Prey Cells Research Articles

Grazing Pressure Is Independent of Prey Size in a Generalist Herbivorous Protist: Insights from Experimental Temperature Gradients.

Grazing by herbivorous protists contributes to structuring plankton communities through its effect on the growth, biomass, and competitiveness of prey organisms and also impacts the transfer of primary production towards higher trophic levels. Previous evidence shows that heterotrophic processes (grazing rates, g) are more sensitive to temperature than autotrophic ones (phytoplankton growth rates, μ) and also that small cells tend to be more heavily predated than larger ones; however, it remains unresolved how the interplay between changes in temperature and cell size modulates grazing pressure (i.e., g:μ ratio). We addressed this problem by conducting an experiment with four phytoplankton populations, from pico- to microphytoplankton, over a 12°C gradient and in the presence/absence of a generalist herbivorous protist, Oxyrrhis marina. We found that highest g rates coincided with highest μ rates, which corresponded to intermediate cell sizes. There were no significant differences in either μ or g between the smallest and largest cell sizes considered. The g:μ ratio was largely independent of cell size and C:N ratios, and its thermal dependence was low although species-specific differences were large. We suggest that the similar g:μ found could be the consequence that the energetic demand imposed by rising temperatures would be a more important issue than the mechanical constriction to ingestion derived from prey cell size. Despite the difficulty of quantifying μ and g in natural planktonic communities, we suggest that the g:μ ratio is a key response variable to evaluate thermal sensitivity of food webs because it gives a more integrative view of trophic functioning than both rates separately.

Anaerobic metabolism of Foraminifera thriving below the seafloor

Foraminifera are single-celled eukaryotes (protists) of large ecological importance, as well as environmental and paleoenvironmental indicators and biostratigraphic tools. In addition, they are capable of surviving in anoxic marine environments where they represent a major component of the benthic community. However, the cellular adaptations of Foraminifera to the anoxic environment remain poorly constrained. We sampled an oxic-anoxic transition zone in marine sediments from the Namibian shelf, where the genera Bolivina and Stainforthia dominated the Foraminifera community, and use metatranscriptomics to characterize Foraminifera metabolism across the different geochemical conditions. Relative Foraminifera gene expression in anoxic sediment increased an order of magnitude, which was confirmed in a 10-day incubation experiment where the development of anoxia coincided with a 20–40-fold increase in the relative abundance of Foraminifera protein encoding transcripts, attributed primarily to those involved in protein synthesis, intracellular protein trafficking, and modification of the cytoskeleton. This indicated that many Foraminifera were not only surviving but thriving, under the anoxic conditions. The anaerobic energy metabolism of these active Foraminifera was characterized by fermentation of sugars and amino acids, fumarate reduction, and potentially dissimilatory nitrate reduction. Moreover, the gene expression data indicate that under anoxia Foraminifera use the phosphogen creatine phosphate as an ATP store, allowing reserves of high-energy phosphate pool to be maintained for sudden demands of increased energy during anaerobic metabolism. This was co-expressed alongside genes involved in phagocytosis and clathrin-mediated endocytosis (CME). Foraminifera may use CME to utilize dissolved organic matter as a carbon and energy source, in addition to ingestion of prey cells via phagocytosis. These anaerobic metabolic mechanisms help to explain the ecological success of Foraminifera documented in the fossil record since the Cambrian period more than 500 million years ago.

Live-Cell Imaging of the Life Cycle of Bacterial Predator Bdellovibrio bacteriovorus using Time-Lapse Fluorescence Microscopy.

Bdellovibrio bacteriovorus is a small gram-negative, obligate predatory bacterium that kills other gram-negative bacteria, including harmful pathogens. Therefore, it is considered a living antibiotic. To apply B. bacteriovorus as a living antibiotic, it is first necessary to understand the major stages of its complex life cycle, particularly its proliferation inside prey. So far, it has been challenging to monitor successive stages of the predatory life cycle in real-time. Presented here is a comprehensive protocol for real-time imaging of the complete life cycle of B. bacteriovorus, especially during its growth inside the host. For this purpose, a system consisting of an agarose pad is used in combination with cell-imaging dishes, in which the predatory cells can move freely beneath the agarose pad while immobilized prey cells are able to form bdelloplasts. The application of a strain producing a fluorescently tagged β-subunit of DNA polymerase III further allows chromosome replication to be monitored during the reproduction phase of the B. bacteriovorus life cycle.

Predatory protists.

The vast majority of eukaryotic life is made up of single cells commonly referred to as protists. In this primer, Leander provides an introduction to predatory protists - cells that eat other cells. This lifestyle, in particular the use of phagocytosis, makes endosymbiosis possible and enabled the evolution of complex cells.

Crosstalk between the Type VI Secretion System and the Expression of Class IV Flagellar Genes in the Pseudomonas fluorescens MFE01 Strain.

Type VI secretion systems (T6SSs) are contractile bacterial multiprotein nanomachines that enable the injection of toxic effectors into prey cells. The Pseudomonas fluorescens MFE01 strain has T6SS antibacterial activity and can immobilise competitive bacteria through the T6SS. Hcp1 (hemolysin co-regulated protein 1), a constituent of the T6SS inner tube, is involved in such prey cell inhibition of motility. Paradoxically, disruption of the hcp1 or T6SS contractile tail tssC genes results in the loss of the mucoid and motile phenotypes in MFE01. Here, we focused on the relationship between T6SS and flagella-associated motility. Electron microscopy revealed the absence of flagellar filaments for MFE01Δhcp1 and MFE01ΔtssC mutants. Transcriptomic analysis showed a reduction in the transcription of class IV flagellar genes in these T6SS mutants. However, transcription of fliA, the gene encoding the class IV flagellar sigma factor, was unaffected. Over-expression of fliA restored the motile and mucoid phenotypes in both MFE01Δhcp1+fliA, and MFE01ΔtssC+fliA and a fliA mutant displayed the same phenotypes as MFE01Δhcp1 and MFE01ΔtssC. Moreover, the FliA anti-sigma factor FlgM was not secreted in the T6SS mutants, and flgM over-expression reduced both motility and mucoidy. This study provides arguments to unravel the crosstalk between T6SS and motility.

Persicimonas caeni gen. nov., sp. nov., the Representative of a Novel Wide-Ranging Predatory Taxon in Bradymonadales.

A novel bacterial strain, designated YN101T, was isolated from a marine solar saltern in the coast of Weihai, Shandong Province, China. Strain YN101T was Gram-stain negative, facultatively anaerobic, oxidase and catalase negative bacterium with the ability to prey on other microbes. A cross-streaking culture method was utilized to analyze the predatory activity of strain YN101T. The results showed strain YN101T could prey on various bacteria, either Gram-stain negative or Gram-stain positive. According to the predatory assays, different species in the same genus may behave differently when attacked by strain YN101T. The predatory behavior of strain YN101T to four typical species was analyzed, and furthermore, predation to Algoriphagus marinus am2T were quantitatively studied by fluorogenic quantitative PCR, and the gene copies decreased over two magnitudes. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain YN101T shared the greatest sequence similarity of 93.9% to Bradymonas sediminis FA350T. The complete genome sequence of strain YN101T was 8,047,306 bp in size and the genomic DNA G + C content was 63.8 mol%. The digital DNA-DNA hybridization (dDDH) values and average nucleotide identity (ANI) values between strain YN101T and B. sediminis FA350T were 13.9 and 74.0%. The genetic features showed that the biosynthesis of many important compounds was deficient in genome of strain YN101T, which may lead to its predation. Moreover, its genome encoded many genes affiliated with type IV pili, secretion system, membrane proteins and transduction proteins. Similar with myxobacteria and Bdellovibrio and like organisms (BALOs), these genes should play important roles in motility, adhesion or virulence to attack prey cells during predation. The predominant polar lipid profile of strain YN101T consisted of phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), and one unidentified aminophospholipid (APL). The major cellular fatty acid of strain YN101T was iso-C17:0, and the sole respiratory quinone was MK-7. Based on the chemotaxonomic, physiological and biochemical characteristics, strain YN101T represents a novel species of a novel genus in the family Bradymonadaceae, for which the name Persicimonas caeni gen. nov., sp. nov. is proposed. The type strain is YN101T (=KCTC 72083T = MCCC 1H00374T).

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

The predatory bacterium B. bacteriovorus grows and divides inside the periplasm of Gram-negative bacteria, forming a structure known as a bdelloplast. Cell division of predators inside the dead prey cell is not by binary fission but instead by synchronous division of a single elongated filamentous cell into odd or even numbers of progeny cells. Bdellovibrio replication and cell division processes are dependent on the finite level of nutrients available from inside the prey bacterium. The filamentous growth and division process of the predator maximizes the number of progeny produced by the finite nutrients in a way that binary fission could not. To learn more about such an unusual growth profile, we studied the role of DivIVA in the growing Bdellovibrio cell. This protein is well known for its link to polar cell growth and spore formation in Gram-positive bacteria, but little is known about its function in a predatory growth context. We show that DivIVA is expressed in the growing B. bacteriovorus cell and controls cell morphology during filamentous cell division, but not the number of progeny produced. Bacterial Two Hybrid (BTH) analysis shows DivIVA may interact with proteins that respond to metabolic indicators of amino-acid biosynthesis or changes in redox state. Such changes may be relevant signals to the predator, indicating the consumption of prey nutrients within the sealed bdelloplast environment. ParA, a chromosome segregation protein, also contributes to bacterial septation in many species. The B. bacteriovorus genome contains three ParA homologs; we identify a canonical ParAB pair required for predatory cell division and show a BTH interaction between a gene product encoded from the same operon as DivIVA with the canonical ParA. The remaining ParA proteins are both expressed in Bdellovibrio but are not required for predator cell division. Instead, one of these ParA proteins coordinates gliding motility, changing the frequency at which the cells reverse direction. Our work will prime further studies into how one bacterium can co-ordinate its cell division with the destruction of another bacterium that it dwells within.

From the Inside Out: an Epibiotic Bdellovibrio Predator with an Expanded Genomic Complement

Bdellovibrio and like organisms are abundant environmental parasitoids of prokaryotes that show diverse predation strategies. The vast majority of studied Bdellovibrio bacteria and like organisms deploy intraperiplasmic replication inside the prey cell, while few isolates with smaller genomes consume their prey from the outside in an epibiotic manner. The novel parasitoid "Candidatus Bdellovibrio qaytius" was isolated from a eutrophic freshwater pond in British Columbia, where it was a continual part of the microbial community. "Ca Bdellovibrio qaytius" was found to preferentially prey on the betaproteobacterium Paraburkholderia fungorum without entering the periplasm. Despite its epibiotic replication strategy, "Ca Bdellovibrio" encodes a large genomic complement more similar to that of complex periplasmic predators. Functional genomic annotation further revealed several biosynthesis pathways not previously found in epibiotic predators, indicating that "Ca Bdellovibrio" represents an intermediate phenotype and at the same time narrowing down the genomic complement specific to epibiotic predators. In phylogenetic analysis, "Ca Bdellovibrio qaytius" occupies a widely distributed, but poorly characterized, basal cluster within the genus Bdellovibrio This suggests that epibiotic predation might be a common predation type in nature and that epibiotic predation could be the ancestral predation type in the genus.IMPORTANCE Bdellovibrio and like organisms are bacteria that prey on other bacteria and are widespread in the environment. Most of the known Bdellovibrio species enter the space between the inner and outer prey membrane, where they consume their prey cells. However, one Bdellovibrio species has been described that consumes its prey from the outside. Here, we describe "Ca Bdellovibrio qaytius," a novel member of the genus Bdellovibrio that also remains outside the prey cell throughout its replication cycle. Unexpectedly, the genome of "Ca Bdellovibrio" is much more similar to the genomes of intracellular predators than to the species with a similar life cycle. Since "Ca Bdellovibrio" is also a basal representative of this genus, we hypothesize that extracellular predation could be the ancestral predation strategy.

Non-photochemical quenching, a non-invasive probe for monitoring microalgal grazing: influence of grazing-mediated total ammonia-nitrogen

ABSTRACT Contaminant invasion is one of the risks associated with microalgal cultivation in open raceway ponds, and the presence of zooplankton predators often results in a pond culture crash. For effective pond management, an early grazer-detection tool is needed to implement timely interventions. Microalgae and their predators co-exist in the pelagic food web and microalgal prey species have evolved to detect and mount physiological responses against the predator. However, algal prey-predator interactions in mass cultivation are poorly understood. This study aimed to understand the causal relationship between prey photosynthetic physiology, particularly non-photochemical quenching (NPQ), and predator infestation. We used the high biomass and glycerol-accumulating green algal species Dunaliella tertiolecta and the dinoflagellate Oxyrrhis marina as the prey and predator, respectively. Measurement of photosynthetic parameters suggests that NPQ levels significantly drop in the grazing culture, which may be related to increased total ammonia-nitrogen (TAN) accumulation by prey cells. This study suggests using an integrated approach by using NPQ and TAN measurements for early detection of predator infestation.

Non-photochemical quenching, a non-invasive probe for monitoring microalgal grazing: an early indicator of predation by Oxyrrhis marina and Euplotes sp.

ABSTRACT Microalgae are major primary producers in aquatic environments, and many synthesize an array of industrially important biomolecules such as pigments, lipids and proteins. As a result, there is considerable interest in and effort into growing algae for industrial purposes. An economical method to produce a large amount of biomass is the use of the open-raceway pond cultivation platform. However, the nature of the cultivation and the nutrient-rich profile of such cultures attract contaminants such as zooplankton predators, which can result in a sudden culture crash. For effective pond management, an early indicator of grazer presence is needed to implement timely interventions. Currently available tools are offline, time-consuming and dependent on predator concentration. This study explores grazing-mediated changes in photosynthetic parameters during infestation of Dunaliella tertiolecta cultures by the heterotrophic dinoflagellate Oxyrrhis marina and the ciliate Euplotes sp. A significant reduction in non-photochemical quenching levels 24–48 h prior to the crash was observed in both bulk and single-cell prey samples. An increasing rate of grazer ingestion correlated with decreasing non-photochemical quenching levels as the culture progressed towards the crash. The reductions in the non-photochemical quenching levels were consistent in grazing cultures at different prey cell concentrations. Although the maximum photosynthetic yield remained unaltered, maximum relative electron transport rates were enhanced and the light-harvesting efficiency, alpha, reduced in comparison to controls. We suggest that, along with traditional methods, non-photochemical quenching monitoring could be used as a part of integrative pest management to minimize predator outbreaks.

Dynamics of Solitary Predation by Myxococcus xanthus on Escherichia coli Observed at the Single-Cell Level.

The predatory behavior of Myxococcus xanthus has attracted extensive attention due to its unique social traits and inherent biological activities. In addition to group hunting, individual M. xanthus cells are able to kill and lyse prey cells; however, there is little understanding of the dynamics of solitary predation. In this study, by employing a bacterial tracking technique, we investigated M. xanthus predatory dynamics on Escherichia coli at the single-cell level. The killing and lysis of E. coli by a single M. xanthus cell was monitored in real time by microscopic observation, and the plasmolysis of prey cells was identified at a relatively early stage of solitary predation. After quantitative characterization of their solitary predatory behavior, M. xanthus cells were found to respond more dramatically to direct contact with live E. coli cells than heat-killed or UV-killed cells, showing slower predator motion and faster lysing of prey. Among the three contact-dependent killing modes classified according to the major subareas of M. xanthus cells in contact with prey, leading pole contact was observed most. After killing the prey, approximately 72% of M. xanthus cells were found to leave without thorough degradation of the lysed prey, and this postresidence behavior is described as a lysis-leave pattern, indicating that solitary predation has low efficiency in terms of prey-cell consumption. Our results provide a detailed description of the single-cell level dynamics of M. xanthus solitary predation from both prey and predator perspectives.IMPORTANCE Bacterial predation plays multiple essential roles in bacterial selection and mortality within microbial ecosystems. In addition to its ecological and evolutionary importance, many potential applications of bacterial predation have been proposed. The myxobacterium Myxococcus xanthus is a well-known predatory member of the soil microbial community. Its predation is commonly considered a collective behavior comparable to a wolf pack attack; however, individual M. xanthus cells are also able to competently lead to the lysis of a prey cell. Using a bacterial tracking technique, we are able to observe and analyze solitary predation by M. xanthus on Escherichia coli at the single-cell level and reveal the dynamics of both predator and prey during the process. The present study will not only provide a comprehensive understanding of M. xanthus solitary predation but also help to explain why M. xanthus often displays multicellular characteristic predatory behaviors in nature, while a single cell is capable of predation.

The Predation Strategy of Myxococcus xanthus.

Myxobacteria are ubiquitous in soil environments. They display a complex life cycle: vegetatively growing cells coordinate their motility to form multicellular swarms, which upon starvation aggregate into large fruiting bodies where cells differentiate into spores. In addition to growing as saprophytes, Myxobacteria are predators that actively kill bacteria of other species to consume their biomass. In this review, we summarize research on the predation behavior of the model myxobacterium Myxococcus xanthus, which can access nutrients from a broad spectrum of microorganisms. M. xanthus displays an epibiotic predation strategy, i.e., it induces prey lysis from the outside and feeds on the released biomass. This predatory behavior encompasses various processes: Gliding motility and induced cell reversals allow M. xanthus to encounter prey and to remain within the area to sweep up its biomass, which causes the characteristic “rippling” of preying populations. Antibiotics and secreted bacteriolytic enzymes appear to be important predation factors, which are possibly targeted to prey cells with the aid of outer membrane vesicles. However, certain bacteria protect themselves from M. xanthus predation by forming mechanical barriers, such as biofilms and mucoid colonies, or by secreting antibiotics. Further understanding the molecular mechanisms that mediate myxobacterial predation will offer fascinating insight into the reciprocal relationships of bacteria in complex communities, and might spur application-oriented research on the development of novel antibacterial strategies.

Phagocytosis-like cell engulfment by a planctomycete bacterium

Phagocytosis is a key eukaryotic feature, conserved from unicellular protists to animals, that enabled eukaryotes to feed on other organisms. It could also be a driving force behind endosymbiosis, a process by which α-proteobacteria and cyanobacteria evolved into mitochondria and plastids, respectively. Here we describe a planctomycete bacterium, ‘Candidatus Uab amorphum’, which is able to engulf other bacteria and small eukaryotic cells through a phagocytosis-like mechanism. Observations via light and electron microscopy suggest that this bacterium digests prey cells in specific compartments. With the possible exception of a gene encoding an actin-like protein, analysis of the ‘Ca. Uab amorphum’ genomic sequence does not reveal any genes homologous to eukaryotic phagocytosis genes, suggesting that cell engulfment in this microorganism is probably not homologous to eukaryotic phagocytosis. The discovery of this “phagotrophic” bacterium expands our understanding of the cellular complexity of prokaryotes, and may be relevant to the origin of eukaryotic cells.

DNA Uptake upon T6SS-Dependent Prey Cell Lysis Induces SOS Response and Reduces Fitness of Acinetobacter baylyi

Certain Gram-negative bacteria use the type VI secretion system (T6SS) to kill and lyse competing bacteria. Here, we show that the T6SS-dependent lysis of prey cells by the naturally competent Acinetobacter baylyi results in the extensive filamentation of a subpopulation of A.baylyi cells. Filamentation is dependent on the release of DNA from the prey and its uptake by the competence system. The analysis of A.baylyi transcriptome and the response of transcriptional reporters suggest that the uptake of DNA results in the upregulation of the SOS response, which often leads to cell-division arrest. Long-term competition between competent and non-competent strains shows that the strain lacking the DNA uptake machinery outcompetes the parental strain only in the presence of the T6SS-dependent lysis of prey cells. Our data suggest that the cost of the induced SOS response may drive the selection of tight regulation or the loss of DNA uptake in bacteria capable of lysing their competitors.

Bacillus licheniformis escapes from Myxococcus xanthus predation by deactivating myxovirescin A through enzymatic glucosylation.

Myxococcus xanthus kills susceptible bacteria using myxovirescin A (TA) during predation. However, whether prey cells in nature can escape M. xanthus by developing resistance to TA is unknown. We observed that many field-isolated Bacillus licheniformis strains could survive encounters with M. xanthus, which was correlated to their TA resistance. A TA glycoside was identified in the broth of predation-resistant B. licheniformis J32 co-cultured with M. xanthus, and a glycosyltransferase gene (yjiC) was up-regulated in J32 after the addition of TA. Hetero-expressed YjiC-modified TA to a TA glucoside (TA-Gluc) by conjugating a glucose moiety to the C-21 hydroxyl group, and the resulting compound was identical to the TA glycoside present in the co-culture broth. TA-Gluc exhibited diminished bactericidal activity due to its weaker binding with LspA, as suggested by in silico docking data. Heterologous expression of the yjiC gene conferred both TA and M. xanthus-predation resistance to the host Escherichia coli cells. Furthermore, under predatory pressure, B. licheniformis Y071 rapidly developed predation resistance by acquiring TA resistance through the overexpression of yjiC and lspA genes. These results suggest that M. xanthus predation resistance in B. licheniformis is due to the TA deactivation by glucosylation, which is induced in a predator-mediated manner.

Assessment of predatory bacteria and prey interactions using culture-based methods and EMA-qPCR

Traditional culture-based enumeration methods were compared with the ethidium monoazide quantitative polymerase chain reaction (EMA-qPCR) technique to assess Bdellovibrio-and-like-organisms (BALOs) predator-prey interactions. Gram-negative [Pseudomonas spp. and Klebsiella pneumoniae (K. pneumoniae)] and Gram-positive [Staphylococcus aureus (S. aureus) and Enterococcus faecium (E. faecium)] organisms were employed as prey cells, while a Bdellovibrio bacteriovorus strain (PF13) was used as the predator. The co-culture experiments were also compared in diluted nutrient broth (DNB) and HEPES buffer. In both media, K. pneumoniae (maximum log reduction of 5.13) and Pseudomonas fluorescens (P. fluorescens) (maximum log reduction of 4.21) were sensitive to predation by B. bacteriovorus PF13 as their cell counts and gene copies were reduced during all the co-culture experiments, while the concentration of B. bacteriovorus PF13 increased. The concentration of B. bacteriovorus PF13 also increased in the presence of S. aureus (HEPES buffer) and E. faecium (DNB), indicating that the predator interacted with these Gram-positive prey in order to survive. Moreover, as no predator plaques were produced in the co-culture experiments with P. aeruginosa (DNB and HEPES buffer), S. aureus (DNB and HEPES buffer) and E. faecium (HEPES buffer), EMA-qPCR proved to be beneficial in monitoring the concentration of B. bacteriovorus. In conclusion, the cell counts and/or EMA-qPCR analysis for the HEPES buffer and DNB assays were successfully employed to monitor the predation of P. fluorescens and K. pneumoniae by B. bacteriovorus, while E. faecium was sensitive to predation in DNB and S. aureus was sensitive to predation in HEPES buffer.

De novo transcriptome of the newly described phototrophic dinoflagellate Yihiella yeosuensis: comparison between vegetative cells and cysts

Dinoflagellates are often responsible for red tides or harmful algal blooms. Many dinoflagellates move quickly to capture prey cells, escape from predation, and conduct diurnal vertical migrations, but they form cysts (non-motile stage) when growth conditions are not favorable. To investigate differences in gene expression between vegetative cells and cysts of dinoflagellates, transcriptomes of the newly described dinoflagellate Yihiella yeosuensis, one of the fastest dinoflagellates, at the cysts and vegetative cells were de novo assembled. The gene expression profiles of Y. yeosuensis showed 5479 up-regulated and 4790 down-regulated significantly differentially expressed genes, when cells changed from the vegetative cells to cysts. In particular, ‘polyketide synthase’ and ‘cell-wall biogenesis’ genes, related to anti-predation, were highly up-regulated, whereas flagellum-related genes, related to motility, were generally down-regulated. Among the flagellum-related genes of Y. yeosuensis, the ‘central pair’ and ‘radial spoke’ genes, related to direct flagellar movement, were most down-regulated genes. When approximately a hundred flagellum-related genes of motile and non-motile microalgae and plants were analyzed, the number of the genes increased with increasing motility, and furthermore, there was a considerable difference in the presence of the ‘central pair’ and ‘radial spoke’ genes among the motile microalgae. Therefore, high down-regulation of the ‘central pair’ and ‘radial spoke’ genes when Y. yeosuensis cells change from the motile to non-motile stage is possibly related to the presence of these genes in microalgae and plants in their evolution. Conclusively, when Y. yeosuensis form cysts, motility might trade off with anti-predation.

Dynamics of Chromosome Replication and Its Relationship to Predatory Attack Lifestyles in Bdellovibrio bacteriovorus.

Bdellovibrio bacteriovorus is a small Gram-negative, obligate predatory bacterium that is largely found in wet, aerobic environments (e.g., soil). This bacterium attacks and invades other Gram-negative bacteria, including animal and plant pathogens. The intriguing life cycle of B. bacteriovorus consists of two phases: a free-living nonreplicative attack phase, in which the predatory bacterium searches for its prey, and a reproductive phase, in which B. bacteriovorus degrades a host's macromolecules and reuses them for its own growth and chromosome replication. Although the cell biology of this predatory bacterium has gained considerable interest in recent years, we know almost nothing about the dynamics of its chromosome replication. Here, we performed a real-time investigation into the subcellular localization of the replisome(s) in single cells of B. bacteriovorus Our results show that in B. bacteriovorus, chromosome replication takes place only during the reproductive phase and exhibits a novel spatiotemporal arrangement of replisomes. The replication process starts at the invasive pole of the predatory bacterium inside the prey cell and proceeds until several copies of the chromosome have been completely synthesized. Chromosome replication is not coincident with the predator cell division, and it terminates shortly before synchronous predator filament septation occurs. In addition, we demonstrate that if this B. bacteriovorus life cycle fails in some cells of Escherichia coli, they can instead use second prey cells to complete their life cycle.IMPORTANCE New strategies are needed to combat multidrug-resistant bacterial infections. Application of the predatory bacterium Bdellovibrio bacteriovorus, which kills other bacteria, including pathogens, is considered promising for combating bacterial infections. The B. bacteriovorus life cycle consists of two phases, a free-living, invasive attack phase and an intracellular reproductive phase, in which this predatory bacterium degrades the host's macromolecules and reuses them for its own growth. To understand the use of B. bacteriovorus as a "living antibiotic," it is first necessary to dissect its life cycle, including chromosome replication. Here, we present a real-time investigation into subcellular localization of chromosome replication in a single cell of B. bacteriovorus This process initiates at the invasion pole of B. bacteriovorus and proceeds until several copies of the chromosome have been completely synthesized. Interestingly, we demonstrate that some cells of B. bacteriovorus require two prey cells sequentially to complete their life cycle.

Evaluation of Predation Capability of Periodontopathogens Bacteria by Bdellovibrio Bacteriovorus HD100. An in Vitro Study.

Treatment options against periodontitis attempt to completely remove oral microbiota even if several species in dental plaque demonstrate protective features. Predatory bacteria that selectively predate solely on Gram-negative bacteria might be a viable therapeutic alternative. Therefore, the aim of this study is to in vitro evaluate the susceptibility of some oral pathogens to predation by B. bacteriovorus HD100 in liquid suspension. Cultures of prey cell were prepared in brain heart infusion broth (BHI) broth incubating overnight at the appropriate conditions for each organism to reach log phase of growth. Predatory activity was assessed by measuring optical density at 600 nm after 12, 24, 48 and 72 hours. Statistical analysis was performed using the Mann–Whitney U test and p values less than 0.05 were considered statistically significant. The study demonstrated that B. bacteriovorus is able to predate on aerobic species and on microaerophilic ones (p < 0.05) but also that its predatory capacity is strongly compromised by the conditions of anaerobiosis. B. bacteriovorus, in fact, was unable to predate the anaerobic species involved in the present study (F. nucleatum and P. gingivalis). The findings of the study suggest that B. bacteriovorus is able to tolerate microaerophilic conditions and that in anaerobiosis it cannot exert its predatory capacity. Such evidence could lead to its use as an agent to prevent recolonization of the periodontal pocket following therapy. Further studies are needed to investigate the activity of B. bacteriovorus against recently recognized periodontopathogens, alone or organized in biofilms of multi-species communities.

Multi-omics characterization of the necrotrophic mycoparasite Saccharomycopsis schoenii.

Pathogenic yeasts and fungi are an increasing global healthcare burden, but discovery of novel antifungal agents is slow. The mycoparasitic yeast Saccharomycopsis schoenii was recently demonstrated to be able to kill the emerging multi-drug resistant yeast pathogen Candida auris. However, the molecular mechanisms involved in the predatory activity of S. schoenii have not been explored. To this end, we de novo sequenced, assembled and annotated a draft genome of S. schoenii. Using proteomics, we confirmed that Saccharomycopsis yeasts have reassigned the CTG codon and translate CTG into serine instead of leucine. Further, we confirmed an absence of all genes from the sulfate assimilation pathway in the genome of S. schoenii, and detected the expansion of several gene families, including aspartic proteases. Using Saccharomyces cerevisiae as a model prey cell, we honed in on the timing and nutritional conditions under which S. schoenii kills prey cells. We found that a general nutrition limitation, not a specific methionine deficiency, triggered predatory activity. Nevertheless, by means of genome-wide transcriptome analysis we observed dramatic responses to methionine deprivation, which were alleviated when S. cerevisiae was available as prey, and therefore postulate that S. schoenii acquired methionine from its prey cells. During predation, both proteomic and transcriptomic analyses revealed that S. schoenii highly upregulated and translated aspartic protease genes, probably used to break down prey cell walls. With these fundamental insights into the predatory behavior of S. schoenii, we open up for further exploitation of this yeast as a biocontrol yeast and/or source for novel antifungal agents.