C-terminal Poly-histidine Tags Alter Escherichia coli Polyphosphate Kinase Activity and Susceptibility to Inhibition

In Escherichia coli, many environmental stressors trigger polyphosphate (polyP) synthesis by polyphosphate kinase (PPK1), including heat, nutrient restriction, toxic compounds, and osmotic imbalances. PPK1 is essential for virulence in many pathogens and has been the target of multiple screens for small molecule inhibitors that might serve as new anti-virulence drugs. However, the mechanisms by which PPK1 activity and polyP synthesis are regulated are poorly understood. Our previous attempts to uncover PPK1 regulatory elements resulted in the discovery of PPK1* mutants, which accumulate more polyP in vivo, but do not produce more in vitro. In attempting to further characterize these mutant enzymes, we discovered that the most commonly-used PPK1 purification method - Ni-affinity chromatography using a C-terminal poly-histidine tag - altered intrinsic aspects of the PPK1 enzyme, including specific activity, oligomeric state, and kinetic values. We developed an alternative purification strategy using a C-terminal C-tag which did not have these effects. Using this strategy, we were able to demonstrate major differences in the in vitro response of PPK1 to 5-aminosalicylic acid, a known PPK1 inhibitor, and observed several key differences between the wild-type and PPK1* enzymes, including changes in oligomeric distribution, increased enzymatic activity, and increased resistance to both product (ADP) and substrate (ATP) inhibition, that help to explain their in vivo effects. Importantly, our results indicate that the C-terminal poly-histidine tag is inappropriate for purification of PPK1, and that any in vitro studies or inhibitor screens performed with such tags need to be reconsidered in that light.

Inorganic Polyphosphate in Host and Microbe Biology

Inorganic polyphosphate (polyP) is produced by both bacteria and their eukaryotic hosts, and it appears to play multiple important roles in the interactions between those organisms. However, the detailed mechanisms of how polyP synthesis is regulated in bacteria, and how it influences both bacterial and host biology, remain largely unexplored. In this review, we examine recent developments in the understanding of how bacteria regulate the synthesis of polyP, what roles polyP plays in controlling virulence in pathogenic bacteria, and the effects of polyP on the mammalian immune system, as well as progress on developing drugs that may be able to target bacterial polyP synthesis as novel means of treating infectious disease.

A quantum dot fluorescent microsphere based immunochromatographic strip for detection of brucellosis

BACKGROUND

Brucellosis is a serious zoonosis disease that frequently causes significant economic loss in animal husbandry and threatens human health. Therefore, we established a rapid, accurate, simple and sensitive fluorescent immunochromatographic strip test (ICST) based on quantum dots (QDs) for detection the antibodies of Brucella infection animals serum.

RESULTS

The test strips were successfully prepared by quantum dot fluorescent microspheres (QDFM) as tracers, which were covalently coupled to an outer membrane protein of Brucella OMP22. The outer membrane protein OMP28 and monoclonal antibodies of OMP22 were separately dispensed onto a nitrocellulose membrane as test and quality control lines, respectively. The critical threshold for determining negative or positive through the ratio of the fluorescent signal of the test line and the control line (H_T / H_C) is 0.0492. The repeatability was excellent with an overall average CV of 8.78%. Under optimum conditions, the limit of detection was 1.05 ng/mL (1:512 dilution). With regard to the detection of brucellosis in 150 clinical samples, the total coincidence rate of ICST and Rose Bengal plate test (RBPT) was 97.3%, the coincidence rate of positive samples was 98.8%, the coincidence rate of negative samples was 95.3%, the sensitivity of RBPT is 1:32, and no cross reaction with the sera of other related diseases was observed.

CONCLUSION

In our present study, the QDFM has promising application for on-site screening of brucellosis owing to its high detection speed, high sensitivity, high specificity and low cost.

The Role of Neutrophils in Brucellosis

Brucellosis is a bacterial disease of domestic animals and humans. The pathogenic ability of Brucella organisms relies on their stealthy strategy and their capacity to replicate within host cells and to induce long-lasting infections. Brucella organisms barely induce neutrophil activation and survive within these leukocytes by resisting microbicidal mechanisms. Very few Brucella-infected neutrophils are found in the target organs, except for the bone marrow, early in infection. Still, Brucella induces a mild reactive oxygen species formation and, through its lipopolysaccharide, promotes the premature death of neutrophils, which release chemokines and express "eat me" signals. This effect drives the phagocytosis of infected neutrophils by mononuclear cells that become thoroughly susceptible to Brucella replication and vehicles for bacterial dispersion. The premature death of the infected neutrophils proceeds without NETosis, necrosis/oncosis, or classical apoptosis morphology. In the absence of neutrophils, the Th1 response exacerbates and promotes bacterial removal, indicating that Brucella-infected neutrophils dampen adaptive immunity. This modulatory effect opens a window for bacterial dispersion in host tissues before adaptive immunity becomes fully activated. However, the hyperactivation of immunity is not without a price, since neutropenic Brucella-infected animals develop cachexia in the early phases of the disease. The delay in the immunological response seems a sine qua non requirement for the development of long-lasting brucellosis. This property may be shared with other pathogenic alphaproteobacteria closely related to Brucella We propose a model in which Brucella-infected polymorphonuclear neutrophils (PMNs) function as "Trojan horse" vehicles for bacterial dispersal and as modulators of the Th1 adaptive immunity in infection.

Interactions between DksA and Stress-Responsive Alternative Sigma Factors Control Inorganic Polyphosphate Accumulation in Escherichia coli

Bacteria synthesize inorganic polyphosphate (polyP) in response to a variety of different stress conditions. polyP protects bacteria by acting as a protein-stabilizing chaperone, metal chelator, or regulator of protein function, among other mechanisms. However, little is known about how stress signals are transmitted in the cell to lead to increased polyP accumulation. Previous work in the model enterobacterium Escherichia coli has indicated that the RNA polymerase-binding regulatory protein DksA is required for polyP synthesis in response to nutrient limitation stress. In this work, I set out to characterize the role of DksA in polyP regulation in more detail. I found that overexpression of DksA increases cellular polyP content (explaining the long-mysterious phenotype of dksA overexpression rescuing growth of a dnaK mutant at high temperatures) and characterized the roles of known functional residues of DksA in this process, finding that binding to RNA polymerase is required but that none of the other functions of DksA appear to be necessary. Transcriptomics revealed genome-wide transcriptional changes upon nutrient limitation, many of which were affected by DksA, and follow-up experiments identified complex interactions between DksA and the stress-sensing alternative sigma factors FliA, RpoN, and RpoE that impact polyP production, indicating that regulation of polyP synthesis is deeply entwined in the multifactorial stress response network of E. coli IMPORTANCE Inorganic polyphosphate (polyP) is an evolutionarily ancient, widely conserved biopolymer required for stress resistance and pathogenesis in diverse bacteria, but we do not understand how its synthesis is regulated. In this work, I gained new insights into this process by characterizing the role of the transcriptional regulator DksA in polyP regulation in Escherichia coli and identifying previously unknown links between polyP synthesis and the stress-responsive alternative sigma factors FliA, RpoN, and RpoE.

Proteomics of Brucella

Brucella spp. are Gram negative intracellular bacteria responsible for brucellosis, a worldwide distributed zoonosis. A prominent aspect of the Brucella life cycle is its ability to invade, survive and multiply within host cells. Comprehensive approaches, such as proteomics, have aided in unravelling the molecular mechanisms underlying Brucella pathogenesis. Technological and methodological advancements such as increased instrument performance and multiplexed quantification have broadened the range of proteome studies, enabling new and improved analyses, providing deeper and more accurate proteome coverage. Indeed, proteomics has demonstrated its contribution to key research questions in Brucella biology, i.e., immunodominant proteins, host-cell interaction, stress response, antibiotic targets and resistance, protein secretion. Here, we review the proteomics of Brucella with a focus on more recent works and novel findings, ranging from reconfiguration of the intracellular bacterial proteome and studies on proteomic profiles of Brucella infected tissues, to the identification of Brucella extracellular proteins with putative roles in cell signaling and pathogenesis. In conclusion, proteomics has yielded copious new candidates and hypotheses that require future verification. It is expected that proteomics will continue to be an invaluable tool for Brucella and applications will further extend to the currently ill-explored aspects including, among others, protein processing and post-translational modification.

Chemokine receptor 4 (CXCR4) blockade enhances resistance to bacterial internalization in RAW264.7 cells and AMD3100, a CXCR4 antagonist, attenuates susceptibility to Brucella abortus 544 infection in a murine model

We investigated the involvement of chemokine receptor type 4 (CXCR4) signaling on the outcome of Brucella (B.) abortus 544 infection in murine macrophages and in a mouse model. CXCR4 manipulation were first evaluated for Brucella invasion and intracellular survival efficiency, mitogen-activated protein kinases (ERK1/2, JNK, p38α) activation and generation of nitric oxide (NO), and then in the splenic bacterial proliferation and cytokine production in BALB/c mice. CXCR4 blockade is involved in the successful control of Brucella invasion, reduction of ERK1/2 phosphorylation and inhibition of nitric oxide release from macrophages. Furthermore, using a reported CXCR4-specific antagonist AMD3100 resulted in splenomegaly but attenuated Brucella proliferation in these organs with elevated serum levels of MCP-1, TNF and IL-12. These findings provide insights on the contribution of CXCR4 signaling in the phagocytic pathway and immune modulation during B. abortus infection.

Learning from the master: targets and functions of the CtrA response regulator in Brucella abortus and other alpha-proteobacteria

The α-proteobacteria are a fascinating group of free-living, symbiotic and pathogenic organisms, including the Brucella genus, which is responsible for a worldwide zoonosis. One common feature of α-proteobacteria is the presence of a conserved response regulator called CtrA, first described in the model bacterium Caulobacter crescentus, where it controls gene expression at different stages of the cell cycle. Here, we focus on Brucella abortus and other intracellular α-proteobacteria in order to better assess the potential role of CtrA in the infectious context. Comparative genomic analyses of the CtrA control pathway revealed the conservation of specific modules, as well as the acquisition of new factors during evolution. The comparison of CtrA regulons also suggests that specific clades of α-proteobacteria acquired distinct functions under its control, depending on the essentiality of the transcription factor. Other CtrA-controlled functions, for instance motility and DNA repair, are proposed to be more ancestral. Altogether, these analyses provide an interesting example of the plasticity of a regulation network, subject to the constraints of inherent imperatives such as cell division and the adaptations to diversified environmental niches.

Detection of Brucella spp. in dogs at Pantanal wetlands

Canine brucellosis is an infectious disease that produces reproductive disease in both males and females. Although Brucella canis is more common, the infection by Brucella abortus is more frequent in dogs sharing habitats with livestock and wild animals. We decided to investigate the role of dogs in the maintenance of Brucella spp. in the Pantanal wetland. Serum and whole blood samples were collected from 167 dogs. To detect antibodies against B. abortus and B. canis, buffered acidified plate antigen (BAPA) and agar gel immunodiffusion (AGID) tests were performed. To detect Brucella spp., B. abortus and B. canis DNA, PCR was performed using the bcsp31, BruAb2_0168, and BR00953 genes, respectively. To confirm the PCR results, three bcsp31 PCR products were sequenced and compared with sequences deposited in GenBank. The seropositivity rates of 7.8% and 9% were observed for the AGID and BAPA tests, respectively. Positivity rates of 45.5% and 10.8% were observed when testing bcsp31 and BruAb2_0168, respectively, while there was no positivity for BR00953. The sequenced products had 110 base pairs that aligned with 100% identity to B. abortus, B. canis, and B. suis. Considering our results, dogs may be acting as maintenance hosts of Brucella spp. in the Pantanal region.

Alterations of microRNAs and their predicted targeting mRNAs expression in RAW264.7 macrophages infected with Omp25 mutant Brucella melitensis

Brucellosis is a worldwide zoonosis caused by Brucella species and represents a serious threat to both human and animal health. Omp25 is an important immunogenic and protective antigen in Brucella species; however, the functional mechanism of Omp25 in macrophages has not yet been elucidated. Here, we constructed a Brucella melitensis omp25 deletion mutant (M5-90-Δomp25) and performed microRNA (miRNA) profiling of infected RAW264.7 cells. Eight differentially expressed miRNAs (mmu-miR-146a-5p, mmu-miR-155-5p, mmu-miR-3473a, mmu-miR-149-3p, mmu-miR-671-5p, mmu-miR-1224-5p, mmu-miR-1895, and mmu-miR-5126) were identified, with quantitative real-time PCR (qRT-PCR) analysis confirming the up-regulation of mmu-miR-146-a-5p and mmu-miR-155-5p and down-regulation of mmu-miR-149-3p and mmu-miR-5126. mRNA profiling of B. melitensis M5-90-Δomp25-infected RAW264.7 cells identified 967 differentially expressed genes (DEGs) (fold change ≥ 2). Among these, we focused on genes that were predicted by TargetScan, miRanda, and PicTar to be the potential targets of the differentially expressed miRNAs. The results suggested that 17 separate genes are potentially targeted by mmu-miR-149-3p, with one of these genes, Tbr1, also targeted by mmu-miR-5126. qRT-PCR analysis confirmed the up-regulation of nine of the predicted target genes. Our findings provide important information about the functional molecules in host cells, including miRNA and their target genes, affected by Omp25 from Brucella. This information is particularly valuable for the prophylaxis and treatment of brucellosis.

Global gene-expression profiles of intracellular survival of the BruAb2_1031 gene mutated Brucella abortus in professional phagocytes, RAW 264.7 cells

Background

Since recognizing the interaction between Brucella and host cells is crucial to the elucidation of the infectious process, Brucella researches have prioritized the investigation of genes related to pathogenicity. To demonstrate the roles of Brucella genes, RAW 264.7 cells were infected with the Brucella abortus wild-type and mutant strains (generated using transposon mutagenesis), after which the different transcriptional responses of the infected cells were determined using microarray.

Results

Following infection, enhanced strategies for intracellular survival, such as down-regulation of genes associated with cytokine responses and apoptosis, were observed in RAW 264.7 cells infected with C3 mutant strain when compared to the transcriptional responses of wild-type infected cells. Using sequence analysis, we determined the mutation site of a C3 mutant strain as the ATP-binding cassette transporter permease (BruAb2_1031). These results were evidenced by an increased level of intracellular survival of the C3 mutant strain.

Conclusions

Characteristics of each mutant strain including bacterial growth rate, abilities to induce cytokine production in macrophages after infection, internalization, and levels of intracellular survival and replication, were investigated by performing RAW 264.7 cell infection experiments. Our results indicate that the BruAb2_1031 gene might be closely related with intracellular survival of B. abortus in RAW 264.7 cells.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1223-7) contains supplementary material, which is available to authorized users.

Transposon Sequencing of Brucella abortus Uncovers Essential Genes for Growth In Vitro and Inside Macrophages

Brucella abortus is a class III zoonotic bacterial pathogen able to survive and replicate inside host cells, including macrophages. Here we report a multidimensional transposon sequencing analysis to identify genes essential for Brucella abortus growth in rich medium and replication in RAW 264.7 macrophages. The construction of a dense transposon mutant library and mapping of 929,769 unique mini-Tn5 insertion sites in the genome allowed identification of 491 essential coding sequences and essential segments in the B. abortus genome. Chromosome II carries a lower proportion (5%) of essential genes than chromosome I (19%), supporting the hypothesis of a recent acquisition of a megaplasmid as the origin of chromosome II. Temporally resolved transposon sequencing analysis as a function of macrophage infection stages identified 79 genes with a specific attenuation phenotype in macrophages, at either 2, 5, or 24 h postinfection, and 86 genes for which the attenuated mutant phenotype correlated with a growth defect on plates. We identified 48 genes required for intracellular growth, including the virB operon, encoding the type IV secretion system, which supports the validity of the screen. The remaining genes encode amino acid and pyrimidine biosynthesis, electron transfer systems, transcriptional regulators, and transporters. In particular, we report the need of an intact pyrimidine nucleotide biosynthesis pathway in order for B. abortus to proliferate inside RAW 264.7 macrophages.

Mutations in Escherichia coli Polyphosphate Kinase That Lead to Dramatically Increased In Vivo Polyphosphate Levels

Bacteria synthesize inorganic polyphosphate (polyP) in response to a wide variety of stresses, and production of polyP is essential for stress response and survival in many important pathogens and bacteria used in biotechnological processes. However, surprisingly little is known about the molecular mechanisms that control polyP synthesis. We have therefore developed a novel genetic screen that specifically links growth of Escherichia coli to polyP synthesis, allowing us to isolate mutations leading to enhanced polyP production. Using this system, we have identified mutations in the polyP-synthesizing enzyme polyP kinase (PPK) that lead to dramatic increases in in vivo polyP synthesis but do not substantially affect the rate of polyP synthesis by PPK in vitro These mutations are distant from the PPK active site and found in interfaces between monomers of the PPK tetramer. We have also shown that high levels of polyP lead to intracellular magnesium starvation. Our results provide new insights into the control of bacterial polyP accumulation and suggest a simple, novel strategy for engineering bacteria with increased polyP contents.IMPORTANCE PolyP is an ancient, universally conserved biomolecule and is important for stress response, energy metabolism, and virulence in a remarkably broad range of microorganisms. PolyP accumulation by bacteria is also important in biotechnology applications. For example, it is critical to enhanced biological phosphate removal (EBPR) from wastewater. Understanding how bacteria control polyP synthesis is therefore of broad importance in both the fields of bacterial pathogenesis and biological engineering. Using Escherichia coli as a model organism, we have identified the first known mutations in polyP kinase that lead to increases in cellular polyP content.

Expression, purification and immunochemical characterization of recombinant OMP28 protein of Brucella species

Brucellosis is the lion’s share of infectious disease of animals and it has a particular socio-economic importance for the Republic of Kazakhstan. Sixty percent of epizootic outbreaks of brucellosis identified in the Commonwealth of Independent States (CIS) originated from Kazakhstan in recent years. Definitive diagnosis of brucellosis remains a difficult task. Precisely for this reason, we evaluated a purified recombinant out membrane protein 28 (rOMP28) of Brucella species (Brucella spp.) produced in Escherichia coli (E. coli) as a diagnostic antigen in an Indirect ELISA (I-ELISA) for bovine brucellosis. The gene encoding OMP28 was synthesized using a two-round PCR procedure. In order to produce the rOMP28, the de novo synthesized DNA was cloned into the expression vector pET-22b(+). Then, the rOMP28 was expressed in E. coli system and characterized in the present study. We further estimated the diagnostic potential of purified rOMP28 of Brucella spp. for screening bovine sera. To determine if rOMP28 has a valuable benefit for use in the serodiagnosis of bovine brucellosis, rOMP28-based I-ELISA was performed. Brucella spp. positive (n=62) and Brucella spp. negative (n=28) samples from tube agglutination test (TAT) were positive (n=59) and negative (n=27) by I-ELISA, respectively. These findings show that the rOMP28 of Brucella spp. could be a good candidate for improving serological diagnostic methods for bovine brucellosis.

Early transcriptional responses of internalization defective Brucella abortus mutants in professional phagocytes, RAW 264.7

Background

Brucella abortus is an intracellular zoonotic pathogen which causes undulant fever, endocarditis, arthritis and osteomyelitis in human and abortion and infertility in cattle. This bacterium is able to invade and replicate in host macrophage instead of getting removed by this defense mechanism. Therefore, understanding the interaction between virulence of the bacteria and the host cell is important to control brucellosis. Previously, we generated internalization defective mutants and analyzed the envelope proteins. The present study was undertaken to evaluate the changes in early transcriptional responses between wild type and internalization defective mutants infected mouse macrophage, RAW 264.7.

Results

Both of the wild type and mutant infected macrophages showed increased expression levels in proinflammatory cytokines, chemokines, apoptosis and G-protein coupled receptors (Gpr84, Gpr109a and Adora2b) while the genes related with small GTPase which mediate intracellular trafficking was decreased. Moreover, cytohesin 1 interacting protein (Cytip) and genes related to ubiquitination (Arrdc3 and Fbxo21) were down-regulated, suggesting the survival strategy of this bacterium. However, we could not detect any significant changes in the mutant infected groups compared to the wild type infected group.

Conclusions

In summary, it was very difficult to clarify the alterations in host cellular transcription in response to infection with internalization defective mutants. However, we found several novel gene changes related to the GPCR system, ubiquitin-proteosome system, and growth arrest and DNA damages in response to B. abortus infection. These findings may contribute to a better understanding of the molecular mechanisms underlying host-pathogen interactions and need to be studied further.