Transposon mutagenesis of Rickettsia felis sca1 confers a distinct phenotype during flea infection.

Since its recognition in 1994 as the causative agent of human flea-borne spotted fever, Rickettsia felis, has been detected worldwide in over 40 different arthropod species. The cat flea, Ctenocephalides felis, is a well-described biological vector of R. felis. Unique to insect-borne rickettsiae, R. felis can employ multiple routes of infection including inoculation via salivary secretions and potentially infectious flea feces into the skin of vertebrate hosts. Yet, little is known of the molecular interactions governing flea infection and subsequent transmission of R. felis. While the obligate intracellular nature of rickettsiae has hampered the function of large-scale mutagenesis strategies, studies have shown the efficiency of mariner-based transposon systems in Rickettsiales. Thus, this study aimed to assess R. felis genetic mutants in a flea transmission model to elucidate genes involved in vector infection. A Himar1 transposase was used to generate R. felis transformants, in which subsequent genome sequencing revealed a transposon insertion near the 3' end of sca1. Alterations in sca1 expression resulted in unique infection phenotypes. While the R. felis sca1::tn mutant portrayed enhanced growth kinetics compared to R. felis wild-type during in vitro culture, rickettsial loads were significantly reduced during flea infection. As a consequence of decreased rickettsial loads within infected donor fleas, R. felis sca1::tn exhibited limited transmission potential. Thus, the use of a biologically relevant model provides evidence of a defective phenotype associated with R. felis sca1::tn during flea infection.

Examination of Rickettsial Host Range for Shuttle Vectors Based on dnaA and parA Genes from the pRM Plasmid of Rickettsia monacensis.

The genus Rickettsia encompasses a diverse group of obligate intracellular bacteria that are highly virulent disease agents of mankind as well as symbionts of arthropods. Native plasmids of Rickettsia amblyommatis (AaR/SC) have been used as models to construct shuttle vectors for genetic manipulation of several Rickettsia species. Here, we report on the isolation of the complete plasmid (pRM658B) from Rickettsia monacensis IrR/Munich mutant Rmona658B and the construction of shuttle vectors based on pRM. To identify regions essential for replication, we made vectors containing the dnaA and parA genes of pRM with various portions of the region surrounding these genes and a selection reporter cassette conferring resistance to spectinomycin and expression of green fluorescent protein. Rickettsia amblyommatis (AaR/SC), R. monacensis (IrR/Munich), Rickettsia bellii (RML 369-C), Rickettsia parkeri (Tate's Hell), and Rickettsia montanensis (M5/6) were successfully transformed with shuttle vectors containing pRM parA and dnaA. PCR assays targeting pRM regions not included in the vectors revealed that native pRM was retained in R. monacensis transformants. Determination of native pRM copy number using a plasmid-carried gene (RM_p5) in comparison to chromosomally carried gltA indicated reduced copy numbers in R. monacensis transformants. In transformed R. monacensis strains, native pRM and shuttle vectors with homologous parA and dnaA formed native plasmid-shuttle vector complexes. These studies provide insight on the maintenance of plasmids and shuttle vectors in rickettsiae. IMPORTANCERickettsia spp. are found in a diverse array of organisms, from ticks, mites, and fleas to leeches and insects. Many are not pathogenic, but others, such as Rickettsia rickettsii and Rickettsia prowazeckii, can cause severe illness or death. Plasmids are found in a large percentage of nonpathogenic rickettsiae, but not in species that cause severe disease. Studying these plasmids can reveal their role in the biology of these bacteria, as well as the molecular mechanism whereby they are maintained and replicate in rickettsiae. Here, we describe a new series of shuttle plasmids for the transformation of rickettsiae based on parA and dnaA sequences of plasmid pRM from Rickettsia monacensis. These shuttle vectors support transformation of diverse rickettsiae, including the native host of pRM, and are useful for investigating genetic determinants that govern rickettsial virulence or their ability to function as symbionts.

Growth Dynamics and Antibiotic Elimination of Symbiotic Rickettsia buchneri in the Tick Ixodes scapularis (Acari: Ixodidae).

Rickettsia buchneri is the principal symbiotic bacterium of the medically significant tick Ixodes scapularis This species has been detected primarily in the ovaries of adult female ticks and is vertically transmitted, but its tissue tropism in other life stages and function with regard to tick physiology is unknown. In order to determine the function of R. buchneri, it may be necessary to produce ticks free from this symbiont. We quantified the growth dynamics of R. buchneri naturally occurring in I. scapularis ticks throughout their life cycle and compared it with bacterial growth in ticks in which symbiont numbers were experimentally reduced or eliminated. To eliminate the bacteria, we exposed ticks to antibiotics through injection and artificial membrane feeding. Both injection and membrane feeding of the antibiotic ciprofloxacin were effective at eliminating R. buchneri from most offspring of exposed females. Because of its effectiveness and ease of use, we have determined that injection of ciprofloxacin into engorged female ticks is an efficient means of clearing R. buchneri from the majority of progeny.IMPORTANCE This paper describes the growth of symbiotic Rickettsia buchneri within Ixodes scapularis through the life cycle of the tick and provides methods to eliminate R. buchneri from I. scapularis ticks.

Disruption of VirB6 Paralogs in Anaplasma phagocytophilum Attenuates Its Growth.

Many pathogenic bacteria translocate virulence factors into their eukaryotic hosts by means of type IV secretion systems (T4SS) spanning the inner and outer membranes. Genes encoding components of these systems have been identified within the order Rickettsiales based upon their sequence similarities to other prototypical systems. Anaplasma phagocytophilum strains are obligate intracellular, tick-borne bacteria that are members of this order. The organization of these components at the genomic level was determined in several Anaplasma phagocytophilum strains, showing overall conservation, with the exceptions of the virB2 and virB6 genes. The virB6 loci are characterized by the presence of four virB6 copies (virB6-1 through virB6-4) arranged in tandem within a gene cluster known as the sodB-virB operon. Interestingly, the virB6-4 gene varies significantly in length among different strains due to extensive tandem repeats at the 3' end. To gain an understanding of how these enigmatic virB6 genes function in A. phagocytophilum, we investigated their expression in infected human and tick cells. Our results show that these genes are expressed by A. phagocytophilum replicating in both cell types and that VirB6-3 and VirB6-4 proteins are surface exposed. Analysis of an A. phagocytophilum mutant carrying the Himar1 transposon within the virB6-4 gene demonstrated that the insertion not only disrupted its expression but also exerted a polar effect on the sodB-virB operon. Moreover, the altered expression of genes within this operon was associated with the attenuated in vitro growth of A. phagocytophilum in human and tick cells, indicating the importance of these genes in the physiology of this obligate intracellular bacterium in such different environments.IMPORTANCE Knowledge of the T4SS is derived from model systems, such as Agrobacterium tumefaciens The structure of the T4SS in Rickettsiales differs from the classical arrangement. These differences include missing and duplicated components with structural alterations. Particularly, two sequenced virB6-4 genes encode unusual C-terminal structural extensions resulting in proteins of 4,322 (GenBank accession number AGR79286.1) and 9,935 (GenBank accession number ANC34101.1) amino acids. To understand how the T4SS is used in A. phagocytophilum, we describe the expression of the virB6 paralogs and explore their role as the bacteria replicate within its host cell. Conclusions about the importance of these paralogs for colonization of human and tick cells are supported by the deficient phenotype of an A. phagocytophilum mutant isolated from a sequence-defined transposon insertion library.

Multiple Ehrlichia chaffeensis Genes Critical for Its Persistent Infection in a Vertebrate Host Are Identified by Random Mutagenesis Coupled with In Vivo Infection Assessment.

Ehrlichia chaffeensis, a tick-transmitted obligate intracellular rickettsial agent, causes human monocytic ehrlichiosis. In recent reports, we described substantial advances in developing random and targeted gene disruption methods to investigate the functions of E. chaffeensis genes. We reported earlier that the Himar1 transposon-based random mutagenesis is a valuable tool in defining E. chaffeensis genes critical for its persistent growth in vivo in reservoir and incidental hosts. The method also aided in extending studies focused on vaccine development and immunity. Here, we describe the generation and mapping of 55 new mutations. To define the critical nature of the bacterial genes, infection experiments were carried out in the canine host with pools of mutant organisms. Infection evaluation in the physiologically relevant host by molecular assays and by xenodiagnoses allowed the identification of many proteins critical for the pathogen's persistent in vivo growth. Genes encoding proteins involved in biotin biosynthesis, protein synthesis and fatty acid biosynthesis, DNA repair, electron transfer, and a component of a multidrug resistance (MDR) efflux pump were concluded to be essential for the pathogen's in vivo growth. Three known immunodominant membrane proteins, i.e., two 28-kDa outer membrane proteins (P28/OMP) and a 120-kDa surface protein, were also recognized as necessary for the pathogen's obligate intracellular life cycle. The discovery of many E. chaffeensis proteins crucial for its continuous in vivo growth will serve as a major resource for investigations aimed at defining pathogenesis and developing novel therapeutics for this and related pathogens of the rickettsial family Anaplasmataceae.

Ehrlichia Isolate from a Minnesota Tick: Characterization and Genetic Transformation.

Ehrlichia muris subsp. eauclairensis is recognized as the etiological agent of human ehrlichiosis in Minnesota and Wisconsin. We describe the culture isolation of this organism from a field-collected tick and detail its relationship to other species of Ehrlichia The isolate could be grown in a variety of cultured cell lines and was effectively transmitted between Ixodes scapularis ticks and rodents, with PCR and microscopy demonstrating a broad pattern of dissemination in arthropod and mammalian tissues. Conversely, Amblyomma americanum ticks were not susceptible to infection by the Ehrlichia Histologic sections further revealed that the wild-type isolate was highly virulent for mice and hamsters, causing severe systemic disease that was frequently lethal. A Himar1 transposase system was used to create mCherry- and mKate-expressing EmCRT mutants, which retained the ability to infect rodents and ticks.IMPORTANCE Ehrlichioses are zoonotic diseases caused by intracellular bacteria that are transmitted by ixodid ticks. Here we report the culture isolation of bacteria which are closely related to, or the same as the Ehrlichia muris subsp. eauclairensis, a recently recognized human pathogen. EmCRT, obtained from a tick removed from deer at Camp Ripley, MN, is the second isolate of this subspecies described and is distinctive in that it was cultured directly from a field-collected tick. The isolate's cellular tropism, pathogenic changes caused in rodent tissues, and tick transmission to and from rodents are detailed in this study. We also describe the genetic mutants created from the EmCRT isolate, which are valuable tools for the further study of this intracellular pathogen.

An O-Methyltransferase Is Required for Infection of Tick Cells by Anaplasma phagocytophilum.

Anaplasma phagocytophilum, the causative agent of Human Granulocytic Anaplasmosis (HGA), is an obligately intracellular α-proteobacterium that is transmitted by Ixodes spp ticks. However, the pathogen is not transovarially transmitted between tick generations and therefore needs to survive in both a mammalian host and the arthropod vector to complete its life cycle. To adapt to different environments, pathogens rely on differential gene expression as well as the modification of proteins and other molecules. Random transposon mutagenesis of A. phagocytophilum resulted in an insertion within the coding region of an o-methyltransferase (omt) family 3 gene. In wild-type bacteria, expression of omt was up-regulated during binding to tick cells (ISE6) at 2 hr post-inoculation, but nearly absent by 4 hr p.i. Gene disruption reduced bacterial binding to ISE6 cells, and the mutant bacteria that were able to enter the cells were arrested in their replication and development. Analyses of the proteomes of wild-type versus mutant bacteria during binding to ISE6 cells identified Major Surface Protein 4 (Msp4), but also hypothetical protein APH_0406, as the most differentially methylated. Importantly, two glutamic acid residues (the targets of the OMT) were methyl-modified in wild-type Msp4, whereas a single asparagine (not a target of the OMT) was methylated in APH_0406. In vitro methylation assays demonstrated that recombinant OMT specifically methylated Msp4. Towards a greater understanding of the overall structure and catalytic activity of the OMT, we solved the apo (PDB_ID:4OA8), the S-adenosine homocystein-bound (PDB_ID:4OA5), the SAH-Mn2+ bound (PDB_ID:4PCA), and SAM- Mn2+ bound (PDB_ID:4PCL) X-ray crystal structures of the enzyme. Here, we characterized a mutation in A. phagocytophilum that affected the ability of the bacteria to productively infect cells from its natural vector. Nevertheless, due to the lack of complementation, we cannot rule out secondary mutations.

Proposal to reclassify Ehrlichia muris as Ehrlichia muris subsp. muris subsp. nov. and description of Ehrlichia muris subsp. eauclairensis subsp. nov., a newly recognized tick-borne pathogen of humans.

We have previously described a novel taxon of the genus Ehrlichia (type strain WisconsinT), closely related to Ehrlichia muris, that causes human ehrlichiosis among patients with exposures to ticks in the upper midwestern USA. DNA from this bacterium was also detected in Ixodes scapularis and Peromyscus leucopus collected in Minnesota and Wisconsin. To determine the relationship between the E. muris-like agent (EMLA) and other species of the genus Ehrlichia phenotypic, genotypic and epidemiologic comparisons were undertaken, including sequence analysis of eight gene loci (3906 nucleotides) for 39 EMLA DNA samples and the type strain of E. muris AS145T. Three loci were also sequenced from DNA of nine strains of E. muris from mouse spleens from Japan. All sequences from E. muris were distinct from homologous EMLA sequences, but differences between them were less than those observed among other species of the genus Ehrlichia. Phenotypic comparison of EMLA and E. muris revealed similar culture and electron microscopic characteristics, but important differences were noted in their geographic distribution, ecological associations and behavior in mouse models of infection. Based on these comparisons, we propose that type strain WisconsinT represents a novel subspecies, Ehrlichia murissubsp. eauclairensis,subsp. nov. This strain is available through the Centers for Disease Control and Prevention Rickettsial Isolate Reference Collection (CRIRC EMU002T) and through the Collection de Souches de l'Unité des Rickettsies (CSURP2883 T). The subspecies Ehrlichia murissubsp. muris subsp. nov. is automatically created and the type strain AS145T is also available through the same collections (CRIRC EMU001T, CSUR E2T). Included is an emended description of E. muris.

Infection of Immature Ixodes scapularis (Acari: Ixodidae) by Membrane Feeding.

A reduction in the use of animals in infectious disease research is desirable for animal welfare as well as for simplification and standardization of experiments. An artificial silicone-based membrane-feeding system was adapted for complete engorgement of adult and nymphal Ixodes scapularis Say (Acari: Ixodidae), and for infecting nymphs with pathogenic, tick-borne bacteria. Six wild-type and genetically transformed strains of four species of bacteria were inoculated into sterile bovine blood and fed to ticks. Pathogens were consistently detected in replete nymphs by polymerase chain reaction. Adult ticks that ingested bacteria as nymphs were evaluated for transstadial transmission. Borrelia burgdorferi and Ehrlichia muris-like agent showed high rates of transstadial transmission to adult ticks, whereas Anaplasma phagocytophilum and Rickettsia monacensis demonstrated low rates of transstadial transmission/maintenance. Artificial membrane feeding can be used to routinely maintain nymphal and adult I. scapularis, and infect nymphs with tick-borne pathogens.

Targeted and random mutagenesis of Ehrlichia chaffeensis for the identification of genes required for in vivo infection.

Ehrlichia chaffeensis is a tick transmitted pathogen responsible for the disease human monocytic ehrlichiosis. Research to elucidate gene function in rickettsial pathogens is limited by the lack of genetic manipulation methods. Mutational analysis was performed, targeting to specific and random insertion sites within the bacterium's genome. Targeted mutagenesis at six genomic locations by homologous recombination and mobile group II intron-based methods led to the consistent identification of mutants in two genes and in one intergenic site; the mutants persisted in culture for 8 days. Three independent experiments using Himar1 transposon mutagenesis of E. chaffeensis resulted in the identification of multiple mutants; these mutants grew continuously in macrophage and tick cell lines. Nine mutations were confirmed by sequence analysis. Six insertions were located within non-coding regions and three were present in the coding regions of three transcriptionally active genes. The intragenic mutations prevented transcription of all three genes. Transposon mutants containing a pool of five different insertions were assessed for their ability to infect deer and subsequent acquisition by Amblyomma americanum ticks, the natural reservoir and vector, respectively. Three of the five mutants with insertions into non-coding regions grew well in deer. Transposition into a differentially expressed hypothetical gene, Ech_0379, and at 18 nucleotides downstream to Ech_0230 gene coding sequence resulted in the inhibition of growth in deer, which is further evidenced by their failed acquisition by ticks. Similarly, a mutation into the coding region of ECH_0660 gene inhibited the in vivo growth in deer. This is the first study evaluating targeted and random mutagenesis in E. chaffeensis, and the first to report the generation of stable mutants in this obligate intracellular bacterium. We further demonstrate that in vitro mutagenesis coupled with in vivo infection assessment is a successful strategy in identifying genomic regions required for the pathogen's in vivo growth.

Reduced Infectivity in cattle for an outer membrane protein mutant of Anaplasma marginale.

Anaplasma marginale is the causative agent of anaplasmosis in cattle. Transposon mutagenesis of this pathogen using the Himar1 system resulted in the isolation of an omp10 operon insertional mutant referred to as the omp10::himar1 mutant. The work presented here evaluated if this mutant had morphological and/or growth rate defects compared to wild-type A. marginale. Results showed that the morphology, developmental cycle, and growth in tick and mammalian cell cultures are similar for the mutant and the wild type. Tick transmission experiments established that tick infection levels with the mutant were similar to those with wild-type A. marginale and that infected ticks successfully infected cattle. However, this mutant exhibited reduced infectivity and growth in cattle. The possibility of transforming A. marginale by transposon mutagenesis coupled with in vitro and in vivo assessment of altered phenotypes can aid in the identification of genes associated with virulence. The isolation of deliberately attenuated organisms that can be evaluated in their natural biological system is an important advance for the rational design of vaccines against this species.

Transmission of Anaplasma phagocytophilum from endothelial cells to peripheral granulocytes in vitro under shear flow conditions.

Anaplasma phagocytophilum (Ap) is a tick-borne pathogen, which can cause granulocytic anaplasmosis in humans and animals. In vivo this obligate intracellular pathogen is primarily located in circulating mature granulocytes, but it also infects endothelial cells. In order to study the interaction between Ap-infected endothelial cells and human granulocytes under conditions similar to those found naturally in the infected host, an in vitro model that mimics physiological flow conditions in the microvasculature was established. Cell-to-cell interactions were then visualized by microscopy, which showed that granulocytes adhered strongly to Ap-infected endothelial cells at a shear stress of 0.5 dyne/cm(2). In addition, Ap-transmission assays under flow conditions showed that the bacteria transferred from infected endothelial cells to circulating granulocytes and were able to establish infection in constantly moving granulocytes. Cell surface analysis showed that Ap induced up-regulation of the cell adhesion molecules ICAM-1 and VCAM-1 on infected endothelial cells in a dose-dependent manner. Furthermore, IL-8 secretion by endothelial cells indicated that the presence of Ap induced a pro-inflammatory response. In summary, the results of this study suggest that endothelial cells of the microvasculature (1) provide an excellent site for Ap dissemination to peripheral blood granulocytes under flow conditions and therefore may play a crucial role in the development of persistent infection, and (2) are stimulated by Ap to express surface molecules and cytokines that may lead to inflammatory responses at the site of the infection.

Rickettsia buchneri sp. nov., a rickettsial endosymbiont of the blacklegged tick Ixodes scapularis.

We obtained a rickettsial isolate from the ovaries of the blacklegged tick, Ixodes scapularis. The isolate (ISO7(T)) was grown in the Ixodes ricinus embryonic cell line IRE11. We characterized the isolate by transmission electron microscopy and gene sequencing. Phylogenetic analysis of 11 housekeeping genes demonstrated that the isolate fulfils the criteria to be classified as a representative of a novel rickettsial species closely related to 'Rickettsia monacensis'. These rickettsiae form a clade separate from other species of rickettsiae. Gene sequences indicated that several genes important in rickettsial motility, invasiveness and temperature adaptation were mutated (e.g. sca2, rickA, hsp22, pldA and htrA). We propose the name Rickettsia buchneri sp. nov. for this bacterium that infects the ovaries of the tick I. scapularis to acknowledge the pioneering contributions of Professor Paul Buchner (1886-1978) to research on bacterial symbionts. The type strain of R. buchneri sp. nov. is strain ISO-7(T) ( = DSM 29016(T) = ATCC VR-1814(T)).

An Ixodes scapularis cell line with a predominantly neuron-like phenotype.

The Ixodes scapularis embryo-derived cell line ISE6 is the most widely utilized tick-derived cell line due to its susceptibility to a wide variety of tick- and non-tick-vectored pathogens. Little is known about its tissue origin or biological background. Protein expression of ISE6 cells was compared with that of another I. scapularis-derived cell line, IDE12, and dissected tick synganglia. Results demonstrated the presence of a neuronal marker protein, type 3 ß-tubulin, in all three samples, as well as other shared and unique neuronal and immune response-associated proteins. Of neuronal proteins shared between the two cell lines, ISE6 expressed several in significantly greater quantities than IDE12. Stimulation of ISE6 cells by in vivo exposure to the hemocoel environment in unfed larval and molting nymphal ticks, but not unfed nymphal ticks, resulted in the development of neuron-like morphologic characteristics in the implanted cells.

Knockout of an outer membrane protein operon of Anaplasma marginale by transposon mutagenesis.

BACKGROUND: The large amounts of data generated by genomics, transcriptomics and proteomics have increased our understanding of the biology of Anaplasma marginale. However, these data have also led to new assumptions that require testing, ideally through classical genetic mutation. One example is the definition of genes associated with virulence. Here we describe the molecular characterization of a red fluorescent and spectinomycin and streptomycin resistant A. marginale mutant generated by Himar1 transposon mutagenesis. RESULTS: High throughput genome sequencing to determine the Himar1-A. marginale genome junctions established that the transposon sequences were integrated within the coding region of the omp10 gene. This gene is arranged within an operon with AM1225 at the 5' end and with omp9, omp8, omp7 and omp6 arranged in tandem at the 3' end. RNA analysis to determine the effects of the transposon insertion on the expression of omp10 and downstream genes revealed that the Himar1 insertion not only reduced the expression of omp10 but also that of downstream genes. Transcript expression from omp9, and omp8 dropped by more than 90% in comparison with their counterparts in wild-type A. marginale. Immunoblot analysis showed a reduction in the production of Omp9 protein in these mutants compared to wild-type A. marginale. CONCLUSIONS: These results demonstrate that transposon mutagenesis in A. marginale is possible and that this technology can be used for the creation of insertional gene knockouts that can be evaluated in natural host-vector systems.

Emergence of a new pathogenic Ehrlichia species, Wisconsin and Minnesota, 2009.

BACKGROUND: Ehrlichiosis is a clinically important, emerging zoonosis. Only Ehrlichia chaffeensis and E. ewingii have been thought to cause ehrlichiosis in humans in the United States. Patients with suspected ehrlichiosis routinely undergo testing to ensure proper diagnosis and to ascertain the cause. METHODS: We used molecular methods, culturing, and serologic testing to diagnose and ascertain the cause of cases of ehrlichiosis. RESULTS: On testing, four cases of ehrlichiosis in Minnesota or Wisconsin were found not to be from E. chaffeensis or E. ewingii and instead to be caused by a newly discovered ehrlichia species. All patients had fever, malaise, headache, and lymphopenia; three had thrombocytopenia; and two had elevated liver-enzyme levels. All recovered after receiving doxycycline treatment. At least 17 of 697 Ixodes scapularis ticks collected in Minnesota or Wisconsin were positive for the same ehrlichia species on polymerase-chain-reaction testing. Genetic analyses revealed that this new ehrlichia species is closely related to E. muris. CONCLUSIONS: We report a new ehrlichia species in Minnesota and Wisconsin and provide supportive clinical, epidemiologic, culture, DNA-sequence, and vector data. Physicians need to be aware of this newly discovered close relative of E. muris to ensure appropriate testing, treatment, and regional surveillance. (Funded by the National Institutes of Health and the Centers for Disease Control and Prevention.).

Motility characteristics are altered for Rickettsia bellii transformed to overexpress a heterologous rickA gene.

The rickettsial protein RickA activates host cell factors associated with the eukaryotic actin cytoskeleton and is likely involved with rickettsial host cell binding and infection and the actin-based motility of spotted fever group rickettsiae. The rickA gene sequence and protein vary substantially between Rickettsia species, as do observed motility-associated phenotypes. To help elucidate the function of RickA and determine the effects of species-specific RickA variations, we compared extracellular binding, intracellular motility, and intercellular spread phenotypes of three Rickettsia bellii variants. These included two shuttle vector-transformed R. bellii strains and the wild-type isolate from which they were derived, R. bellii RML 369C. Both plasmid shuttle vectors carried spectinomycin resistance and a GFPuv reporter; one contained Rickettsia monacensis-derived rickA, and the other lacked the rickA gene. Rickettsia bellii transformed to express R. monacensis rickA highly overexpressed this transcript in comparison to its native rickA. These rickettsiae also moved at higher velocities and followed a more curved path than the negative-control transformants. A lower proportion of R. monacensis rickA-expressing bacteria ever became motile, however, and they formed smaller plaques.

The role of autophagy in tick-endosymbiont interactions: insights from Ixodes scapularis and Rickettsia buchneri.

IMPORTANCE: Ticks are second only to mosquitoes in their importance as vectors of disease agents; however, tick-borne diseases (TBDs) account for the majority of all vector-borne disease cases in the United States (approximately 76.5%), according to Centers for Disease Control and Prevention reports. Newly discovered tick species and their associated disease-causing pathogens, and anthropogenic and demographic factors also contribute to the emergence and re-emergence of TBDs. Thus, incorporating different tick control approaches based on a thorough knowledge of tick biology has great potential to prevent and eliminate TBDs in the future. Here we demonstrate that replication of a transovarially transmitted rickettsial endosymbiont depends on the tick's autophagy machinery but not on apoptosis. Our findings improve our understanding of the role of symbionts in tick biology and the potential to discover tick control approaches to prevent or manage TBDs.

An Anaplasma phagocytophilum T4SS effector, AteA, is essential for tick infection.

Pathogens must adapt to disparate environments in permissive host species, a feat that is especially pronounced for vector-borne microbes, which transition between vertebrate hosts and arthropod vectors to complete their lifecycles. Most knowledge about arthropod-vectored bacterial pathogens centers on their life in the mammalian host, where disease occurs. However, disease outbreaks are driven by the arthropod vectors. Adapting to the arthropod is critical for obligate intracellular rickettsial pathogens, as they depend on eukaryotic cells for survival. To manipulate the intracellular environment, these bacteria use Type IV Secretion Systems (T4SS) to deliver effectors into the host cell. To date, few rickettsial T4SS translocated effectors have been identified and have only been examined in the context of mammalian infection. We identified an effector from the tick-borne rickettsial pathogen Anaplasma phagocytophilum , HGE1_02492, as critical for survival in tick cells and acquisition by ticks in vivo . Conversely, HGE1_02492 was dispensable during mammalian cell culture and murine infection. We show HGE1_02492 is translocatable in a T4SS-dependent manner to the host cell cytosol. In eukaryotic cells, the HGE1_02492 localized with cortical actin filaments, which is dependent on multiple sub-domains of the protein. HGE1_02492 is the first arthropod-vector specific T4SS translocated effector identified from a rickettsial pathogen. Moreover, the subcellular target of HGE1_02492 suggests that A. phagocytophilum is manipulating actin to enable arthropod colonization. Based on these findings, we propose the name AteA for Anaplasma ( phagocytophilum ) tick effector A. Altogether, we show that A. phagocytophilum uses distinct strategies to cycle between mammals and arthropods. Importance: Ticks are the number one vector of pathogens for livestock worldwide and for humans in the US. The biology of tick transmission is an understudied area. Understanding this critical interaction could provide opportunities to affect the course of disease spread. In this study we examined the zoonotic tick-borne agent Anaplasma phagocytophilum and identified a secreted protein, AteA, that is expressed in a tick-specific manner. These secreted proteins, termed effectors, are the first proteins to interact with the host environment. AteA is essential for survival in ticks and appears to interact with cortical actin. Most effector proteins are studied in the context of the mammalian host; however, understanding how this unique set of proteins affect tick transmission is critical to developing interventions.