence 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 largely 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.

Advances in cellular and molecular predatory biology of Bdellovibrio bacteriovorus six decades after discovery

Since its discovery six decades ago, the predatory bacterium Bdellovibrio bacteriovorus has sparked recent interest as a potential remedy to the antibiotic resistance crisis. Here we give a comprehensive historical overview from discovery to progressive developments in microscopy and molecular mechanisms. Research on B. bacteriovorus has moved from curiosity to a new model organism, revealing over time more details on its physiology and fascinating predatory life cycle with the help of a variety of methods. Based on recent findings in cryo-electron tomography, we recapitulate on the intricate molecular details known in the predatory life cycle including how this predator searches for its prey bacterium, to how it attaches, grows, and divides all from within the prey cell. Finally, the newly developed B. bacteriovorus progeny leave the prey cell remnants in the exit phase. While we end with some unanswered questions remaining in the field, new imaging technologies and quantitative, systematic advances will likely help to unravel them in the next decades.

Binary or Nonbinary Fission? Reproductive Mode of a Predatory Bacterium Depends on Prey Size

Most bacteria, including model organisms such as Escherichia coli, Bacillus subtilis, and Caulobacter crescentus, reproduce by binary fission. However, some bacteria belonging to various lineages, including antibiotic-producing Streptomyces and predatory Bdellovibrio, proliferate by nonbinary fission, wherein three or more chromosome copies are synthesized and the resulting multinucleoid filamentous cell subdivides into progeny cells. Here, we demonstrate for the first time that the predatory bacterium Bdellovibrio bacteriovorus reproduces through both binary and nonbinary fission inside different prey bacteria. Switching between the two modes correlates with the prey size. In relatively small prey cells, B. bacteriovorus undergoes binary fission; the FtsZ ring assembles in the midcell, and the mother cell splits into two daughter cells. In larger prey cells, B. bacteriovorus switches to nonbinary fission and creates multiple asynchronously assembled FtsZ rings to produce three or more daughter cells. Completion of bacterial cell cycle critically depends on precise spatiotemporal coordination of chromosome replication with other cell cycle events, including cell division. We show that B. bacteriovorus always initiates chromosome replication at the invasive pole of the cell, but the spatiotemporal choreography of subsequent steps depends on the fission mode and/or the number of progeny cells. In nonbinary dividing filaments producing five or more progeny cells, the last round(s) of replication may also be initiated at the noninvasive pole. Altogether, we find that B. bacteriovorus reproduces through bimodal fission and that extracellular factors, such as the prey size, can shape replication choreography, providing new insights about bacterial life cycles. IMPORTANCE Most eukaryotic and bacterial cells divide by binary fission, where one mother cell produces two progeny cells, or, rarely, by nonbinary fission. All bacteria studied to date use only one of these two reproduction modes. We demonstrate for the first time that a predatory bacterium, Bdellovibrio bacteriovorus, exhibits bimodal fission and the mode of division depends on the size of the prey bacterium inside which B. bacteriovorus grows. This work provides key insights into the mode and dynamics of B. bacteriovorus proliferation in different pathogens that pose a major threat to human health due to their emerging antibiotic resistance (Proteus mirabilis, Salmonella enterica, and Shigella flexneri). The use of predatory bacteria such as B. bacteriovorus is currently regarded as a promising strategy to kill antibiotic-resistant pathogens. We find that B. bacteriovorus employs different chromosome replication choreographies and division modes when preying on those pathogens. Our findings may facilitate the design of efficient pathogen elimination strategies.

An optimized workflow to measure bacterial predation in microplates

The predatory bacterium Bdellovibrio bacteriovorus invades and proliferates inside other bacteria by non-binary division. Here we describe a fluorescence-based technique for the immediate evaluation of predator density independently of plaque formation, an optimized setup to monitor predation in microplates, and the CuRveR package to quantify both prey killing and predator proliferation dynamics. This protocol allows to assess the impact of mutations or chemicals on predation. CuRveR also constitutes a user-friendly tool to analyze growth or decay data unrelated to predation.

For complete details on the use and execution of this profile, please refer to Kaljević et al., 2021.

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A protocol for routine culturing of Bdellovibrio bacteriovorus predatory bacteria

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A quick fluorescence-based technique to obtain predator cells numbers

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An automated assay of prey killing and predator proliferation in microplates

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The CuRveR package to extract prey decay and predator growth parameters

Bdellovibrio and like organisms: current understanding and knowledge gaps of the smallest cellular hunters of the microbial world

Almost sixty years ago, Bdellovibrio and like organisms (BALOs) were discovered as the first obligate bacterial predators of other bacteria known to science. Since then, they were shown to be diverse and ubiquitous in the environment, and to bear astonishing ecological, physiological, and metabolic capabilities. The last decade has seen important strides made in understanding the mechanistic basis of their life cycle, the dynamics of their interactions with prey, along with significant developments towards their use in medicine, agriculture, and industry. This review details these achievements, identify current understanding and knowledge gaps to encourage and guide future BALO research.

Chromosome choreography 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. We found that its single chromosome is highly compacted in a polarized nucleoid that excludes freely diffusing proteins during the non-proliferative stage of the cell cycle. A binary-like cycle of DNA replication and asymmetric segregation is followed by multiple asynchronous rounds of replication and progressive ParABS-dependent partitioning, uncoupled from cell division. Finally, we provide the first evidence for an on-off behavior of the ParB protein, which localizes at the centromere in a cell-cycle-regulated manner. Altogether, our findings support a model of complex chromosome choreography leading to the generation of variable, odd, or even numbers of offspring and highlight the adaptation of conserved mechanisms to achieve non-binary reproduction.

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The Bdellovibrio chromosome is polarized, with ori located near the invasive pole

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The highly compacted nucleoid excludes cytosolic proteins in non-replicative cells

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Replication and segregation of chromosomes are uncoupled from cell division

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The centromeric protein ParB localizes at parS in a cell-cycle-dependent manner

Predatory bacteria as living antibiotics - where are we now?

Antimicrobial resistance (AMR) is a global health and economic crisis. With too few antibiotics in development to meet current and anticipated needs, there is a critical need for new therapies to treat Gram-negative infections. One potential approach is the use of living predatory bacteria, such as Bdellovibrio bacteriovorus (small Gram-negative bacteria that naturally invade and kill Gram-negative pathogens of humans, animals and plants). Moving toward the use of Bdellovibrio as a 'living antibiotic' demands the investigation and characterization of these bacterial predators in biologically relevant systems. We review the fundamental science supporting the feasibility of predatory bacteria as alternatives to antibiotics.

The unusual cell wall of the Lyme disease spirochaete Borrelia burgdorferi is shaped by a tick sugar

Peptidoglycan-a mesh sac of glycans that are linked by peptides-is the main component of bacterial cell walls. Peptidoglycan provides structural strength, protects cells from osmotic pressure and contributes to shape. All bacterial glycans are repeating disaccharides of N-acetylglucosamine (GlcNAc) β-(1-4)-linked to N-acetylmuramic acid (MurNAc). Borrelia burgdorferi, the tick-borne Lyme disease pathogen, produces glycan chains in which MurNAc is occasionally replaced with an unknown sugar. Nuclear magnetic resonance, liquid chromatography-mass spectroscopy and genetic analyses show that B. burgdorferi produces glycans that contain GlcNAc-GlcNAc. This unusual disaccharide is chitobiose, a component of its chitinous tick vector. Mutant bacteria that are auxotrophic for chitobiose have altered morphology, reduced motility and cell envelope defects that probably result from producing peptidoglycan that is stiffer than that in wild-type bacteria. We propose that the peptidoglycan of B. burgdorferi probably evolved by adaptation to obligate parasitization of a tick vector, resulting in a biophysical cell-wall alteration to withstand the atypical torque associated with twisting motility.