CarRS Two-Component System Essential for Polymyxin B Resistance of Vibrio vulnificus Responds to Multiple Host Environmental Signals. - Related Documents




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67301.0000CarRS Two-Component System Essential for Polymyxin B Resistance of Vibrio vulnificus Responds to Multiple Host Environmental Signals. Enteropathogenic bacteria express two-component systems (TCSs) to sense and respond to host environments, developing resistance to host innate immune systems like cationic antimicrobial peptides (CAMPs). Although an opportunistic human pathogen Vibrio vulnificus shows intrinsic resistance to the CAMP-like polymyxin B (PMB), its TCSs responsible for resistance have barely been investigated. Here, a mutant exhibiting a reduced growth rate in the presence of PMB was screened from a random transposon mutant library of V. vulnificus, and response regulator CarR of the CarRS TCS was identified as essential for its PMB resistance. Transcriptome analysis revealed that CarR strongly activates the expression of the eptA, tolCV2, and carRS operons. In particular, the eptA operon plays a major role in developing the CarR-mediated PMB resistance. Phosphorylation of CarR by the sensor kinase CarS is required for the regulation of its downstream genes, leading to the PMB resistance. Nevertheless, CarR directly binds to specific sequences in the upstream regions of the eptA and carRS operons, regardless of its phosphorylation. Notably, the CarRS TCS alters its own activation state by responding to several environmental stresses, including PMB, divalent cations, bile salts, and pH change. Furthermore, CarR modulates the resistance of V. vulnificus to bile salts and acidic pH among the stresses, as well as PMB. Altogether, this study suggests that the CarRS TCS, in responding to multiple host environmental signals, could provide V. vulnificus with the benefit of surviving within the host by enhancing its optimal fitness during infection. IMPORTANCE Enteropathogenic bacteria have evolved multiple TCSs to recognize and appropriately respond to host environments. CAMP is one of the inherent host barriers that the pathogens encounter during the course of infection. In this study, the CarRS TCS of V. vulnificus was found to develop resistance to PMB, a CAMP-like antimicrobial peptide, by directly activating the expression of the eptA operon. Although CarR binds to the upstream regions of the eptA and carRS operons regardless of phosphorylation, phosphorylation of CarR is required for the regulation of the operons, resulting in the PMB resistance. Furthermore, the CarRS TCS determines the resistance of V. vulnificus to bile salts and acidic pH by differentially regulating its own activation state in response to these environmental stresses. Altogether, the CarRS TCS responds to multiple host-related signals, and thus could enhance the survival of V. vulnificus within the host, leading to successful infection.202337289068
69610.9993Identification of a two-component regulatory system involved in antimicrobial peptide resistance in Streptococcus pneumoniae. Two-component regulatory systems (TCS) are among the most widespread mechanisms that bacteria use to sense and respond to environmental changes. In the human pathogen Streptococcus pneumoniae, a total of 13 TCS have been identified and many of them have been linked to pathogenicity. Notably, TCS01 strongly contributes to pneumococcal virulence in several infection models. However, it remains one of the least studied TCS in pneumococci and its functional role is still unclear. In this study, we demonstrate that TCS01 cooperates with a BceAB-type ABC transporter to sense and induce resistance to structurally-unrelated antimicrobial peptides of bacterial origin that all target undecaprenyl-pyrophosphate or lipid II, which are essential precursors of cell wall biosynthesis. Even though tcs01 and bceAB genes do not locate in the same gene cluster, disruption of either of them equally sensitized the bacterium to the same set of antimicrobial peptides. We show that the key function of TCS01 is to upregulate the expression of the transporter, while the latter appears the main actor in resistance. Electrophoretic mobility shift assays further demonstrated that the response regulator of TCS01 binds to the promoter region of the bceAB genes, implying a direct control of these genes. The BceAB transporter was overexpressed and purified from E. coli. After reconstitution in liposomes, it displayed substantial ATPase and GTPase activities that were stimulated by antimicrobial peptides to which it confers resistance to, revealing new functional features of a BceAB-type transporter. Altogether, this inducible defense mechanism likely contributes to the survival of the opportunistic microorganism in the human host, in which competition among commensal microorganisms is a key determinant for effective host colonization and invasive path.202235395062
830820.9993PhoPQ Regulates Quinolone and Cephalosporin Resistance Formation in Salmonella Enteritidis at the Transcriptional Level. The two-component system (TCS) PhoPQ has been demonstrated to be crucial for the formation of resistance to quinolones and cephalosporins in Salmonella Enteritidis (S. Enteritidis). However, the mechanism underlying PhoPQ-mediated antibiotic resistance formation remains poorly understood. Here, it was shown that PhoP transcriptionally regulated an assortment of genes associated with envelope homeostasis, the osmotic stress response, and the redox balance to confer resistance to quinolones and cephalosporins in S. Enteritidis. Specifically, cells lacking the PhoP regulator, under nalidixic acid and ceftazidime stress, bore a severely compromised membrane on the aspects of integrity, fluidity, and permeability, with deficiency to withstand osmolarity stress, an increased accumulation of intracellular reactive oxygen species, and dysregulated redox homeostasis, which are unfavorable for bacterial survival. The phosphorylated PhoP elicited transcriptional alterations of resistance-associated genes, including the outer membrane porin ompF and the aconitate hydratase acnA, by directly binding to their promoters, leading to a limited influx of antibiotics and a well-maintained intracellular metabolism. Importantly, it was demonstrated that the cavity of the PhoQ sensor domain bound to and sensed quinolones/cephalosporins via the crucial surrounding residues, as their mutations abrogated the binding and PhoQ autophosphorylation. This recognition mode promoted signal transduction that activated PhoP, thereby modulating the transcription of downstream genes to accommodate cells to antibiotic stress. These findings have revealed how bacteria employ a specific TCS to sense antibiotics and combat them, suggesting PhoPQ as a potential drug target with which to surmount S. Enteritidis. IMPORTANCE The prevalence of quinolone and cephalosporin-resistant S. Enteritidis is of increasing clinical concern. Thus, it is imperative to identify novel therapeutic targets with which to treat S. Enteritidis-associated infections. The PhoPQ two-component system is conserved across a variety of Gram-negative pathogens, by which bacteria adapt to a range of environmental stimuli. Our earlier work has demonstrated the importance of PhoPQ in the resistance formation in S. Enteritidis to quinolones and cephalosporins. In the current work, we identified a global profile of genes that are regulated by PhoP under antibiotic stresses, with a focus on how PhoP regulated downstream genes, either positively or negatively. Additionally, we established that PhoQ sensed quinolones and cephalosporins in a manner of directly binding to them. These identified genes and pathways that are mediated by PhoPQ represent promising targets for the development of a drug potentiator with which to neutralize antibiotic resistance in S. Enteritidis.202337184399
70530.9993First structure of the polymyxin resistance proteins. PmrA/PmrB and PhoP/PhoQ are a pair of two-component systems (TCSs) that allow the Gram-negative bacteria to survive the cationic antimicrobial peptide polymyxin B. The two TCSs are linked by the polymyxin resistance protein, PmrD. The PhoP-activated PmrD protects the phosphorylated response regulator PmrA from dephosphorylation, and promotes the transcription of PmrA-activated genes responsible for polymyxin resistance. PmrD is the first protein identified to mediate the connectivity between two TCSs by protecting the phosphorylated response regulator of the downstream TCS. PmrD shows no homology to proteins with known structures. We present here the solution structure of PmrD from Escherichia coli, the first three-dimensional structure of the PmrD family. Our study provides the structural basis of the novel interacting mechanism of bacterial two-component signal-transduction systems.200717686460
831040.9993Dynamic heterogeneity in an E. coli stress response regulon mediates gene activation and antimicrobial peptide tolerance. The bacterial stress response is an intricately regulated system that plays a critical role in cellular resistance to drug treatment. The complexity of this response is further complicated by cell-to-cell heterogeneity in the expression of bacterial stress response genes. These genes are often organized into networks comprising one or more transcriptional regulators that control expression of a suite of downstream genes. While the expression heterogeneity of many of these upstream regulators has been characterized, the way in which this variability affects the larger downstream stress response remains hard to predict, prompting two key questions. First, how does heterogeneity and expression noise in stress response regulators propagate to the diverse downstream genes in their regulons. Second, when expression levels vary, how do multiple downstream genes act together to protect cells from stress. To address these questions, we focus on the transcription factor PhoP, a critical virulence regulator which coordinates pathogenicity in several gram-negative species. We use optogenetic stimulation to precisely control PhoP expression levels and examine how variations in PhoP affect the downstream activation of genes in the PhoP regulon. We find that these downstream genes exhibit differences both in mean expression level and sensitivity to increasing levels of PhoP. These response functions can also vary between individual cells, increasing heterogeneity in the population. We tie these variations to cell survival when bacteria are exposed to a clinically-relevant antimicrobial peptide, showing that high expression of the PhoP-regulon gene pmrD provides a protective effect against Polymyxin B. Overall, we demonstrate that even subtle heterogeneity in expression of a stress response regulator can have clear consequences for enabling bacteria to survive stress.202439677761
69850.9992Genome-wide transcriptional changes induced by phagocytosis or growth on bacteria in Dictyostelium. BACKGROUND: Phagocytosis plays a major role in the defense of higher organisms against microbial infection and provides also the basis for antigen processing in the immune response. Cells of the model organism Dictyostelium are professional phagocytes that exploit phagocytosis of bacteria as the preferred way to ingest food, besides killing pathogens. We have investigated Dictyostelium differential gene expression during phagocytosis of non-pathogenic bacteria, using DNA microarrays, in order to identify molecular functions and novel genes involved in phagocytosis. RESULTS: The gene expression profiles of cells incubated for a brief time with bacteria were compared with cells either incubated in axenic medium or growing on bacteria. Transcriptional changes during exponential growth in axenic medium or on bacteria were also compared. We recognized 443 and 59 genes that are differentially regulated by phagocytosis or by the different growth conditions (growth on bacteria vs. axenic medium), respectively, and 102 genes regulated by both processes. Roughly one third of the genes are up-regulated compared to macropinocytosis and axenic growth. Functional annotation of differentially regulated genes with different tools revealed that phagocytosis induces profound changes in carbohydrate, amino acid and lipid metabolism, and in cytoskeletal components. Genes regulating translation and mitochondrial biogenesis are mostly up-regulated. Genes involved in sterol biosynthesis are selectively up-regulated, suggesting a shift in membrane lipid composition linked to phagocytosis. Very few changes were detected in genes required for vesicle fission/fusion, indicating that the intracellular traffic machinery is mostly in common between phagocytosis and macropinocytosis. A few putative receptors, including GPCR family 3 proteins, scaffolding and adhesion proteins, components of signal transduction and transcription factors have been identified, which could be part of a signalling complex regulating phagocytosis and adaptational downstream responses. CONCLUSION: The results highlight differences between phagocytosis and macropinocytosis, and provide the basis for targeted functional analysis of new candidate genes and for comparison studies with transcriptomes during infection with pathogenic bacteria.200818559084
69760.9992Step-wise loss of bacterial flagellar torsion confers progressive phagocytic evasion. Phagocytosis of bacteria by innate immune cells is a primary method of bacterial clearance during infection. However, the mechanisms by which the host cell recognizes bacteria and consequentially initiates phagocytosis are largely unclear. Previous studies of the bacterium Pseudomonas aeruginosa have indicated that bacterial flagella and flagellar motility play an important role in colonization of the host and, importantly, that loss of flagellar motility enables phagocytic evasion. Here we use molecular, cellular, and genetic methods to provide the first formal evidence that phagocytic cells recognize bacterial motility rather than flagella and initiate phagocytosis in response to this motility. We demonstrate that deletion of genes coding for the flagellar stator complex, which results in non-swimming bacteria that retain an initial flagellar structure, confers resistance to phagocytic binding and ingestion in several species of the gamma proteobacterial group of Gram-negative bacteria, indicative of a shared strategy for phagocytic evasion. Furthermore, we show for the first time that susceptibility to phagocytosis in swimming bacteria is proportional to mot gene function and, consequently, flagellar rotation since complementary genetically- and biochemically-modulated incremental decreases in flagellar motility result in corresponding and proportional phagocytic evasion. These findings identify that phagocytic cells respond to flagellar movement, which represents a novel mechanism for non-opsonized phagocytic recognition of pathogenic bacteria.201121949654
66570.9992Functional versatility of Zur in metal homeostasis, motility, biofilm formation, and stress resistance in Yersinia pseudotuberculosis. Zur (zinc uptake regulator) is a significant member of the Fur (ferric uptake regulator) superfamily, which is widely distributed in bacteria. Zur plays crucial roles in zinc homeostasis and influences cell development and environmental adaptation in various species. Yersinia pseudotuberculosis is a Gram-negative enteric that pathogen usually serves as a model organism in pathogenicity studies. The regulatory effects of Zur on the zinc transporter ZnuABC and the protein secretion system T6SS have been documented in Y. pseudotuberculosis. In this study, a comparative transcriptomics analysis between a ∆zur mutant and the wild-type (WT) strain of Y. pseudotuberculosis was conducted using RNA-seq. This analysis revealed global regulation by Zur across multiple functional categories, including membrane transport, cell motility, and molecular and energy metabolism. Additionally, Zur mediates the homeostasis not only of zinc but also ferric and magnesium in vivo. There was a notable decrease in 35 flagellar biosynthesis and assembly-related genes, leading to reduced swimming motility in the ∆zur mutant strain. Furthermore, Zur upregulated multiple simple sugar and oligopeptide transport system genes by directly binding to their promoters. The absence of Zur inhibited biofilm formation as well as reduced resistance to chloramphenicol and acidic stress. This study illustrates the comprehensive regulatory functions of Zur, emphasizing its importance in stress resistance and pathogenicity in Y. pseudotuberculosis. IMPORTANCE: Bacteria encounter diverse stresses in the environment and possess essential regulators to modulate the expression of genes in responding to the stresses for better fitness and survival. Zur (zinc uptake regulator) plays a vital role in zinc homeostasis. Studies of Zur from multiple species reviewed that it influences cell development, stress resistance, and virulence of bacteria. Y. pseudotuberculosis is an enteric pathogen that serves a model organism in the study of pathogenicity, virulence factors, and mechanism of environmental adaptation. In this study, transcriptomics analysis of Zur's regulons was conducted in Y. pseudotuberculosis. The functions of Zur as a global regulator in metal homeostasis, motility, nutrient acquisition, glycan metabolism, and nucleotide metabolism, in turn, increasing the biofilm formation, stress resistance, and virulence were reviewed. The importance of Zur in environmental adaptation and pathogenicity of Y. pseudotuberculosis was emphasized.202438534119
71380.9992OxyR-activated expression of Dps is important for Vibrio cholerae oxidative stress resistance and pathogenesis. Vibrio cholerae is the causative agent of cholera, a dehydrating diarrheal disease. This Gram-negative pathogen is able to modulate its gene expression in order to combat stresses encountered in both aquatic and host environments, including stress posed by reactive oxygen species (ROS). In order to further the understanding of V. cholerae's transcriptional response to ROS, we performed an RNA sequencing analysis to determine the transcriptional profile of V. cholerae when exposed to hydrogen hydroperoxide. Of 135 differentially expressed genes, VC0139 was amongst the genes with the largest induction. VC0139 encodes a protein homologous to the DPS (DNA-binding protein from starved cells) protein family, which are widely conserved and are implicated in ROS resistance in other bacteria. Using a promoter reporter assay, we show that during exponential growth, dps is induced by H2O2 in a manner dependent on the ROS-sensing transcriptional regulator, OxyR. Upon entry into stationary phase, the major stationary phase regulator RpoS is required to transcribe dps. Deletion of dps impaired V. cholerae resistance to both inorganic and organic hydroperoxides. Furthermore, we show that Dps is involved in resistance to multiple environmental stresses. Finally, we found that Dps is important for V. cholerae adult mouse colonization, but becomes dispensable in the presence of antioxidants. Taken together, our results suggest that Dps plays vital roles in both V. cholerae stress resistance and pathogenesis.201728151956
68790.9992RpoS-Regulated Genes and Phenotypes in the Phytopathogenic Bacterium Pectobacterium atrosepticum. The alternative sigma factor RpoS is considered to be one of the major regulators providing stress resistance and cross-protection in bacteria. In phytopathogenic bacteria, the effects of RpoS have not been analyzed with regard to cross-protection, and genes whose expression is directly or indirectly controlled by RpoS have not been determined at the whole-transcriptome level. Our study aimed to determine RpoS-regulated genes and phenotypes in the phytopathogenic bacterium Pectobacterium atrosepticum. Knockout of the rpoS gene in P. atrosepticum affected the long-term starvation response, cross-protection, and virulence toward plants with enhanced immune status. The whole-transcriptome profiles of the wild-type P. atrosepticum strain and its ΔrpoS mutant were compared under different experimental conditions, and functional gene groups whose expression was affected by RpoS were determined. The RpoS promoter motif was inferred within the promoter regions of the genes affected by rpoS deletion, and the P. atrosepticum RpoS regulon was predicted. Based on RpoS-controlled phenotypes, transcriptome profiles, and RpoS regulon composition, the regulatory role of RpoS in P. atrosepticum is discussed.202338139177
8311100.9992Perturbation of Quorum Sensing after the Acquisition of Bacteriophage Resistance Could Contribute to Novel Traits in Vibrio alginolyticus. Bacteria employ a wide range of molecular mechanisms to confer resistance to bacteriophages, and these mechanisms are continuously being discovered and characterized. However, there are instances where certain bacterial species, despite lacking these known mechanisms, can still develop bacteriophage resistance through intricate metabolic adaptation strategies, potentially involving mutations in transcriptional regulators or phage receptors. Vibrio species have been particularly useful for studying the orchestrated metabolic responses of Gram-negative marine bacteria in various challenges. In a previous study, we demonstrated that Vibrio alginolyticus downregulates the expression of specific receptors and transporters in its membrane, which may enable the bacterium to evade infection by lytic bacteriophages. In our current study, our objective was to explore how the development of bacteriophage resistance in Vibrio species disrupts the quorum-sensing cascade, subsequently affecting bacterial physiology and metabolic capacity. Using a real-time quantitative PCR (rt-QPCR) platform, we examined the expression pattern of quorum-sensing genes, auto-inducer biosynthesis genes, and cell density regulatory proteins in phage-resistant strains. Our results revealed that bacteriophage-resistant bacteria downregulate the expression of quorum-sensing regulatory proteins, such as LuxM, LuxN, and LuxP. This downregulation attenuates the normal perception of quorum-sensing peptides and subsequently diminishes the expression of cell density regulatory proteins, including LuxU, aphA, and LuxR. These findings align with the diverse phenotypic traits observed in the phage-resistant strains, such as altered biofilm formation, reduced planktonic growth, and reduced virulence. Moreover, the transcriptional depletion of aphA, the master regulator associated with low cell density, was linked to the downregulation of genes related to virulence. This phenomenon appears to be phage-specific, suggesting a finely tuned metabolic adaptation driven by phage-host interaction. These findings contribute to our understanding of the role of Vibrio species in microbial marine ecology and highlight the complex interplay between phage resistance, quorum sensing, and bacterial physiology.202337764117
761110.9992Copper-responsive gene regulation in bacteria. Copper is an essential cofactor of various enzymes, but free copper is highly toxic to living cells. To maintain cellular metabolism at different ambient copper concentrations, bacteria have evolved specific copper homeostasis systems that mostly act as defence mechanisms. As well as under free-living conditions, copper defence is critical for virulence in pathogenic bacteria. Most bacteria synthesize P-type copper export ATPases as principal defence determinants when copper concentrations exceed favourable levels. In addition, many bacteria utilize resistance-nodulation-cell division (RND)-type efflux systems and multicopper oxidases to cope with excess copper. This review summarizes our current knowledge on copper-sensing transcriptional regulators, which we assign to nine different classes. Widespread one-component regulators are CueR, CopY and CsoR, which were initially identified in Escherichia coli, Enterococcus hirae and Mycobacterium tuberculosis, respectively. CueR activates homeostasis gene expression at elevated copper concentrations, while CopY and CsoR repress their target genes under copper-limiting conditions. Besides these one-component systems, which sense the cytoplasmic copper status, many Gram-negative bacteria utilize two-component systems, which sense periplasmic copper concentrations. In addition to these well-studied transcriptional factors, copper control mechanisms acting at the post-transcriptional and the post-translational levels will be discussed.201222918892
706120.9992Effect of PhoP-PhoQ activation by broad repertoire of antimicrobial peptides on bacterial resistance. Pathogenic bacteria can resist their microenvironment by changing the expression of virulence genes. In Salmonella typhimurium, some of these genes are controlled by the two-component system PhoP-PhoQ. Studies have shown that activation of the system by cationic antimicrobial peptides (AMPs) results, among other changes, in outer membrane remodeling. However, it is not fully clear what characteristics of AMPs are required to activate the PhoP-PhoQ system and whether activation can induce resistance to the various AMPs. For that purpose, we investigated the ability of a broad repertoire of AMPs to traverse the inner membrane, to activate the PhoP-PhoQ system, and to induce bacterial resistance. The AMPs differ in length, composition, and net positive charge, and the tested bacteria include two wild-type (WT) Salmonella strains and their corresponding PhoP-PhoQ knock-out mutants. A lacZ-reporting system was adapted to follow PhoP-PhoQ activation. The data revealed that: (i) a good correlation exists among the extent of the positive charge, hydrophobicity, and amphipathicity of an AMP and its potency to activate PhoP-PhoQ; (ii) a +1 charged peptide containing histidines was highly potent, suggesting the existence of an additional mechanism independent of the peptide charge; (iii) the WT bacteria are more resistant to AMPs that are potent activators of PhoP-PhoQ; (iv) only a subset of AMPs, independent of their potency to activate the system, is more toxic to the mutated bacteria compared with the WT strains; and (v) short term exposure of WT bacteria to these AMPs does not enhance resistance. Overall, this study advances our understanding of the molecular mechanism by which AMPs activate PhoP-PhoQ and induce bacterial resistance. It also reveals that some AMPs can overcome such a resistance mechanism.201222158870
727130.9992Bacillus subtilis extracytoplasmic function (ECF) sigma factors and defense of the cell envelope. Bacillus subtilis provides a model for investigation of the bacterial cell envelope, the first line of defense against environmental threats. Extracytoplasmic function (ECF) sigma factors activate genes that confer resistance to agents that threaten the integrity of the envelope. Although their individual regulons overlap, σ(W) is most closely associated with membrane-active agents, σ(X) with cationic antimicrobial peptide resistance, and σ(V) with resistance to lysozyme. Here, I highlight the role of the σ(M) regulon, which is strongly induced by conditions that impair peptidoglycan synthesis and includes the core pathways of envelope synthesis and cell division, as well as stress-inducible alternative enzymes. Studies of these cell envelope stress responses provide insights into how bacteria acclimate to the presence of antibiotics.201626901131
730140.9992How intracellular bacteria survive: surface modifications that promote resistance to host innate immune responses. Bacterial pathogens regulate the expression of virulence factors in response to environmental signals. In the case of salmonellae, many virulence factors are regulated via PhoP/PhoQ, a two-component signal transduction system that is repressed by magnesium and calcium in vitro. PhoP/PhoQ-activated genes promote intracellular survival within macrophages, whereas PhoP-repressed genes promote entrance into epithelial cells and macrophages by macropinocytosis and stimulate epithelial cell cytokine production. PhoP-activated genes include those that alter the cell envelope through structural alterations of lipopolysaccharide and lipid A, the bioactive component of lipopolysaccharide. PhoP-activated changes in the bacterial envelope likely promote intracellular survival by increasing resistance to host cationic antimicrobial peptides and decreasing host cell cytokine production.199910081503
8298150.9992Cellular Management of Zinc in Group B Streptococcus Supports Bacterial Resistance against Metal Intoxication and Promotes Disseminated Infection. Zinc is an essential trace element for normal bacterial physiology but, divergently, can intoxicate bacteria at high concentrations. Here, we define the molecular systems for Zn detoxification in Streptococcus agalactiae, also known as group B streptococcus, and examine the effects of resistance to Zn stress on virulence. We compared the growth of wild-type bacteria and mutants deleted for the Zn exporter, czcD, and the response regulator, sczA, using Zn-stress conditions in vitro Macrophage antibiotic protection assays and a mouse model of disseminated infection were used to assess virulence. Global bacterial transcriptional responses to Zn stress were defined by RNA sequencing and quantitative reverse transcription-PCR. czcD and sczA enabled S. agalactiae to survive Zn stress, with the putative CzcD efflux system activated by SczA. Additional genes activated in response to Zn stress encompassed divalent cation transporters that contribute to regulation of Mn and Fe homeostasis. In vivo, the czcD-sczA Zn management axis supported virulence in the blood, heart, liver, and bladder. Additionally, several genes not previously linked to Zn stress in any bacterium, including, most notably, arcA for arginine deamination, also mediated resistance to Zn stress, representing a novel molecular mechanism of bacterial resistance to metal intoxication. Taken together, these findings show that S. agalactiae responds to Zn stress by sczA regulation of czcD, with additional novel mechanisms of resistance supported by arcA, encoding arginine deaminase. Cellular management of Zn stress in S. agalactiae supports virulence by facilitating bacterial survival in the host during systemic infection.IMPORTANCEStreptococcus agalactiae, also known as group B streptococcus, is an opportunistic pathogen that causes various diseases in humans and animals. This bacterium has genetic systems that enable zinc detoxification in environments of metal stress, but these systems remain largely undefined. Using a combination of genomic, genetic, and cellular assays, we show that this pathogen controls Zn export through CzcD to manage Zn stress and utilizes a system of arginine deamination never previously linked to metal stress responses in bacteria to survive metal intoxication. We show that these systems are crucial for survival of S. agalactiaein vitro during Zn stress and also enhance virulence during systemic infection in mice. These discoveries establish new molecular mechanisms of resistance to metal intoxication in bacteria; we suggest these mechanisms operate in other bacteria as a way to sustain microbial survival under conditions of metal stress, including in host environments.202134011683
668160.9992c-di-GMP regulates the resistance of Pseudomonas aeruginosa to heat shock and aminoglycoside antibiotics by targeting the σ factor RpoH. Cyclic di-GMP (c-di-GMP) is a second messenger molecule that is widely distributed in bacteria and plays various physiologically important regulatory roles through interactions with a variety of effector molecules. Sigma (σ) factors are the predominant transcription factors involved in transcription regulation in bacteria. While c-di-GMP has been shown to bind to a range of transcription factors, c-di-GMP-binding σ factors have never been reported before. In a c-di-GMP/σ factors binding screen, we identified the σ factor RpoH as a c-di-GMP-responsive transcription factor in Pseudomonas aeruginosa PAO1. We further show that the binding of c-di-GMP to RpoH inhibits binding of RpoH to the promoters of its target genes such as asrA and dnaK, thereby downregulating the expression of these genes and reducing the resistance of P. aeruginosa to heat shock and aminoglycoside antibiotics. RpoH from Escherichia coli, Burkholderia thailandensis and Agrobacterium tumefaciens are also capable of binding c-di-GMP, suggesting that c-di-GMP-mediated control of the activity of RpoH is conserved in members of Proteobacteria.202641005124
686170.9992SigB-dependent general stress response in Bacillus subtilis and related gram-positive bacteria. One of the strongest and most noticeable responses of Bacillus subtilis cells to a range of stress and starvation stimuli is the dramatic induction of about 150 SigB-dependent general stress genes. The activity of SigB itself is tightly regulated by a complex signal transduction cascade with at least three main signaling pathways that respond to environmental stress, energy depletion, or low temperature. The SigB-dependent response is conserved in related gram-positive bacteria but is missing in strictly anaerobic or in some facultatively anaerobic gram-positive bacteria. It covers functions from nonspecific and multiple stress resistance to the control of virulence in pathogenic bacteria. A comprehensive understanding of this crucial stress response is essential not only for bacterial physiology but also for applied microbiology, including pathogenicity and pathogen control.200718035607
731180.9991Regulation of lipid A modifications by Salmonella typhimurium virulence genes phoP-phoQ. Bacterial pathogenesis requires proteins that sense host microenvironments and respond by regulating virulence gene transcription. For Salmonellae, one such regulatory system is PhoP-PhoQ, which regulates genes required for intracellular survival and resistance to cationic peptides. Analysis by mass spectrometry revealed that Salmonella typhimurium PhoP-PhoQ regulated structural modifications of lipid A, the host signaling portion of lipopolysaccharide (LPS), by the addition of aminoarabinose and 2-hydroxymyristate. Structurally modified lipid A altered LPS-mediated expression of the adhesion molecule E-selectin by endothelial cells and tumor necrosis factor-alpha expression by adherent monocytes. Thus, altered responses to environmentally induced lipid A structural modifications may represent a mechanism for bacteria to gain advantage within host tissues.19979092473
8300190.9991The Copper Resistome of Group B Streptococcus Reveals Insight into the Genetic Basis of Cellular Survival during Metal Ion Stress. In bacteria, copper (Cu) can support metabolic processes as an enzymatic cofactor but can also cause cell damage if present in excess, leading to intoxication. In group B Streptococcus (GBS), a system for control of Cu efflux based on the prototypical cop operon supports survival during Cu stress. In some other bacteria, genetic systems additional to the cop operon are engaged during Cu stress and also contribute to the management of cellular Cu homeostasis. Here, we examined genetic systems beyond the cop operon in GBS for regions that contribute to survival of GBS in Cu stress using a forward genetic screen and probe of the entire bacterial genome. A high-density mutant library, generated using pGh9-ISS1, was used to expose GBS to Cu stress and compare it to nonexposed controls en masse. Eight genes were identified as essential for GBS survival in Cu stress, whereas five genes constrained GBS growth in Cu stress. The genes encode varied factors including enzymes for metabolism, cell wall synthesis, transporters, and cell signaling factors. Targeted mutation of the genes validated their roles in GBS resistance to Cu stress. Excepting copA, the genes identified are new to the area of bacterial metal ion intoxication. We conclude that a discrete and limited suite of genes beyond the cop operon in GBS contributes to a repertoire of mechanisms used to survive Cu stress in vitro and achieve cellular homeostasis. IMPORTANCE Genetic systems for copper (Cu) homeostasis in bacteria, including streptococci, are vital to survive metal ion stress. Genetic systems that underpin survival of GBS during Cu stress, beyond the archetypal cop operon for Cu management, are undefined. We show that Streptococcus resists Cu intoxication by utilizing a discrete and limited suite of genes beyond the cop operon, including several genes that are new to the area of bacterial cell metal ion homeostasis. The Cu resistome of GBS defined here enhances our understanding of metal ion homeostasis in GBS.202235404113