Going against the grain: chemotaxis and infection in Vibrio cholerae

Advancements in bacterial chemotaxis: Utilizing the navigational intelligence of bacteria and its practical applications

The fascinating world of microscopic life unveils a captivating spectacle as bacteria effortlessly maneuver through their surroundings with astonishing accuracy, guided by the intricate mechanism of chemotaxis. This review explores the complex mechanisms behind this behavior, analyzing the flagellum as the driving force and unraveling the intricate signaling pathways that govern its movement. We delve into the hidden costs and benefits of this intricate skill, analyzing its potential to propagate antibiotic resistance gene while shedding light on its vital role in plant colonization and beneficial symbiosis. We explore the realm of human intervention, considering strategies to manipulate bacterial chemotaxis for various applications, including nutrient cycling, algal bloom and biofilm formation. This review explores the wide range of applications for bacterial capabilities, from targeted drug delivery in medicine to bioremediation and disease control in the environment. Ultimately, through unraveling the intricacies of bacterial movement, we can enhance our comprehension of the intricate web of life on our planet. This knowledge opens up avenues for progress in fields such as medicine, agriculture, and environmental conservation.

Is ageing undesirable? An ethical analysis

The technical possibilities of biomedicine open up the opportunity to intervene in ageing itself with the aim of mitigating, reducing or eliminating it. However, before undertaking these changes or rejecting them outright, it is necessary to ask ourselves if what would be lost by doing so really has much value. This article will analyse the desirability of ageing from an individual point of view, without circumscribing this question to the desirability or undesirability of death. First, we will present the three most widely used arguments to reject biomedical interventions against ageing. We will argue that only the last of these arguments provides a consistent answer to the question of the desirability of ageing. Second, we will show that the third argument falls prey to a conceptual confusion that we will call the paradox of ageing: although ageing entails negative health effects, it leads to a life stage with valuable goods. Both valuations, one positive and the other negative, refer to two different dimensions of ageing: the chronological and the biological. We will defend that, by not adequately distinguishing these two types of ageing, it does not become apparent that all the valuable goods exclusive to ageing derive only from its chronological dimension. Third, we will argue that, if we just conceive ageing biologically, it is undesirable. We will elaborate on the two kinds of undesirable effects biological ageing has: direct and indirect. Finally, we will respond to potential objections by adducing that these are insufficient to weaken our argument.

Vibrio cholerae virulence and its suppression through the quorum-sensing system

Vibrio cholerae is a cholera-causing pathogen known to instigate severe contagious diarrhea that affects millions globally. Survival of vibrios depend on a combination of multicellular responses and adapt to changes that prevail in the environment. This process is achieved through a strong communication at the cellular level, the process has been recognized as quorum sensing (QS). The severity of infection is highly dependent on the QS of vibrios in the gut milieu. The quorum may exist in a low/high cell density (LCD/HCD) state to exert a positive or negative response to control the regulatory pathogenic networks. The impact of this regulation reflects on the transition of pathogenic V. cholerae from the environment to infect humans and cause outbreaks or epidemics of cholera. In this context, the review portrays various regulatory processes and associated virulent pathways, which maneuver and control LCD and HCD states for their survival in the host. Although several treatment options are existing, promotion of therapeutics by exploiting the virulence network may potentiate ineffective antibiotics to manage cholera. In addition, this approach is also useful in resource-limited settings, where the accessibility to antibiotics or conventional therapeutic options is limited.

The implication of viability and pathogenicity by truncated lipopolysaccharide in Yersinia enterocolitica

The fast envelope stress responses play a key role in the transmission and pathogenesis of Yersinia enterocolitica, one of the most common foodborne pathogens. Our previous study showed that deletion of the waaF gene, essential for the biosynthesis of lipopolysaccharide (LPS) core polysaccharides, led to the formation of a truncated LPS structure and induced cell envelope stress. This envelope stress may disturb the intracellular signal transduction, thereby affecting the physiological functions of Y. enterocolitica. In this study, truncated LPS caused by waaF deletion was used as a model of envelope stress in Y. enterocolitica. We investigated the mechanisms of envelope stress responses and the cellular functions affected by truncated LPS. Transcriptome analysis and phenotypic validation showed that LPS truncation reduced flagellar assembly, bacterial chemotaxis, and inositol phosphate metabolism, presenting lower pathogenicity and viability both in vivo and in vitro environments. Further 4D label-free phosphorylation analysis confirmed that truncated LPS perturbed multiple intracellular signal transduction pathways. Specifically, a comprehensive discussion was conducted on the mechanisms by which chemotactic signal transduction and Rcs system contribute to the inhibition of chemotaxis. Finally, the pathogenicity of Y. enterocolitica with truncated LPS was evaluated in vitro using IPEC-J2 cells as models, and it was found that truncated LPS exhibited reduced adhesion, invasion, and toxicity of Y. enterocolitica to IPEC-J2 cells. Our research provides an understanding of LPS in the regulation of Y. enterocolitica viability and pathogenicity and, thus, opening new avenues to develop novel food safety strategies or drugs to prevent and control Y. enterocolitica infections. KEY POINTS: • Truncated LPS reduces flagellar assembly, chemotaxis, and inositol phosphate metabolism in Y. enterocolitica. • Truncated LPS reduces adhesion, invasion, and toxicity of Y. enterocolitica to IPEC-J2 cells. • Truncated LPS regulates intracellular signal transduction of Y. enterocolitica.

Cross-Platform Transcriptomic Data Integration, Profiling, and Mining in Vibrio cholerae

A large number of transcriptome studies generate important data and information for the study of pathogenic mechanisms of pathogens, including Vibrio cholerae. V. cholerae transcriptome data include RNA-seq and microarray: microarray data mainly include clinical human and environmental samples, and RNA-seq data mainly focus on laboratory processing conditions, including different stresses and experimental animals in vivo. In this study, we integrated the data sets of both platforms using Rank-in and the Limma R package normalized Between Arrays function, achieving the first cross-platform transcriptome data integration of V. cholerae. By integrating the entire transcriptome data, we obtained the profiles of the most active or silent genes. By transferring the integrated expression profiles into the weighted correlation network analysis (WGCNA) pipeline, we identified the important functional modules of V. cholerae in vitro stress treatment, gene manipulation, and in vitro culture as DNA transposon, chemotaxis and signaling, signal transduction, and secondary metabolic pathways, respectively. The analysis of functional module hub genes revealed the uniqueness of clinical human samples; however, under specific expression patterning, the Δhns, ΔoxyR1 strains, and tobramycin treatment group showed high expression profile similarity with human samples. By constructing a protein-protein interaction (PPI) interaction network, we discovered several unreported novel protein interactions within transposon functional modules. IMPORTANCE We used two techniques to integrate RNA-seq data for laboratory studies with clinical microarray data for the first time. The interactions between V. cholerae genes were obtained from a global perspective, as well as comparing the similarity between clinical human samples and the current experimental conditions, and uncovering the functional modules that play a major role under different conditions. We believe that this data integration can provide us with some insight and basis for elucidating the pathogenesis and clinical control of V. cholerae.

Advances in cholera research: from molecular biology to public health initiatives

The aquatic bacterium Vibrio cholerae is the etiological agent of the diarrheal disease cholera, which has plagued the world for centuries. This pathogen has been the subject of studies in a vast array of fields, from molecular biology to animal models for virulence activity to epidemiological disease transmission modeling. V. cholerae genetics and the activity of virulence genes determine the pathogenic potential of different strains, as well as provide a model for genomic evolution in the natural environment. While animal models for V. cholerae infection have been used for decades, recent advances in this area provide a well-rounded picture of nearly all aspects of V. cholerae interaction with both mammalian and non-mammalian hosts, encompassing colonization dynamics, pathogenesis, immunological responses, and transmission to naïve populations. Microbiome studies have become increasingly common as access and affordability of sequencing has improved, and these studies have revealed key factors in V. cholerae communication and competition with members of the gut microbiota. Despite a wealth of knowledge surrounding V. cholerae, the pathogen remains endemic in numerous countries and causes sporadic outbreaks elsewhere. Public health initiatives aim to prevent cholera outbreaks and provide prompt, effective relief in cases where prevention is not feasible. In this review, we describe recent advancements in cholera research in these areas to provide a more complete illustration of V. cholerae evolution as a microbe and significant global health threat, as well as how researchers are working to improve understanding and minimize impact of this pathogen on vulnerable populations.

Vibrio cholerae, classification, pathogenesis, immune response, and trends in vaccine development

Vibrio cholerae is the causative agent of cholera, a highly contagious diarrheal disease affecting millions worldwide each year. Cholera is a major public health problem, primarily in countries with poor sanitary conditions and regions affected by natural disasters, where access to safe drinking water is limited. In this narrative review, we aim to summarize the current understanding of the evolution of virulence and pathogenesis of V. cholerae as well as provide an overview of the immune response against this pathogen. We highlight that V. cholerae has a remarkable ability to adapt and evolve, which is a global concern because it increases the risk of cholera outbreaks and the spread of the disease to new regions, making its control even more challenging. Furthermore, we show that this pathogen expresses several virulence factors enabling it to efficiently colonize the human intestine and cause cholera. A cumulative body of work also shows that V. cholerae infection triggers an inflammatory response that influences the development of immune memory against cholera. Lastly, we reviewed the status of licensed cholera vaccines, those undergoing clinical evaluation, and recent progress in developing next-generation vaccines. This review offers a comprehensive view of V. cholerae and identifies knowledge gaps that must be addressed to develop more effective cholera vaccines.

Analysis of CheW-like domains provides insights into organization of prokaryotic chemotaxis systems

The ability to control locomotion in a dynamic environment provides a competitive advantage for microorganisms, thus driving the evolution of sophisticated regulatory systems. In total, 19 known categories of chemotaxis systems control motility mediated by flagella or Type IV pili, plus other cellular functions. A key feature that distinguishes chemotaxis systems from generic two-component regulatory systems is separation of receptor and kinase functions into distinct proteins, linked by CheW scaffold proteins. This arrangement allows for formation of varied arrays with remarkable signaling properties. We recently analyzed sequences of CheW-like domains found in CheA kinases and CheW and CheV scaffold proteins. In total, 16 Architectures of CheA, CheW, and CheV proteins contain ~94% of all CheW-like domains and form six Classes with likely functional specializations. We surveyed chemotaxis system categories and proteins containing CheW-like domains in ~1900 prokaryotic species, the most comprehensive analysis to date, revealing new insights. Co-occurrence analyses suggested that many chemotaxis systems occur in non-random combinations within species, implying synergy or antagonism. Furthermore, many Architectures of proteins containing CheW-like domains occurred predominantly with specific categories of chemotaxis systems, suggesting specialized functional interactions. We propose Class 1 (~80%) and Class 6 (~20%) CheW proteins exhibit preferences for distinct chemoreceptor structures. Furthermore, rare (~1%) Class 2 CheW proteins frequently co-occurred with methyl-accepting coiled coil proteins, which contain both receptor and kinase functions and so do not require connection via a CheW scaffold but may benefit from arrays. Last, rare multidomain CheW proteins may interact with different receptors than single-domain CheW proteins.

Motility Control as a Possible Link Between Quorum Sensing to Surface Attachment in Vibrio Species

In this chapter, we discuss motility control as a possible link between quorum sensing (QS) to surface attachment in Vibrio species. QS regulates a variety of behaviors that are important for the life cycle of many bacterial species, including virulence factor production, biofilm formation, or metabolic homeostasis. Therefore, without QS, many species of bacteria cannot survive in their natural environments. Here, we summarize several QS systems in different Vibrio species and discuss some of emerging features that suggest QS is intimately connected to motility control. Finally, we speculate the connection between motility and QS is critical for Vibrio species to detect solid surfaces for surface attachment.

Telomerase reactivation induces progression of mouse Braf V600E -driven thyroid cancers without telomere lengthening

Mutations in the promoter of the telomerase reverse transcriptase ( TERT ) gene are the paradigm of a cross-cancer alteration in a non-coding region. TERT promoter mutations (TPMs) are biomarkers of poor prognosis in several tumors, including thyroid cancers. TPMs enhance TERT transcription, which is otherwise silenced in adult tissues, thus reactivating a bona fide oncoprotein. To study TERT deregulation and its downstream consequences, we generated a Tert mutant promoter mouse model via CRISPR/Cas9 engineering of the murine equivalent locus (Tert -123C>T ) and crossed it with thyroid-specific Braf V600E -mutant mice. We also employed an alternative model of Tert overexpression (K5-Tert). Whereas all Braf V600E animals developed well-differentiated papillary thyroid tumors, 29% and 36% of Braf V600E +Tert -123C>T and Braf V600E +K5-Tert mice progressed to poorly differentiated thyroid cancers at week 20, respectively. Braf+Tert tumors showed increased mitosis and necrosis in areas of solid growth, and older animals from these cohorts displayed anaplastic-like features, i.e., spindle cells and macrophage infiltration. Murine Tert promoter mutation increased Tert transcription in vitro and in vivo , but temporal and intra-tumoral heterogeneity was observed. RNA-sequencing of thyroid tumor cells showed that processes other than the canonical Tert-mediated telomere maintenance role operate in these specimens. Pathway analysis showed that MAPK and PI3K/AKT signaling, as well as processes not previously associated with this tumor etiology, involving cytokine and chemokine signaling, were overactivated. Braf+Tert animals remained responsive to MAPK pathway inhibitors. These models constitute useful pre-clinical tools to understand the cell-autonomous and microenvironment-related consequences of Tert-mediated progression in advanced thyroid cancers and other aggressive tumors carrying TPMs.

Development of a smart pH-responsive nano-polymer drug, 2-methoxy-4-vinylphenol conjugate against the intestinal pathogen, Vibrio cholerae

Vibrio cholerae causes cholera, an acute diarrhoeal disease. The virulence in V. cholerae is regulated by the quorum-sensing mechanism and response regulator LuxO positively regulates the expression of virulence determinants adhesion, biofilm formation, and cholera toxin production. Previous in-silico studies revealed that 2-methoxy-4-vinylphenol could bind to the ATP binding site of LuxO and the complex was compact and stable in pHs like intestinal pHs. Here, we have explored the polymeric nano-formulation of 2-methoxy-4-vinylphenol using cellulose acetate phthalate for controlled drug release and their effectiveness in attenuating the expression of V. cholerae virulence. Physico-chemical characterization of the formulation showed particles with a mean size of 91.8 ± 14 nm diameter and surface charge of - 14.7 ± 0.07 mV. The uniform round polymeric nanoparticles formed displayed about 51% burst release of the drug at pH 7 by 3rd h, followed by a controlled linear release in alkaline pH. The polymeric nanoparticles demonstrated a tenfold increase in intestinal membrane permeability ex-vivo. At lower concentrations, the 2-methoxy-4-vinylphenol polymeric nanoparticles were non-cytotoxic to Int 407 cells. In-vitro analysis at pH 6, pH 7, pH 8, and pH 9 revealed that cellulose acetate phthalate-2-methoxy-4-vinylphenol nanoparticles were non-bactericidal at concentrations up to 500 μg/mL. At 31.25 μg/mL, the nanoparticles inhibited about 50% of the biofilm formation of V. cholerae MTCC 3905 and HYR14 strains. At this concentration, the adherence of V. cholerae MTCC 3905 and HYR14 to Int 407 cell lines were also significantly affected. Gene expression analysis revealed that the expression of tcp, qrr, and ct at pH 6, 7, 8, and 9 has reduced. The CAP-2M4VP nanoparticles have demonstrated the potential to effectively reduce the virulence of V. cholerae in-vitro.

DegS protease regulates the motility, chemotaxis, and colonization of Vibrio cholerae

In bacteria, DegS protease functions as an activating factor of the σ^E envelope stress response system, which ultimately activates the transcription of stress response genes in the cytoplasm. On the basis of high-throughput RNA sequencing, we have previously found that degS knockout inhibits the expression of flagellum synthesis- and chemotaxis-related genes, thereby indicating that DegS may be involved in the regulation of V. cholerae motility. In this study, we examined the relationships between DegS and motility in V. cholerae. Swimming motility and chemotaxis assays revealed that degS or rpoE deletion promotes a substantial reduction in the motility and chemotaxis of V. cholerae, whereas these activities were restored in ΔdegS::degS and ΔdegSΔrseA strains, indicating that DegS is partially dependent on σ^E to positively regulate V. cholerae activity. Gene-act network analysis revealed that the cAMP-CRP-RpoS signaling pathway, which plays an important role in flagellar synthesis, is significantly inhibited in ΔdegS mutants, whereas in response to the overexpression of cyaA/crp and rpoS in the ΔdegS strain, the motility and chemotaxis of the ΔdegS + cyaA/crp and ΔdegS + rpoS strains were partially restored compared with the ΔdegS strain. We further demonstrated that transcription levels of the flagellar regulatory gene flhF are regulated by DegS via the cAMP-CRP-RpoS signaling pathway. Overexpression of the flhF gene in the ΔdegS strain partially restored motility and chemotaxis. In addition, suckling mouse intestinal colonization experiments indicated that the ΔdegS and ΔrpoE strains were characterized by the poor colonization of mouse intestines, whereas colonization efficacy was restored in the ΔdegSΔrseA, ΔdegS + cyaA/crp, ΔdegS + rpoS, and ΔdegS + flhF strains. Collectively, our findings indicate that DegS regulates the motility and chemotaxis of V. cholerae via the cAMP-CRP-RpoS-FlhF pathway, thereby influencing the colonization of suckling mouse intestines.

Immunization with a bicistronic DNA vaccine modulates systemic IFN-γ and IL-10 expression against Vibrio cholerae infection

Introduction. Cholera is an acute enteric infection caused by Vibrio cholerae, particularly in areas lacking access to clean water. Despite the global effort to improve water quality in these regions, the burden of cholera in recent years has not yet declined. Interest has therefore extended in the use of bicistronic DNA vaccine encoding ctxB and tcpA genes of V. cholerae as a potential vaccine.Hypothesis/Gap Statement. The potential of a bicistronic DNA vaccine, pVAX-ctxB-tcpA has not been determined in vitro and in vivo.Aim. The goal of present study was to evaluate in vitro expression and in vivo potential of pVAX-ctxB-tcpA vaccine against V. cholerae.Methodology. The pVAX-ctxB-tcpA was transiently transfected into mammalian COS-7 cells, and the in vitro expression was assessed using fluorescence and Western blot analyses. Next, the vaccine was encapsulated into sodium alginate using water-in-oil emulsification and evaluated for its efficiency in different pH conditions. Subsequently, oral vaccination using en(pVAX-ctxB-tcpA) was performed in vivo. The animals were challenged with V. cholerae O1 El Tor after 2 weeks of vaccination using the Removable Intestinal Tie-Adult Rabbit Diarrhoea (RITARD) model. Following the infection challenge, the rabbits were monitored for evidence of symptoms, and analysed for systemic cytokine expression level (TNF-α, IFN-γ, IL-6 and IL-10) using quantitative real-time polymerase chain reaction.Results. The in vitro expression of pVAX-ctxB-tcpA was successfully verified via fluorescence and Western blot analyses. Meanwhile, in vivo analysis demonstrated that the en(pVAX-ctxB-tcpA) was able to protect the RITARD model against V. cholerae infection due to a lack of evidence on the clinical manifestations of cholera following bacterial challenge. Furthermore, the bicistronic group showed an upregulation of systemic IFN-γ and IL-10 following 12 days of vaccination, though not significant, suggesting the possible activation of both T-helper 1 and 2 types of response. However, upon bacterial challenge, the gene expression of all cytokines did not change.Conclusion. Our findings suggest that the bicistronic plasmid DNA vaccine, pVAX-ctxB-tcpA, showed a potential role in inducing immune response against cholera through upregulation of in vitro gene and protein expression as well as in vivo cytokine gene expression, particularly IFN-γ and IL-10.

Collective responses of bacteria to a local source of conflicting effectors

To cope in complex environments, motile bacteria have developed a chemosensory system that integrates multiple cues and directs their motion toward regions that it deems favorable. However, we have a limited understanding of the principles that govern bacterial behavior in complex stimuli fields. Here, we followed the spatial redistribution of E. coli cells in perplexing environments created by a local source of both beneficial (nutrients) and hazardous (low pH or indole) effectors. We identified two fundamentally distinct collective responses: a ‘trade-off’ response, in which bacteria sharply accumulated at a distance from the source that reflected a trade-off between the propagating effectors, and a ‘bet-hedging’ response, in which part of the bacteria accumulated away from the source, avoiding the hazardous effector, while the other part evaded the repulsive force and accumulated at the source. In addition, we demonstrate that cells lacking the Tsr sensor swim toward both repellents and, surprisingly, even toward pH values well below 7. Using a numerical analysis, we could correlate the collective bacterial responses with fundamentally distinct chemotactic force fields created along the channel by the propagation of the effectors and their unique perception by the chemosensory system.

Achievements in bacterial flagellar research with focus on Vibrio species

In 1980's, the most genes involved in the bacterial flagellar function and formation had been isolated though many of their functions or roles were not clarified. Bacterial flagella are the primary locomotive organ and are not necessary for growing in vitro but are probably essential for living in natural condition and are involved in the pathogenicity. In vitro, the flagella-deficient strains can grow at rates similar to wild-type strains. More than 50 genes are responsible for flagellar function, and the flagellum is constructed by more than 20 structural proteins. The maintenance cost of flagellum is high as several genes are required for its development. The fact that it evolved as a motor organ even with such the high cost shows that the motility is indispensable to survive under the harsh environment of Earth. In this review, we focus on flagella-related research conducted by the authors for about 40 years and flagellar research focused on Vibrio spp. This article is protected by copyright. All rights reserved.

Effect of inoculum size and antibiotics on bacterial traveling bands in a thin microchannel defined by optical adhesive

Phenotypic diversity in bacterial flagella-induced motility leads to complex collective swimming patterns, appearing as traveling bands with transient locally enhanced cell densities. Traveling bands are known to be a bacterial chemotactic response to self-generated nutrient gradients during growth in resource-limited microenvironments. In this work, we studied different parameters of Escherichia coli (E. coli) collective migration, in particular the quantity of bacteria introduced initially in a microfluidic chip (inoculum size) and their exposure to antibiotics (ampicillin, ciprofloxacin, and gentamicin). We developed a hybrid polymer-glass chip with an intermediate optical adhesive layer featuring the microfluidic channel, enabling high-content imaging of the migration dynamics in a single bacterial layer, i.e., bacteria are confined in a quasi-2D space that is fully observable with a high-magnification microscope objective. On-chip bacterial motility and traveling band analysis was performed based on individual bacterial trajectories by means of custom-developed algorithms. Quantifications of swimming speed, tumble bias and effective diffusion properties allowed the assessment of phenotypic heterogeneity, resulting in variations in transient cell density distributions and swimming performance. We found that incubation of isogeneic E. coli with different inoculum sizes eventually generated different swimming phenotype distributions. Interestingly, incubation with antimicrobials promoted bacterial chemotaxis in specific cases, despite growth inhibition. Moreover, E. coli filamentation in the presence of antibiotics was assessed, and the impact on motility was evaluated. We propose that the observation of traveling bands can be explored as an alternative for fast antimicrobial susceptibility testing.

Polyunsaturated fatty acids cause physiological and behavioral changes in Vibrio alginolyticus and Vibrio fischeri

Vibrio alginolyticus and Vibrio (Aliivibrio) fischeri are Gram-negative bacteria found globally in marine environments. During the past decade, studies have shown that certain Gram-negative bacteria, including Vibrio species (cholerae, parahaemolyticus, and vulnificus) are capable of using exogenous polyunsaturated fatty acids (PUFAs) to modify the phospholipids of their membrane. Moreover, exposure to exogenous PUFAs has been shown to affect certain phenotypes that are important factors of virulence. The purpose of this study was to investigate whether V. alginolyticus and V. fischeri are capable of responding to exogenous PUFAs by remodeling their membrane phospholipids and/or altering behaviors associated with virulence. Thin-layer chromatography (TLC) analyses and ultra-performance liquid chromatography-electrospray ionization mass spectrometry (UPLC/ESI-MS) confirmed incorporation of all PUFAs into membrane phosphatidylglycerol and phosphatidylethanolamine. Several growth phenotypes were identified when individual fatty acids were supplied in minimal media and as sole carbon sources. Interestingly, several PUFAs acids inhibited growth of V. fischeri. Significant alterations to membrane permeability were observed depending on fatty acid supplemented. Strikingly, arachidonic acid (20:4) reduced membrane permeability by approximately 35% in both V. alginolyticus and V. fischeri. Biofilm assays indicated that fatty acid influence was dependent on media composition and temperature. All fatty acids caused decreased swimming motility in V. alginolyticus, while only linoleic acid (18:2) significantly increased swimming motility in V. fischeri. In summary, exogenous fatty acids cause a variety of changes in V. alginolyticus and V. fischeri, thus adding these bacteria to a growing list of Gram-negatives that exhibit versatility in fatty acid utilization and highlighting the potential for environmental PUFAs to influence phenotypes associated with planktonic, beneficial, and pathogenic associations.

Vibrio cholerae motility in aquatic and mucus-mimicking environments

Cholera disease is caused by Vibrio cholerae infecting the lining of the small intestine and results in severe diarrhea. V. cholerae’s swimming motility is known to play a crucial role in pathogenicity and may aid the bacteria in crossing the intestinal mucus barrier to reach sites of infection, but the exact mechanisms are unknown. The cell can be either pushed or pulled by its single polar flagellum, but there is no consensus on the resulting repertoire of motility behaviors. We use high-throughput three-dimensional (3D) bacterial tracking to observe V. cholerae swimming in buffer, in viscous solutions of the synthetic polymer PVP, and in mucin solutions that may mimic the host environment. We perform a statistical characterization of its motility behavior on the basis of large 3D trajectory data sets. We find that V. cholerae performs asymmetric run-reverse-flick motility, consisting of a sequence of a forward run, reversal, and a shorter backward run, followed by a turn by approximately 90°, called a flick, preceding the next forward run. Unlike many run-reverse-flick swimmers, V. cholerae’s backward runs are much shorter than its forward runs, resulting in an increased effective diffusivity. We also find that the swimming speed is not constant but subject to frequent decreases. The turning frequency in mucin matches that observed in buffer. Run-reverse-flick motility and speed fluctuations are present in all environments studied, suggesting that these behaviors also occur in natural aquatic habitats as well as the host environment.

IMPORTANCE Cholera disease produces vomiting and severe diarrhea and causes approximately 100,000 deaths per year worldwide. The disease is caused by the bacterium Vibrio cholerae colonizing the lining of the small intestine. V. cholerae’s ability to swim is known to increase its infectivity, but the underlying mechanisms are not known. One possibility is that swimming aids in crossing the protective mucus barrier that covers the lining of the small intestine. Our work characterizing how V. cholerae swims in environments that mimic properties of the host environment may advance the understanding of how motility contributes to infection.

Vibrio cholerae's mysterious Seventh Pandemic island (VSP-II) encodes novel Zur-regulated zinc starvation genes involved in chemotaxis and cell congregation

Vibrio cholerae is the causative agent of cholera, a notorious diarrheal disease that is typically transmitted via contaminated drinking water. The current pandemic agent, the El Tor biotype, has undergone several genetic changes that include horizontal acquisition of two genomic islands (VSP-I and VSP-II). VSP presence strongly correlates with pandemicity; however, the contribution of these islands to V. cholerae's life cycle, particularly the 26-kb VSP-II, remains poorly understood. VSP-II-encoded genes are not expressed under standard laboratory conditions, suggesting that their induction requires an unknown signal from the host or environment. One signal that bacteria encounter under both host and environmental conditions is metal limitation. While studying V. cholerae's zinc-starvation response in vitro, we noticed that a mutant constitutively expressing zinc starvation genes (Δzur) congregates at the bottom of a culture tube when grown in a nutrient-poor medium. Using transposon mutagenesis, we found that flagellar motility, chemotaxis, and VSP-II encoded genes were required for congregation. The VSP-II genes encode an AraC-like transcriptional activator (VerA) and a methyl-accepting chemotaxis protein (AerB). Using RNA-seq and lacZ transcriptional reporters, we show that VerA is a novel Zur target and an activator of the nearby AerB chemoreceptor. AerB interfaces with the chemotaxis system to drive oxygen-dependent congregation and energy taxis. Importantly, this work suggests a functional link between VSP-II, zinc-starved environments, and energy taxis, yielding insights into the role of VSP-II in a metal-limited host or aquatic reservoir.

Microscale tracking of coral-vibrio interactions

To improve our understanding of coral infection and disease, it is important to study host-pathogen interactions at relevant spatio-temporal scales. Here, we provide a dynamic microscopic view of the interaction between a coral pathogen, Vibrio coralliilyticus and its coral host Pocillopora damicornis. This was achieved using a microfluidics-based system facilitating control over flow, light and temperature conditions. Combined with time-resolved biochemical and microbial analyses of the system exudates, this approach provides novel insights into the early phases of a coral infection at unprecedented spatio-temporal resolution. We provide evidence that infection may occur through ingestion of the pathogen by the coral polyps, or following pathogen colonization of small tissue lesions on the coral surface. Pathogen ingestion invariably induced the release of pathogen-laden mucus from the gastrovascular cavity. Despite the high bacterial load used in our experiments, approximately one-third of coral fragments tested did not develop further symptoms. In the remaining two-thirds, mucus spewing was followed by the severing of calicoblastic connective tissues (coenosarc) and subsequently necrosis of most polyps. Despite extensive damage to symptomatic colonies, we frequently observed survival of individual polyps, often accompanied by polyp bail-out. Biochemical and microbial analyses of exudates over the course of symptomatic infections revealed that severing of the coenosarc was followed by an increase in matrix metaloprotease activity, and subsequent increase in both pathogen and total bacterial counts. Combined, these observations provide a detailed description of a coral infection, bringing us a step closer to elucidating the complex interactions underlying coral disease.

Chemotactic invasion in deep soft tissue by Vibrio vulnificus is essential for the progression of necrotic lesions

Necrotizing soft tissue infections (NSTI) progress to severe necrosis and result in fatal sepsis within a short time. Vibrio vulnificus is a causative agent and can spread from the initial infection site through soft tissue finally to the systemic circulation of the host. The motility and chemotaxis of this bacterium are essential for proliferation and lethality in a murine model of the infection, but their role in pathogenicity has not been characterized. In this study, we revealed the roles of motility and chemotaxis during the process of V. vulnificus infection. We compared a nonmotile mutant and two nonchemotactic mutants with their parent strain (WT) with regard to bacterial spread using an in vivo imaging system (IVIS) and invasion by detection of bacteria from the muscle and spleen of a murine infection model. WT rapidly spread throughout the infected thigh and invaded deep muscle causing severe tissue damage. The detection rate in the systemic circulation and the lethality were high. On the other hand, the nonmotile mutant stayed at the inoculation site, and the nonchemotactic mutants spread only slowly through the soft tissue of the infected thigh. Detection in the systemic circulation, the degree of tissue damage, and the lethality of nonchemotactic mutants were significantly reduced in mice compared with WT. This study demonstrated that chemotaxis is essential for invasion from the infection site to the deep and distant tissues and the main pathogenic factor for the rapid progression leading to sepsis in V. vulnificus NSTI.

Regulatory Effects of CsrA in Vibrio cholerae

Vibrio cholerae, a Gram-negative bacterium, is a natural inhabitant of the aqueous environment. However, once ingested, this bacterium can colonize the human host and cause the disease cholera.

CsrA is a posttranscriptional global regulator in Vibrio cholerae. Although CsrA is critical for V. cholerae survival within the mammalian host, the regulatory targets of CsrA remain mostly unknown. To identify pathways controlled by CsrA, RNA-seq transcriptome analysis was carried out by comparing the wild type and the csrA mutant grown to early exponential, mid-exponential, and stationary phases of growth. This enabled us to identify the global effects of CsrA-mediated regulation throughout the V. cholerae growth cycle. We found that CsrA regulates 22% of the V. cholerae transcriptome, with significant regulation within the gene ontology (GO) processes that involve amino acid transport and metabolism, central carbon metabolism, lipid metabolism, iron uptake, and flagellum-dependent motility. Through CsrA-RNA coimmunoprecipitation experiments, we found that CsrA binds to multiple mRNAs that encode regulatory proteins. These include transcripts encoding the major sigma factors RpoS and RpoE, which may explain how CsrA regulation affects such a large proportion of the V. cholerae transcriptome. Other direct targets include flrC, encoding a central regulator in flagellar gene expression, and aphA, encoding the virulence gene transcription factor AphA. We found that CsrA binds to the aphA mRNA both in vivo and in vitro, and CsrA significantly increases AphA protein synthesis. The increase in AphA was due to increased translation, not transcription, in the presence of CsrA, consistent with CsrA binding to the aphA transcript and enhancing its translation. CsrA is required for the virulence of V. cholerae and this study illustrates the central role of CsrA in virulence gene regulation.

[Flagellar related genes and functions in Vibrio]

Bacteria can move or swim by flagella. On the other hand, the motile ability is not necessary to live at all. In laboratory, the flagella-deficient strains can grow just like the wild-type strains. The flagellum is assembled from more than 20 structural proteins and there are more than 50 genes including the structural genes to regulate or support the flagellar formation. The cost to construct the flagellum is so expensive. The fact that it evolved as a motor organ means even at such the large cost shows that the flagellum is essential for survival in natural condition. In this review, we would like to focus on the flagella-related researches conducted by the authors and the flagellar research on Vibrio spp.

2D vs 3D tracking in bacterial motility analysis

<abstract> <p>Digital holographic microscopy provides the ability to observe throughout a large volume without refocusing. This capability enables simultaneous observations of large numbers of microorganisms swimming in an essentially unconstrained fashion. However, computational tools for tracking large 4D datasets remain lacking. In this paper, we examine the errors introduced by tracking bacterial motion as 2D projections vs. 3D volumes under different circumstances: bacteria free in liquid media and bacteria near a glass surface. We find that while XYZ speeds are generally equal to or larger than XY speeds, they are still within empirical uncertainties. Additionally, when studying dynamic surface behavior, the Z coordinate cannot be neglected.</p> </abstract>

Identification of signaling pathways, matrix-digestion enzymes, and motility components controlling Vibrio cholerae biofilm dispersal

The global pathogen Vibrio cholerae alternates between free swimming and existing in sessile multicellular communities known as biofilms. Transitioning between these lifestyles is key for disease transmission. V. cholerae biofilm formation is well studied; however, almost nothing is known about how V. cholerae cells disperse from biofilms, precluding our understanding of a central pathogenicity step. Here, we conducted an imaging screen for V. cholerae mutants that failed to disperse. Our screen revealed three classes of components required for dispersal: signal transduction, matrix degradation, and motility factors. We characterized these components to reveal the sequence of molecular events that choreograph V. cholerae biofilm dispersal. Our report provides a framework for developing strategies to modulate biofilm dispersal to prevent or treat disease.

Bacteria alternate between being free-swimming and existing as members of sessile multicellular communities called biofilms. The biofilm lifecycle occurs in three stages: cell attachment, biofilm maturation, and biofilm dispersal. Vibrio cholerae biofilms are hyperinfectious, and biofilm formation and dispersal are considered central to disease transmission. While biofilm formation is well studied, almost nothing is known about biofilm dispersal. Here, we conducted an imaging screen for V. cholerae mutants that fail to disperse, revealing three classes of dispersal components: signal transduction proteins, matrix-degradation enzymes, and motility factors. Signaling proteins dominated the screen and among them, we focused on an uncharacterized two-component sensory system that we term DbfS/DbfR for dispersal of biofilm sensor/regulator. Phospho-DbfR represses biofilm dispersal. DbfS dephosphorylates and thereby inactivates DbfR, which permits dispersal. Matrix degradation requires two enzymes: LapG, which cleaves adhesins, and RbmB, which digests matrix polysaccharides. Reorientation in swimming direction, mediated by CheY3, is necessary for cells to escape from the porous biofilm matrix. We suggest that these components act sequentially: signaling launches dispersal by terminating matrix production and triggering matrix digestion, and subsequent cell motility permits escape from biofilms. This study lays the groundwork for interventions aimed at modulating V. cholerae biofilm dispersal to ameliorate disease.

Electrolocation? The evidence for redox-mediated taxis in Shewanella oneidensis

Shewanella oneidensis is a dissimilatory metal reducing bacterium and model for extracellular electron transfer (EET), a respiratory mechanism in which electrons are transferred out of the cell. In the last 10 years, migration to insoluble electron acceptors for EET has been shown to be nonrandom and tactic, seemingly in the absence of molecular or energy gradients that typically allow for taxis. As the ability to sense, locate, and respire electrodes has applications in bioelectrochemical technology, a better understanding of taxis in S. oneidensis is needed. While the EET conduits of S. oneidensis have been studied extensively, its taxis pathways and their interplay with EET are not yet understood, making investigation into taxis phenomena nontrivial. Since S. oneidensis is a member of an EET-encoding clade, the genetic circuitry of taxis to insoluble acceptors may be conserved. We performed a bioinformatic analysis of Shewanella genomes to identify S. oneidensis chemotaxis orthologs conserved in the genus. In addition to the previously reported core chemotaxis gene cluster, we identify several other conserved proteins in the taxis signaling pathway. We present the current evidence for the two proposed models of EET taxis, "electrokinesis" and flavin-mediated taxis, and highlight key areas in need of further investigation.

Folding heterogeneity in the essential human telomerase RNA three-way junction

Telomeres safeguard the genome by suppressing illicit DNA damage responses at chromosome termini. To compensate for incomplete DNA replication at telomeres, most continually dividing cells, including many cancers, express the telomerase ribonucleoprotein (RNP) complex. Telomerase maintains telomere length by catalyzing de novo synthesis of short DNA repeats using an internal telomerase RNA (TR) template. TRs from diverse species harbor structurally conserved domains that contribute to RNP biogenesis and function. In vertebrate TRs, the conserved regions 4 and 5 (CR4/5) fold into a three-way junction (TWJ) that binds directly to the telomerase catalytic protein subunit and is required for telomerase function. We have analyzed the structural properties of the human TR (hTR) CR4/5 domain using a combination of in vitro chemical mapping, secondary structural modeling, and single-molecule structural analysis. Our data suggest the essential P6.1 stem-loop within CR4/5 is not stably folded in the absence of the telomerase reverse transcriptase in vitro. Rather, the hTR CR4/5 domain adopts a heterogeneous ensemble of conformations. Finally, single-molecule FRET measurements of CR4/5 and a mutant designed to stabilize the P6.1 stem demonstrate that TERT binding selects for a structural conformation of CR4/5 that is not the dominant state of the TERT-free in vitro RNA ensemble.

Pathogenicity and virulence regulation of Vibrio cholerae at the interface of host-gut microbiome interactions

The Gram-negative bacterium Vibrio cholerae is responsible for the severe diarrheal pandemic disease cholera, representing a major global public health concern. This pathogen transitions from aquatic reservoirs into epidemics in human populations, and has evolved numerous mechanisms to sense this transition in order to appropriately regulate its gene expression for infection. At the intersection of pathogen and host in the gastrointestinal tract lies the community of native gut microbes, the gut microbiome. It is increasingly clear that the diversity of species and biochemical activities within the gut microbiome represents a driver of infection outcome, through their ability to manipulate the signals used by V. cholerae to regulate virulence and fitness in vivo. A better mechanistic understanding of how commensal microbial action interacts with V. cholerae pathogenesis may lead to novel prophylactic and therapeutic interventions for cholera. Here, we review a subset of this burgeoning field of research.

Quorum-sensing signaling by chironomid egg masses' microbiota, affects haemagglutinin/protease (HAP) production by Vibrio cholerae

Vibrio cholerae, the causative agent of cholera, is commonly isolated, along with other bacterial species, from chironomid insects (Diptera: Chironomidae). Nevertheless, its prevalence in the chironomid egg masses' microbiota is less than 0.5%. V. cholerae secretes haemagglutinin/protease (HAP) that degrades the gelatinous matrix of chironomid egg masses and prevents hatching. Quorum sensing (QS) activates HAP production in response to accumulation of bacterial autoinducers (AIs). Our aim was to define the impact of chironomid microbiota on HAP production by V. cholerae. To study QS signaling, we used V. cholerae bioluminescence reporter strains (QS-proficient O1 El-Tor wild-type and QS-deficient mutants) and different bacterial species that we isolated from chironomid egg masses. These egg mass isolates, as well as a synthetic AI-2, caused an enhancement in lux expression by a V. cholerae QS-deficient mutant. The addition of the egg mass bacterial isolate supernatant to the QS-deficient mutant also enhanced HAP production and egg mass degradation activities. Moreover, the V. cholerae wild-type strain was able to proliferate using egg masses as their sole carbon source, while the QS-deficient was not. The results demonstrate that members of the chironomid bacterial consortium produce external chemical cues that, like AI-2, induce expression of the hapA gene in V. cholerae. Understanding the interactions between V. cholerae and the insects' microbiota may help uncover the interactions between this pathogen and the human gut microbiota.

The chemosensory systems of Vibrio cholerae

Vibrio cholerae, the causative agent of the acute diarrheal disease cholera, is able to thrive in diverse habitats such as natural water bodies and inside human hosts. To ensure their survival, these bacteria rely on chemosensory pathways to sense and respond to changing environmental conditions. These pathways constitute a highly sophisticated cellular control system in Bacteria and Archaea. Reflecting the complex life cycle of V. cholerae, this organism has three different chemosensory pathways that together contain over 50 proteins expressed under different environmental conditions. Only one of them is known to control motility, while the function of the other two remains to be discovered. Here, we provide an overview of the chemosensory systems in V. cholerae and the advances toward understanding their structure and function.

A comprehensive review of therapeutic approaches available for the treatment of cholera

Objectives

The oral rehydration solution is the most efficient method to treat cholera; however, it does not interfere in the action mechanism of the main virulence factor produced by Vibrio cholerae, the cholera toxin (CT), and this disease still stands out as a problem for human health worldwide. This review aimed to describe therapeutic alternatives available in the literature, especially those related to the search for molecules acting upon the physiopathology of cholera.

Key findings

New molecules have offered a protection effect against diarrhoea induced by CT or even by infection from V. cholerae. The receptor regulator cystic fibrosis channel transmembrane (CFTR), monosialoganglioside (GM1), enkephalinase, AMP-activated protein kinase (AMPK), inhibitors of expression of virulence factors and activators of ADP-ribosylarginine hydrolase are the main therapeutic targets studied. Many of these molecules or extracts still present unclear action mechanisms.

Conclusions

Knowing therapeutic alternatives and their molecular mechanisms for the treatment of cholera could guide us to develop a new drug that could be used in combination with the rehydration solution.

Switching fatty acid metabolism by an RNA-controlled feed forward loop

Hfq (host factor for phage Q beta) is key for posttranscriptional gene regulation in many bacteria. Hfq's function is to stabilize sRNAs and to facilitate base-pairing with trans-encoded target mRNAs. Loss of Hfq typically results in pleiotropic phenotypes, and, in the major human pathogen Vibrio cholerae, Hfq inactivation has been linked to reduced virulence, failure to produce biofilms, and impaired intercellular communication. However, the RNA ligands of Hfq in V. cholerae are currently unknown. Here, we used RIP-seq (RNA immunoprecipitation followed by high-throughput sequencing) analysis to identify Hfq-bound RNAs in V. cholerae Our work revealed 603 coding and 85 noncoding transcripts associated with Hfq, including 44 sRNAs originating from the 3' end of mRNAs. Detailed investigation of one of these latter transcripts, named FarS (fatty acid regulated sRNA), showed that this sRNA is produced by RNase E-mediated maturation of the fabB 3'UTR, and, together with Hfq, inhibits the expression of two paralogous fadE mRNAs. The fabB and fadE genes are antagonistically regulated by the major fatty acid transcription factor, FadR, and we show that, together, FadR, FarS, and FadE constitute a mixed feed-forward loop regulating the transition between fatty acid biosynthesis and degradation in V. cholerae Our results provide the molecular basis for studies on Hfq in V. cholerae and highlight the importance of a previously unrecognized sRNA for fatty acid metabolism in this major human pathogen.

A model of strongly biased chemotaxis reveals the trade-offs of different bacterial migration strategies

Many bacteria actively bias their motility towards more favourable nutrient environments. In liquid, cells rotate their corkscrew-shaped flagella to swim, but in surface attached biofilms cells instead use grappling hook-like appendages called pili to pull themselves along. In both forms of motility, cells selectively alternate between relatively straight 'runs' and sharp reorientations to generate biased random walks up chemoattractant gradients. However, recent experiments suggest that swimming and biofilm cells employ fundamentally different strategies to generate chemotaxis: swimming cells typically suppress reorientations when moving up a chemoattractant gradient, whereas biofilm cells increase reorientations when moving down a chemoattractant gradient. The reason for this difference remains unknown. Here we develop a mathematical framework to understand how these different chemotactic strategies affect the distribution of cells at the population level. Current continuum models typically assume a weak bias in the reorientation rate and are not able to distinguish between these two strategies, so we derive a model for strong chemotaxis that resolves how both the drift and diffusive components depend on the underlying chemotactic strategy. We then test predictions from our continuum model against individual-based simulations and identify further refinements that allow our continuum model to resolve boundary effects. Our analyses reveal that the strategy employed by swimming cells yields a larger chemotactic drift, but the strategy used by biofilm cells allows them to more tightly aggregate where the chemoattractant is most abundant. This new modelling framework provides new quantitative insights into how the different chemical landscapes experienced by swimming and biofilm cells might select for divergent ways of generating chemotaxis.

Small RNA coaR contributes to intestinal colonization in Vibrio cholerae via the two-component system EnvZ/OmpR

Vibrio cholerae is a waterborne bacterium responsible for worldwide outbreaks of acute and fatal cholera. Recently, small regulatory RNAs (sRNAs) have become increasingly recognized as important regulators of virulence gene expression in response to environmental signals. In this study, we determined that two-component system EnvZ/OmpR was required for intestinal colonization in V. cholerae O1 EI Tor strain E12382. Analysis of the characteristics of OmpR revealed a potential binding site in the intergenic region between vc1470 and vc1471, and qRT-PCR showed that expression of the intergenic region increased 5.3-fold in the small intestine compared to LB medium. Race and northern blot assays were performed and demonstrated a new sRNA, coaR (cholerae osmolarity and acidity related regulatory RNA). A ΔcoaR mutant showed a deficient colonization ability in small intestine with CI of 0.15. We identified a target of coaR, tcpI, a negative regulator of the major pilin subunit of TcpA. The ΔtcpI mutant has an increased colonization with CI of 3.16. The expression of coaR increased 2.8-fold and 3.3-fold under relative acidic and hypertonic condition. In summary, coaR was induced under the condition of high osmolarity and acid stress via EnvZ/OmpR and explained that tcpI relieves pH-mediated repression of toxin co-regulated pilus synthesis.

Sugar-mediated regulation of a c-di-GMP phosphodiesterase in Vibrio cholerae

Biofilm formation protects bacteria from stresses including antibiotics and host immune responses. Carbon sources can modulate biofilm formation and host colonization in Vibrio cholerae, but the underlying mechanisms remain unclear. Here, we show that EIIA^Glc, a component of the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS), regulates the intracellular concentration of the cyclic dinucleotide c-di-GMP, and thus biofilm formation. The availability of preferred sugars such as glucose affects EIIA^Glc phosphorylation state, which in turn modulates the interaction of EIIA^Glc with a c-di-GMP phosphodiesterase (hereafter referred to as PdeS). In a Drosophila model of V. cholerae infection, sugars in the host diet regulate gut colonization in a manner dependent on the PdeS-EIIA^Glc interaction. Our results shed light into the mechanisms by which some nutrients regulate biofilm formation and host colonization.

Three autoinducer molecules act in concert to control virulence gene expression in Vibrio cholerae

Bacteria use quorum sensing to monitor cell density and coordinate group behaviours. In Vibrio cholerae, the causative agent of the diarrheal disease cholera, quorum sensing is connected to virulence gene expression via the two autoinducer molecules, AI-2 and CAI-1. Both autoinducers share one signal transduction pathway to control the production of AphA, a key transcriptional activator of biofilm formation and virulence genes. In this study, we demonstrate that the recently identified autoinducer, DPO, also controls AphA production in V. cholerae. DPO, functioning through the transcription factor VqmA and the VqmR small RNA, reduces AphA levels at the post-transcriptional level and consequently inhibits virulence gene expression. VqmR-mediated repression of AphA provides an important link between the AI-2/CAI-1 and DPO-dependent quorum sensing pathways in V. cholerae. Transcriptome analyses comparing the effect of single autoinducers versus autoinducer combinations show that quorum sensing controls the expression of ∼400 genes in V. cholerae and that all three autoinducers are required for a full quorum sensing response. Together, our data provide a global view on autoinducer interplay in V. cholerae and highlight the importance of RNA-based gene control for collective functions in this major human pathogen.

Regulated Proteolysis in Vibrio cholerae Allowing Rapid Adaptation to Stress Conditions

The lifecycle of the causative agent of the severe secretory diarrheal disease cholera, Vibrio cholerae, is characterized by the transition between two dissimilar habitats, i.e., as a natural inhabitant of aquatic ecosystems and as a pathogen in the human gastrointestinal tract. Vibrio cholerae faces diverse stressors along its lifecycle, which require effective adaptation mechanisms to facilitate the survival fitness. Not surprisingly, the pathogen's transcriptome undergoes global changes during the different stages of the lifecycle. Moreover, recent evidence indicates that several of the transcription factors (i.e., ToxR, TcpP, and ToxT) and alternative sigma factors (i.e., FliA, RpoS, and RpoE) involved in transcriptional regulations along the lifecycle are controlled by regulated proteolysis. This post-translational control ensures a fast strategy by the pathogen to control cellular checkpoints and thereby rapidly respond to changing conditions. In this review, we discuss selected targets for regulated proteolysis activated by various stressors, which represent a key feature for fast adaptation of V. cholerae.

Vibrio Flagellar Synthesis

Vibrio spp. are highly motile Gram-negative bacteria, ubiquitously found in aquatic environments. Some Vibrios are responsible for disease and morbidity of marine invertebrates and humans, while others are studied for their symbiotic interactions. Vibrio spp. are motile due to synthesis of flagella that rotate and propel the bacteria. Many Vibrio spp. synthesize monotrichous polar flagella (e.g., V. cholerae, V. alginolyticus); however, some synthesize peritrichous or lophotrichous flagella. Flagellar-mediated motility is intimately connected to biological and cellular processes such as chemotaxis, biofilm formation, colonization, and virulence of Vibrio spp. This review focuses on the polar flagellum and its regulation in regard to Vibrio virulence and environmental persistence.

Diversity of KIR, HLA Class I, and Their Interactions in Seven Populations of Sub-Saharan Africans

HLA class I and KIR sequences were determined for Dogon, Fulani, and Baka populations of western Africa, Mbuti of central Africa, and Datooga, Iraqw, and Hadza of eastern Africa. Study of 162 individuals identified 134 HLA class I alleles (41 HLA-A, 60 HLA-B, and 33 HLA-C). Common to all populations are three HLA-C alleles (C1⁺C*07:01, C1⁺C*07:02, and C2⁺C*06:02) but no HLA-A or -B Unexpectedly, no novel HLA class I was identified in these previously unstudied and anthropologically distinctive populations. In contrast, of 227 KIR detected, 22 are present in all seven populations and 28 are novel. A high diversity of HLA A-C-B haplotypes was observed. In six populations, most haplotypes are represented just once. But in the Hadza, a majority of haplotypes occur more than once, with 2 having high frequencies and 10 having intermediate frequencies. The centromeric (cen) part of the KIR locus exhibits an even balance between cenA and cenB in all seven populations. The telomeric (tel) part has an even balance of telA to telB in East Africa, but this changes across the continent to where telB is vestigial in West Africa. All four KIR ligands (A3/11, Bw4, C1, and C2) are present in six of the populations. HLA haplotypes of the Iraqw and Hadza encode two KIR ligands, whereas the other populations have an even balance between haplotypes encoding one and two KIR ligands. Individuals in these African populations have a mean of 6.8-8.4 different interactions between KIR and HLA class I, compared with 2.9-6.5 for non-Africans.

Worldwide genetic variation of the IGHV and TRBV immune receptor gene families in humans

This article presents a comprehensive study of the IGHV and TRBV gene families in a globally diverse sample of humans and shows that the two gene families exhibit starkly different patterns of variation.

The immunoglobulin heavy variable (IGHV) and T cell beta variable (TRBV) loci are among the most complex and variable regions in the human genome. Generated through a process of gene duplication/deletion and diversification, these loci can vary extensively between individuals in copy number and contain genes that are highly similar, making their analysis technically challenging. Here, we present a comprehensive study of the functional gene segments in the IGHV and TRBV loci, quantifying their copy number and single-nucleotide variation in a globally diverse sample of 109 (IGHV) and 286 (TRBV) humans from over a 100 populations. We find that the IGHV and TRBV gene families exhibit starkly different patterns of variation. In addition to providing insight into the different evolutionary paths of the IGHV and TRBV loci, our results are also important to the adaptive immune repertoire sequencing community, where the lack of frequencies of common alleles and copy number variants is hampering existing analytical pipelines.

Identification of in vivo Essential Genes of Vibrio vulnificus for Establishment of Wound Infection by Signature-Tagged Mutagenesis

Vibrio vulnificus can cause severe necrotic lesions within a short time. Recently, it has been reported that the numbers of wound infection cases in healthy hosts are increasing, for which surgical procedures are essential in many instances to eliminate the pathogen owing to its rapid proliferation. However, the mechanisms by which V. vulnificus can achieve wound infection in healthy hosts have not been elucidated. Here, we advance a systematic understanding of V. vulnificus wound infection through genome-wide identification of the relevant genes. Signature-tagged mutagenesis (STM) has been developed to identify functions required for the establishment of infection including colonization, rapid proliferation, and pathogenicity. Previously, STM had been regarded to be unsuitable for negative selection to detect the virulence genes of V. vulnificus owing to the low colonization and proliferation ability of this pathogen in the intestinal tract and systemic circulation. Alternatively, we successfully identified the virulence genes by applying STM to a murine model of wound infection. We examined a total of 5418 independent transposon insertion mutants by signature-tagged transposon mutagenesis and detected 71 clones as attenuated mutants consequent to disruption of genes by the insertion of a transposon. This is the first report demonstrating that the pathogenicity of V. vulnificus during wound infection is highly dependent on its characteristics: flagellar-based motility, siderophore-mediated iron acquisition system, capsular polysaccharide, lipopolysaccharide, and rapid chromosome partitioning. In particular, these functions during the wound infection process and are indispensable for proliferation in healthy hosts. Our results may thus allow the potential development of new strategies and reagents to control the proliferation of V. vulnificus and prevent human infections.

Short-term gain, long-term pain: the senescence life cycle and cancer

Originally thought of as a stress response end point, the view of cellular senescence has since evolved into one encompassing a wide range of physiological and pathological functions, including both protumorignic and antitumorigenic features. It has also become evident that senescence is a highly dynamic and heterogenous process. Efforts to reconcile the beneficial and detrimental features of senescence suggest that physiological functions require the transient presence of senescent cells in the tissue microenvironment. Here, we propose the concept of a physiological "senescence life cycle," which has pathological consequences if not executed in its entirety.

Cytotoxin- and Chemotaxis-Genes Cooperate to Promote Adhesion of Photobacterium damselae subsp. damselae

Photobacterium damselae subsp. damselae (Pdd) is an emerging pathogen of marine animals that sometimes causes serious infections in humans. Two related pore forming toxins, phobalysins P and C, and damselysin, a phospholipase D, confer strong virulence of Pdd in mice. Because infections by Pdd are typically caused following exposure of wounds to sea water we investigated how salinity impacts toxin activity, swimming, and association of Pdd with epithelial cells. These activities were low when bacteria were pre-cultured in media with 3.5% NaCl, the global average salinity of sea water. In contrast, lower salinity increased swimming of wild type Pdd peaking at 2% NaCl, hemolysis, and association with epithelial cells peaking at 1-1.5%. Previously, we have found that hemolysin genes enhance the association of Pdd with epithelial cells, but the underlying mechanisms have remained ill-defined. We here searched for potential links between hemolysin-production, chemotaxis and association of Pdd with target cells at varying salt concentrations. Unexpectedly, disruption of chemotaxis regulator cheA not only affected bacterial swimming and association with epithelial cells at intermediate to low salinity, but also reduced the production of plasmid-encoded phobalysin (PhlyP). The results thus reveal unforeseen links between chemotaxis regulators, a pore forming toxin and the association of a marine bacterium with target cells.

Quorum sensing controls Vibrio cholerae multicellular aggregate formation

Bacteria communicate and collectively regulate gene expression using a process called quorum sensing (QS). QS relies on group-wide responses to signal molecules called autoinducers. Here, we show that QS activates a new program of multicellularity in Vibrio cholerae. This program, which we term aggregation, is distinct from the canonical surface-biofilm formation program, which QS represses. Aggregation is induced by autoinducers, occurs rapidly in cell suspensions, and does not require cell division, features strikingly dissimilar from those characteristic of V. cholerae biofilm formation. Extracellular DNA limits aggregate size, but is not sufficient to drive aggregation. A mutagenesis screen identifies genes required for aggregate formation, revealing proteins involved in V. cholerae intestinal colonization, stress response, and a protein that distinguishes the current V. cholerae pandemic strain from earlier pandemic strains. We suggest that QS-controlled aggregate formation is important for V. cholerae to successfully transit between the marine niche and the human host.

Control of bacterial colonization in the glands and crypts

The epithelial cell layer of the major organs of the mammalian gastrointestinal (GI) tract is extensively invaginated into thousands of gland and crypt structures. These are lined by distinct sets of epithelial cells and may comprise discrete niches. The host maximizes the distance between the epithelial cell layer and GI-inhabiting microbes to limit inflammation, and these strategies also likely keep bacteria out of the glands and crypts. We discuss here the specific host processes that have been shown to restrict bacterial presence in the glands and crypts, specifically the immune system, acid, mucin, oxygen, and reactive oxygen species. Not surprisingly, microbes have evolved sophisticated strategies to overcome these host factors and reside close to the epithelium in the glands and crypts. Bacterial properties important for gland and crypt colonization include bacterial immunomodulatory molecules, chemotaxis, and the use of certain metabolites. Overall, these as-yet limited studies suggest there are specific host and bacterial properties that control gland and crypt colonization, contributing to the overall microbial spatial organization of the GI tract. However, there remains much to be discovered in this area.

The effect of bacterial chemotaxis on host infection and pathogenicity

Chemotaxis enables microorganisms to move according to chemical gradients. Although this process requires substantial cellular energy, it also affords key physiological benefits, including enhanced access to growth substrates. Another important implication of chemotaxis is that it also plays an important role in infection and disease, as chemotaxis signalling pathways are broadly distributed across a variety of pathogenic bacteria. Furthermore, current research indicates that chemotaxis is essential for the initial stages of infection in different human, animal and plant pathogens. This review focuses on recent findings that have identified specific bacterial chemoreceptors and corresponding chemoeffectors associated with pathogenicity. Pathogenicity-related chemoeffectors are either host and niche-specific signals or intermediates of the host general metabolism. Plant pathogens were found to contain an elevated number of chemotaxis signalling genes and functional studies demonstrate that these genes are critical for their ability to enter the host. The expanding body of knowledge of the mechanisms underlying chemotaxis in pathogens provides a foundation for the development of new therapeutic strategies capable of blocking infection and preventing disease by interfering with chemotactic signalling pathways.