Endosymbiont CLS-HI plays a role in reproduction and development of Haemaphysalis longicornis

Disruption of bacterial interactions and community assembly in Babesia-infected Haemaphysalis longicornis following antibiotic treatment

BACKGROUND

A previous study highlighted the role of antibiotic-induced dysbiosis in the tick microbiota, facilitating the transstadial transmission of Babesia microti from nymph to adult in Haemaphysalis longicornis. This study builds on previous findings by analyzing sequence data from an earlier study to investigate bacterial interactions that could be linked to enhanced transstadial transmission of Babesia in ticks. The study employed antibiotic-treated (AT) and control-treated (CT) Haemaphysalis longicornis ticks to investigate shifts in microbial community assembly. Network analysis techniques were utilized to assess bacterial interactions, comparing network centrality measures between AT and CT groups, alongside studying network robustness and connectivity loss. Additionally, functional profiling was conducted to evaluate metabolic diversity in response to antibiotic treatment.

RESULTS

The analysis revealed notable changes in microbial community assembly in response to antibiotic treatment. Antibiotic-treated (AT) ticks displayed a greater number of connected nodes but fewer correlations compared to control-treated (CT) ticks, indicating a less interactive yet more connected microbial community. Network centrality measures such as degree, betweenness, closeness, and eigenvector centrality, differed significantly between AT and CT groups, suggesting alterations in local network dynamics due to antibiotic intervention. Coxiella and Acinetobacter exhibited disrupted connectivity and roles, with the former showing reduced interactions in AT group and the latter displaying a loss of connected nodes, emphasizing their crucial roles in microbial network stability. Robustness tests against node removal showed decreased stability in AT networks, particularly under directed attacks, confirming a susceptibility of the microbial community to disturbances. Functional profile analysis further indicated a higher diversity and richness in metabolic capabilities in the AT group, reflecting potential shifts in microbial metabolism as a consequence of antimicrobial treatment.

CONCLUSIONS

Our findings support that bacterial interaction traits boosting the transstadial transmission of Babesia could be associated with reduced colonization resistance. The disrupted microbial interactions and decreased network robustness in AT ticks suggest critical vulnerabilities that could be targeted for managing tick-borne diseases.

Nutritional symbiosis in ticks: singularities of the genus Ixodes

Symbiosis with intracellular bacteria is essential for the nutrition of ticks, particularly through the biosynthesis of B vitamins. Yet, ticks of the genus Ixodes, which include major vectors of human pathogens, lack the nutritional symbionts usually found in other tick genera. This paradox raises questions about the mechanisms that Ixodes ticks use to prevent nutritional deficiencies. Nonetheless, Ixodes ticks commonly harbor other symbionts belonging to the order Rickettsiales. Although these obligate intracellular bacteria are primarily known as human pathogens, Rickettsiales symbionts often dominate the Ixodes microbial community without causing diseases. They also significantly influence Ixodes physiology, synthesize key B vitamins, and are crucial for immatures. These findings underscore unique associations between Rickettsiales and Ixodes ticks distinct from other tick genera.

Molecular and next-generation sequencing analysis of tick-borne pathogens of Rhipicephalus ticks (Acari: Ixodidae) in cattle and dogs

Ticks are small and adaptable arachnid ectoparasites and global carriers of various pathogens that threaten both human and animal health. They are present in many parts of China. A total of 858 ticks were collected from various regions and hosts, then subjected to species identification based on morphological and molecular characteristics, as described in the authors' previous study. Eighty-three individual tick samples were selected for screening pathogens based on metagenomic next-generation sequencing (mNGS) and polymerase chain reaction (PCR) assays. The genomic DNA of tick species was extracted, and amplification of the bacterial 16S rRNA gene was carried out from DNA of individual ticks using V3-V4 hypervariable regions, before subjecting to metagenomic analysis. Each tick underwent specific PCR tests for identifying the bacterial species present, including Anaplasma, Ehrlichia, Coxiella, and Rickettsia, and also protozoans such as Babesia, Theileria, and Hepatozoon. Illumina NovaSeq sequencing results revealed that the dominant phylum and family in Rhipicephalus spp. were Bacteroidota and Muribaculaceae, respectively. Alpha diversity patterns varied depending on tick sex (R. linnaei only), species and location, but not on host. Furthermore, bacterial pathogens, including A. marginale (58 %, 29/50), A. platys (6 %, 3/50), E. minasensis (2 %, 1/50), Ehrlichia sp. (10 %, 5/50), T. sinensis (24 %, 12/50), T. orientalis (54 %, 27/50) and Coxiella-like bacteria (CLB) (80 %, 40/50) were detected in R. microplus, while E. canis (33.33 %, 10/30), H. canis (20 %, 6/30) and CLB (100 %, 30/30) were detected in R. linnaei. Also, Anaplasma sp. (33.33 %, 1/3), A. marginale (33.33 %, 1/3), R. felis (33.33 %, 1/3) and CLB (100 %, 3/3) were detected in R. haemaphysaloides. Dual and triple co-infections involving pathogens or CLB were detected in 84.00 % of R. microplus, 66.66 % of R. haemaphysaloides, and 33.00 % of R. linnaei. The report on microbial communities and pathogens, which found from Rhipicephalus spp. in Hainan Island, is an important step towards a better understanding of tick-borne disease transmission. This is the first report in the area on the presence of Anaplasma sp., A. marginale, R. felis and Coxiella, in R. haemaphysaloides.

Tick symbiosis

As obligate blood-feeders, ticks serve as vectors for a variety of pathogens that pose threats on both human and livestock health. The microbiota that ticks harbor play important roles in influencing tick nutrition, development, reproduction, and vector. These microbes also affect the capacity of ticks to transmit pathogens (vector competence). Therefore, comprehending the functions of tick microbiota will help in developing novel and effective tick control strategies. Here, we summarize the effects of main tick symbiotic bacteria on tick physiology and vector competency.

Severe fever with thrombocytopenia syndrome virus infection shapes gut microbiome of the tick vector Haemaphysalis longicornis

BACKGROUND

Ticks serve as vectors for a diverse array of pathogens, including viruses responsible for both human and livestock diseases. Symbiotic bacteria hold significant potential for controlling tick-borne disease. However, the alteration of tick gut bacterial community in response to pathogen infection has not been analyzed for any tick-borne viruses. Here, the impact of severe fever with thrombocytopenia syndrome virus (SFTSV) infection on bacterial diversity in the gut of Haemaphysalis longicornis is investigated.

METHODS

Unfed tick females were artificially infected with SFTSV. The gut samples were collected and the genomic DNA was extracted. We then investigated alterations in gut bacterial composition in response to SFTSV infection through 16S rRNA gene sequencing.

RESULTS

The study found that a reduction in the number of operational taxonomic units (OTUs) in the tick gut following SFTSV infection. However, there were no significant changes in alpha diversity indices upon infection. Four genera, including Corynebacterium, Arthrobacter, Sphingomonas, and Escherichia, were identified as biomarkers for the tick gut without SFTSV infection. Notably, the predicted correlation network indicated that the biomarkers Sphingomonas and Escherichia exhibited positive correlations within the same subcommunity, which was altered upon viral infection.

CONCLUSIONS

These findings revealed that the change in tick gut bacterial composition upon SFTSV infection and could facilitate the discovery new target for tick-borne viral disease control.

Tetracycline inhibits tick host reproduction by modulating bacterial microbiota, gene expression and metabolism levels

BACKGROUND

Ticks are disease vectors that are a matter of worldwide concern. Antibiotic treatments have been used to explore the interactions between ticks and their symbiotic microorganisms. In addition to altering the host microbial community, antibiotics can have toxic effects on the host.

RESULTS

In the tick Haemaphysalis longicornis, engorged females showed reproductive disruption after microinjection of tetracycline. Multi-omics approaches were implemented to unravel the mechanisms of tick reproductive inhibition in this study. There were no significant changes in bacterial density in the whole ticks on Day (D)2 or D4 after tetracycline treatment, whereas the bacterial microbial community was significantly altered, especially on D4. The relative abundances of the bacteria Staphylococcus, Bacillus and Pseudomonas decreased after tetracycline treatment, whereas the relative abundances of Coxiella and Rhodococcus increased. Ovarian transcriptional analysis revealed a cumulative effect of tetracycline treatment, as there was a significant increase in the number of differentially expressed genes with treatment time and a higher number of downregulated genes. The tick physiological pathways including lysosome, extracellular matrix (ECM)-receptor interaction, biosynthesis of ubiquinone and other terpenoids-quinones, insect hormone biosynthesis, and focal adhesion were significantly inhibited after 4 days of tetracycline treatment. Metabolite levels were altered after tetracycline treatment and the differences increased with treatment time. The differential metabolites were involved in a variety of physiological pathways; the downregulated metabolites were significantly enriched in the nicotinate and nicotinamide metabolism, galactose metabolism, and ether lipid metabolism pathways.

CONCLUSIONS

These findings indicate that tetracycline inhibits tick reproduction through the regulation of tick bacterial communities, gene expression and metabolic levels. The results may provide new strategies for tick control. © 2023 Society of Chemical Industry.

Mechanism of the toxic effects of tetracycline on blood meal digestion in Haemaphysalis longicornis

The extensive utilization of antibiotics in the field of animal husbandry gives rise to various concerns pertaining to the environment and human health. Here, we demonstrate that the administration of tetracycline impedes blood meal digestion in the tick Haemaphysalis longicornis. Tissue sectioning, 16S rRNA high-throughput sequencing, and transcriptome sequencing of the midgut were employed to elucidate the mechanism underlying tetracycline toxicity. The treatment group consisted of engorged female ticks that were subjected to tetracycline microinjections (75 µg per tick), whereas the control group received sterile water injections. On days 2 and 4 following the injections, the tick body weight changes were assessed and the midguts were dissected and processed. Change in tick body weight in tetracycline-treated group was less than in the control group. In tetracycline-treated ticks, midgut epithelial cells were loosely connected and blood meal digestion was impaired compared to the control group. There was no significant change in midgut bacterial diversity after tetracycline treatment. On day 2 following treatment, the relative abundance of Escherichia-Shigella was significantly decreased, whereas the relative abundance of Allorhizobium was significantly increased compared to the control group. On day 4 following treatment, the relative abundance of Escherichia-Shigella, Allorhizobium, Ochrobactrum, and Acidibacter decreased significantly, whereas the relative abundance of Paraburkholderia and Pelomonas increased significantly. Tetracycline treatment also affected midgut gene expression, producing a cumulative effect wherein the differentially expressed genes (DEGs) were mostly down-regulated. KEGG enrichment pathway analysis revealed that on day 2 the up-regulated DEGs were significantly enriched in 21 pathways, including apoptosis and phagosome. Comparatively, the down-regulated DEGs were significantly enriched in 26 pathways, including N-glycan biosynthesis, lysosome, and autophagy. In contrast, on day 4 the up-regulated DEGs were significantly enriched in 10 pathways including aminoacyl-tRNA biosynthesis, ribosome biogenesis, RNA transport, and DNA replication, whereas the down-regulated differential genes were significantly enriched in 11 pathways including lysosome, peroxisome, N-glycan biosynthesis, and fatty acid synthesis. This indicates that tetracycline injection inhibited blood meal digestion by affecting midgut digestive cells, gut flora diversity, and gene expression. These findings could contribute to tick control by inhibiting blood meal digestion.

Analysis of the bacterial community in female Rhipicephalus microplus ticks from selected provinces in Luzon, Philippines, using next-generation sequencing

Analysis of the tick microbiome can help understand tick-symbiont interactions and identify undiscovered pathogens, which may aid in implementing control of ticks and tick-borne diseases. The tropical cattle tick Rhipicephalus microplus is a widespread ectoparasite of cattle in the Philippines, negatively affecting animal productivity and health. This study characterized the bacterial community of R. microplus from Luzon, Philippines, through next-generation sequencing of 16s rRNA. DNA was extracted from 45 partially engorged female ticks from nine provinces. The DNA samples were pooled per province and then sequenced and analyzed using an open-source bioinformatics platform. In total, 667 operational taxonomic units (OTUs) were identified. The ticks in all nine provinces were found to have Coxiella, Corynebacterium, Staphylococcus, and Acinetobacter. Basic local alignment search tool (BLAST) analysis revealed the presence of known pathogens of cattle, such as Bartonella, Ehrlichia minasensis, and Dermatophilus congolensis. The tick samples from Laguna, Quezon, and Batangas had the most diverse bacterial species, whereas the tick samples from Ilocos Norte had the lowest diversity. Similarities in the composition of the bacterial community in ticks from provinces near each other were also observed. This is the first study on metagenomic analysis of cattle ticks in the Philippines, providing new insights that may be useful for controlling ticks and tick-borne diseases.

Microbiota in disease-transmitting vectors

Haematophagous arthropods, including mosquitoes, ticks, flies, triatomine bugs and lice (here referred to as vectors), are involved in the transmission of various pathogens to mammals on whom they blood feed. The diseases caused by these pathogens, collectively known as vector-borne diseases (VBDs), threaten the health of humans and animals. Although the vector arthropods differ in life histories, feeding behaviour as well as reproductive strategies, they all harbour symbiotic microorganisms, known as microbiota, on which they depend for completing essential aspects of their biology, such as development and reproduction. In this Review, we summarize the shared and unique key features of the symbiotic associations that have been characterized in the major vector taxa. We discuss the crosstalks between microbiota and their arthropod hosts that influence vector metabolism and immune responses relevant for pathogen transmission success, known as vector competence. Finally, we highlight how current knowledge on symbiotic associations is being explored to develop non-chemical-based alternative control methods that aim to reduce vector populations, or reduce vector competence. We conclude by highlighting the remaining knowledge gaps that stand to advance basic and translational aspects of vector-microbiota interactions.

Impact of endosymbionts on tick physiology and fitness

Ticks transmit pathogens and harbour non-pathogenic, vertically transmitted intracellular bacteria termed endosymbionts. Almost all ticks studied to date contain 1 or more of Coxiella, Francisella, Rickettsia or Candidatus Midichloria mitochondrii endosymbionts, indicative of their importance to tick physiology. Genomic and experimental data suggest that endosymbionts promote tick development and reproductive success. Here, we review the limited information currently available on the potential roles endosymbionts play in enhancing tick metabolism and fitness. Future studies that expand on these findings are needed to better understand endosymbionts’ contributions to tick biology. This knowledge could potentially be applied to design novel strategies that target endosymbiont function to control the spread of ticks and pathogens they vector.

Preliminary Study on Artificial versus Animal-Based Feeding Systems for Amblyomma Ticks (Acari: Ixodidae)

Hard ticks pose a threat to animal and human health. Active life stages need to feed on a vertebrate host in order to complete their life cycle. To study processes such as tick-pathogen interactions or drug efficacy and pharmacokinetics, it is necessary to maintain tick colonies under defined laboratory conditions, typically using laboratory animals. The aim of this study was to test a membrane-based artificial feeding system (AFS) applicable for Amblyomma ticks using Amblyomma tonelliae as a biological model. Adult ticks from a laboratory colony were fed in a membrane-based AFS. For comparison, other A. tonelliae adults were fed on calf and rabbit. The proportions of attached (AFS: 76%; calf/rabbit: 100%) and engorged females (AFS: 47.4%; calf/rabbit: 100%) in the AFS were significantly lower compared to animal-based feeding (p = 0.0265). The engorgement weight of in vitro fed ticks (x¯ = 658 mg; SD ± 259.80) did not significantly differ from that of ticks fed on animals (p = 0.3272, respectively 0.0947). The proportion of females that oviposited was 100% for all three feeding methods. However, the incubation period of eggs (x¯ = 54 days; SD ± 7) was longer in the AFS compared to conventional animal-based feeding (p = 0.0014); x¯ = 45 days; SD ± 2 in the rabbit and (p = 0.0144). x¯ = 48 days; SD ± 2 in the calf). Egg cluster hatching (x¯ = 41%; SD ± 44.82) was lower in the AFS than in the other feeding methods (rabbit: x¯ = 74%; SD ± 20; p = 0.0529; calf: x¯ = 81%; SD ± 22; p = 0.0256). Although the attachment, development, and the hatching of AFS ticks were below those from animal-based feeding, the method may be useful in future experiments. Nevertheless, further experiments with a higher number of tick specimens (including immature life stages) and different attractant stimuli are required to confirm the preliminary results of this study and to evaluate the applicability of AFS for Amblyomma ticks as an alternative to animal-based feeding methods.

Changes in the Ixodes ricinus microbiome associated with artificial tick feeding

Artificial tick feeding systems (ATFS) can be used to study tick biology and tick-pathogen interactions. Due to the long feeding duration of hard ticks, antibiotics are commonly added to the in vitro blood meal to prevent the blood from decaying. This may affect the ticks' microbiome, including mutualistic bacteria that play an important role in tick biology. This effect was examined by the consecutive feeding of Ixodes ricinus larvae, nymphs, and adults in vitro with and without the supplementation of gentamicin and in parallel on calves. DNA extracted from unfed females was analyzed by 16S rRNA sequencing. The abundance of Candidatus Midichloria mitochondrii, Rickettsia helvetica and Spiroplasma spp. was measured by qPCR in unfed larvae, nymphs, and adults. Larvae and nymphs fed on calves performed significantly better compared to both in vitro groups. Adults fed on blood supplemented with gentamicin and B vitamins had a higher detachment proportion and weight compared to the group fed with B vitamins but without gentamicin. The detachment proportion and weights of females did not differ significantly between ticks fed on calves and in vitro with gentamicin, but the fecundity was significantly higher in ticks fed on calves. 16S rRNA sequencing showed a higher microbiome species richness in ticks fed on calves compared to ticks fed in vitro. A shift in microbiome composition, with Ca. Midichloria mitochondrii as dominant species in females fed as juveniles on calves and R. helvetica as the most abundant species in females previously fed in vitro was observed. Females fed in vitro without gentamicin showed significant lower loads of Ca. M. mitochondrii compared to females fed in vitro with gentamicin and ticks fed on calves. Spiroplasma spp. were exclusively detected in female ticks fed on cattle by qPCR, but 16S rRNA sequencing results also showed a low abundance in in vitro females exposed to gentamicin. In conclusion, the employed feeding method and gentamicin supplementation affected the ticks' microbiome composition and fecundity. Since these changes may have an impact on tick biology and vector competence, they should be taken into account in studies employing ATFS.

Ixodes ricinus ticks have a functional association with Midichloria mitochondrii

In addition to being vectors of pathogenic bacteria, ticks also harbor intracellular bacteria that associate with ticks over generations, aka symbionts. The biological significance of such bacterial symbiosis has been described in several tick species but its function in Ixodes ricinus is not understood. We have previously shown that I. ricinus ticks are primarily inhabited by a single species of symbiont, Midichloria mitochondrii, an intracellular bacterium that resides and reproduces mainly in the mitochondria of ovaries of fully engorged I. ricinus females. To study the functional integration of M. mitochondrii into the biology of I. ricinus, an M. mitochondrii-depleted model of I. ricinus ticks was sought. Various techniques have been described in the literature to achieve dysbiosed or apo-symbiotic ticks with various degrees of success. To address the lack of a standardized experimental procedure for the production of apo-symbiotic ticks, we present here an approach utilizing the ex vivo membrane blood feeding system. In order to deplete M. mitochondrii from ovaries, we supplemented dietary blood with tetracycline. We noted, however, that the use of tetracycline caused immediate toxicity in ticks, caused by impairment of mitochondrial proteosynthesis. To overcome the tetracycline-mediated off-target effect, we established a protocol that leads to the production of an apo-symbiotic strain of I. ricinus, which can be sustained in subsequent generations. In two generations following tetracycline administration and tetracycline-mediated symbiont reduction, M. mitochondrii was gradually eliminated from the lineage. Larvae hatched from eggs laid by such M. mitochondrii-free females repeatedly performed poorly during blood-feeding, while the nymphs and adults performed similarly to controls. These data indicate that M. mitochondrii represents an integral component of tick ovarian tissue, and when absent, results in the formation of substandard larvae with reduced capacity to blood-feed.

Effects of temperature on cathepsin B, cathepsin D and acid phosphatase during embryo development of the hard tick Haemaphysalis longicornis

The effects of temperature on the expression patterns and enzyme activity of cathepsin B (HlCatB), cathepsin D (HlCatD) and acid phosphatase (HlACP) during the embryo development of Haemaphysalis longicornis (bisexual population) were investigated in this study. Eggs were exposed to 20 °C (low temperature), 26 °C (normal temperature), and 30 °C (high temperature) immediately after laying, and collected on odd days of embryo development to measure HlCatB, HlCatD and HlACP gene expression using quantitative real-time PCR, as well as three enzyme activities using spectrophotometry. Then the associations between mRNA expression levels of three enzymes and their enzyme activities were assessed. Compared with normal temperature, the mRNA expression peaks of HlCatB were higher and appeared later at low and high temperatures and the activity of HlCatB increased on most days of embryonic development at high temperature. As for HlCatD, the expression peak appeared later at low temperature, but earlier at high temperature. The activity peaks of HlCatD were lower and appeared earlier at low and high temperatures. As for HlACP, the expression peak was higher and appeared later at low temperature, whereas it formed no prominent peak at high temperature. The activity peak of HlACP was higher at low temperature, but lower at high temperature. The linear regression analysis showed that activities of three enzymes were associated with their mRNA expression levels (P < 0.05). Three enzymes are involved in the embryo adaptation to temperature stress. Moreover, the mRNA expression level may be another factor affecting its enzyme activity.

What do we know about the microbiome of I. ricinus?

I. ricinus is an obligate hematophagous parasitic arthropod that is responsible for the transmission of a wide range of zoonotic pathogens including spirochetes of the genus Borrelia, Rickettsia spp., C. burnetii, Anaplasma phagocytophilum and Francisella tularensis, which are part the tick´s microbiome. Most of the studies focus on "pathogens" and only very few elucidate the role of "non-pathogenic" symbiotic microorganisms in I. ricinus. While most of the members of the microbiome are leading an intracellular lifestyle, they are able to complement tick´s nutrition and stress response having a great impact on tick´s survival and transmission of pathogens. The composition of the tick´s microbiome is not consistent and can be tied to the environment, tick species, developmental stage, or specific organ or tissue. Ovarian tissue harbors a stable microbiome consisting mainly but not exclusively of endosymbiotic bacteria, while the microbiome of the digestive system is rather unstable, and together with salivary glands, is mostly comprised of pathogens. The most prevalent endosymbionts found in ticks are Rickettsia spp., Ricketsiella spp., Coxiella-like and Francisella-like endosymbionts, Spiroplasma spp. and Candidatus Midichloria spp. Since microorganisms can modify ticks' behavior, such as mobility, feeding or saliva production, which results in increased survival rates, we aimed to elucidate the potential, tight relationship, and interaction between bacteria of the I. ricinus microbiome. Here we show that endosymbionts including Coxiella-like spp., can provide I. ricinus with different types of vitamin B (B2, B6, B7, B9) essential for eukaryotic organisms. Furthermore, we hypothesize that survival of Wolbachia spp., or the bacterial pathogen A. phagocytophilum can be supported by the tick itself since coinfection with symbiotic Spiroplasma ixodetis provides I. ricinus with complete metabolic pathway of folate biosynthesis necessary for DNA synthesis and cell division. Manipulation of tick´s endosymbiotic microbiome could present a perspective way of I. ricinus control and regulation of spread of emerging bacterial pathogens.

Wild Hedgehogs and Their Parasitic Ticks Coinfected with Multiple Tick-Borne Pathogens in Jiangsu Province, Eastern China

The increasing awareness of emerging tickborne pathogens (TBPs) has inspired much research. In the present study, the coinfections of TBPs both in ticks and their wild hedgehog hosts in Jiangsu province, Eastern China were determined by metagenome next-generation sequencing and nested PCR. As a result, Rickettsia japonica (81.1%), novel Rickettsia sp. SFGR-1 (5.1%), Anaplasma bovis (12%), A. platys (6.3%), novel Ehrlichia spp. Ehr-1 (16%) and Ehr-2 (0.6%), E. ewingii-like strain (0.6%), Coxiella burnetii (10.9%), and a novel Coxiella-like endosymbiont (CLE) strain (61.1%) were detected in Haemaphysalis flava ticks. A. bovis (43.8%), Ehrlichia sp. Ehr-1 (83.3%), and C. burnetii (80%) were detected in Erinaceus amurensis hedgehogs. Coinfection rates with various TBPs were 71.5% and 83.3% in ticks and hedgehogs, respectively, both with double-pathogen/endosymbiont coinfection rates over 50%. We found the following. (i) Er. amurensis hedgehogs seem to contribute to the natural cycles of R. japonica, A. bovis, Ehrlichia sp., and C. burnetii and may be reservoirs of them except for R. japonica, and A. bovis is proved to infect hedgehogs for the first time. (ii) H. flava is proved to harbor various TBPs as a reservoir host, including CLE identified for the first time, which could inhibit coinfection of C. burnetii while promoting that of Rickettsia spp. in H. flava. (iii) Four novel TBP species were identified. This study provides useful epidemiological information crucial for assessing the potential infection risks to humans, thus benefiting the development of strategies to prevent and control tick-borne diseases. IMPORTANCE In the present study, we found the following. (i) Er. amurensis hedgehogs seem to contribute to the natural cycles of R. japonica, A. bovis, Ehrlichia sp., and C. burnetii and may be reservoirs of them except for R. japonica, and A. bovis is proved to infect hedgehogs for the first time. (ii) H. flava is proved to harbor various tickborne pathogens (TBPs) as a reservoir host, including Coxiella-like endosymbiont (CLE) identified for the first time, which could inhibit coinfection of C. burnetii while promoting that of Rickettsia spp. in H. flava. (iii) Four novel TBP species were identified. This study provides useful epidemiological information on TBPs harbored and transmitted by ticks and their hosts, for assessing the potential infection risks to humans, thus benefiting the developing strategies for tick-borne diseases prevention and control.

Molecular Detection of Tick-Borne Bacteria from Amblyomma (Acari: Ixodidae) Ticks Collected from Reptiles in South Africa

Reptiles are hosts for various tick species and tick-associated organisms, many of which are zoonotic. However, little is known about the presence and diversity of tick-borne bacteria infecting reptiles and their ticks in South Africa. Amblyomma ticks (n = 253) collected from reptiles were screened for the presence of Coxiella, Anaplasma, Rickettsia, and Borrelia species by amplification, sequencing and phylogenetic analysis of the 16S rRNA, 23S rRNA, gltA, OmpA, and Flagellin genes, respectively. This study recorded the presence of reptile associated Borrelia species and Coxiella-like endosymbiont in South Africa for the first time. Furthermore, a spotted fever group Rickettsia species was observed in 7 Amblyomma marmoreum and 14 Amblyomma sylvaticum from tortoises of genera Kinixys and Chersina. Francisella-like endosymbiont was observed from 2 Amblyomma latum collected from the Mozambique spitting cobra, Naja mossambica. Coxiella burnetii and Anaplasma spp., were not detected from the current samples. Although the direct evidence that reptiles can act as reservoir hosts remains to be determined, observations from this study provide indications that reptilian ticks may play a role in the transmission of pathogenic bacteria to homothermic animals. Furthermore, the absence of Anaplasma spp., and C. burnetii does not mean that these pathogens should be completely neglected.

The microbiota changes of the brown dog tick, Rhipicephalus sanguineus under starvation stress

Rhipicephalus sanguineus, the brown dog tick, is the most widespread tick in the world and a predominant vector of multiple pathogens affecting wild and domestic animals. There is an increasing interest in understanding the role of tick microbiome in pathogen acquisition and transmission as well as in environment–vector interfaces. Several studies suggested that the tick microbial communities are under the influence of several factors including the tick species, dietary bloodmeal, and physiological stress. Compared with insects, very little of the microbial community is known to contribute to the nutrition of the host. Therefore, it is of significance to elucidate the regulation of the microbial community of Rh. Sanguineus under starvation stress. Starvation stress was induced in wild-type adults (1 month, 2 months, 4 months, 6 months) and the microbial composition and diversity were analyzed before and after blood feeding. After the evaluation, it was found that the microbial community composition of Rh. sanguineus changed significantly with starvation stress. The dominant symbiotic bacteria Coxiella spp. of Rh. sanguineus gradually decreased with the prolongation of starvation stress. We also demonstrated that the starvation tolerance of Rh. sanguineus was as long as 6 months. Next, Coxiella-like endosymbionts were quantitatively analyzed by fluorescence quantitative PCR. We found a pronounced tissue tropism in the Malpighian tubule and female gonad, and less in the midgut and salivary gland organs. Finally, the blood-fed nymphs were injected with ofloxacin within 24 h. The nymphs were allowed to develop into adults. It was found that the adult blood-sucking rate, adult weight after blood meal, fecundity (egg hatching rate), and feeding period of the newly hatched larvae were all affected to varying degrees, indicating that the removal of most symbiotic bacteria had an irreversible effect on it.

Growth dynamics and tissue localization of a Coxiella-like endosymbiont in the tick Haemaphysalis longicornis

A Coxiella-like endosymbiont (Coxiella-LE hereinafter) stably infects and influences Haemaphysalis longicornis development, indicating a mutualistic relationship of Coxiella-LE and ticks. To further elucidate the patterns of growth dynamics and tissue localization of Coxiella-LE in H. longicornis, 16S rRNA high-throughput sequencing, quantitative PCR (qPCR), and fluorescence in situ hybridization (FISH) were used in this study. The density of Coxiella-LE varied among different tick life stages, and fed female ticks had the highest density, followed by unfed female and unfed larval ticks. In the four organs that were dissected from fed female ticks, the ovary carried the highest density of Coxiella-LE, which was significantly different from salivary glands, midgut and Malpighian tubules. The high abundance of Coxiella-LE in fed female ticks and in the ovaries of fed female ticks in the bacterial microbiota analyses further confirmed that Coxiella-LE rapidly proliferates in the ovary after blood feeding. The ovaries continued to develop after engorgement and oviposition began on day 5, with a significant decrease in the density of Coxiella-LE in the ovaries occurring on day 7. FISH results indicated that Coxiella-LE is mainly colonized in the cytoplasm of the oocyte and proliferates with oogenesis. Coxiella-LE was expelled from the body with the mature oocyte, ensuring its vertical transmission. In the Malpighian tubules at different days after engorgement, the white flocculent materials were increasing, and the density of Coxiella-LE raised significantly on day 7. Unlike the localization pattern in the ovary, Coxiella-LE was initially distributed in a mass and continually increased during the development of Malpighian tubules until it filled the Malpighian tubules. These findings provide new insights on the growth dynamics and tissue localization of Coxiella-LE in ticks and are useful for further investigation on the interactions of symbiont and ticks .

Coxiella Endosymbiont of Rhipicephalus microplus Modulates Tick Physiology With a Major Impact in Blood Feeding Capacity

In the past decade, metagenomics studies exploring tick microbiota have revealed widespread interactions between bacteria and arthropods, including symbiotic interactions. Functional studies showed that obligate endosymbionts contribute to tick biology, affecting reproductive fitness and molting. Understanding the molecular basis of the interaction between ticks and their mutualist endosymbionts may help to develop control methods based on microbiome manipulation. Previously, we showed that Rhipicephalus microplus larvae with reduced levels of Coxiella endosymbiont of R. microplus (CERM) were arrested at the metanymph life stage (partially engorged nymph) and did not molt into adults. In this study, we performed a transcriptomic differential analysis of the R. microplus metanymph in the presence and absence of its mutualist endosymbiont. The lack of CERM resulted in an altered expression profile of transcripts from several functional categories. Gene products such as DA-P36, protease inhibitors, metalloproteases, and evasins, which are involved in blood feeding capacity, were underexpressed in CERM-free metanymphs. Disregulation in genes related to extracellular matrix remodeling was also observed in the absence of the symbiont. Taken together, the observed alterations in gene expression may explain the blockage of development at the metanymph stage and reveal a novel physiological aspect of the symbiont-tick-vertebrate host interaction.

Bacterial microbiota analysis demonstrates that ticks can acquire bacteria from habitat and host blood meal

Ticks have a diversity of habitats and host blood meals. Whether and how factors such as tick developmental stages, habitats and host blood meals affect tick bacterial microbiota is poorly elucidated. In the present study, we investigated the bacterial microbiotas of the hard tick Haemaphysalis longicornis, their blood meals and habitats using 16S rRNA gene high-throughput sequencing. The bacterial richness and diversity in ticks varied depending on the tick developmental stage and feeding status. Results showed that fed ticks present a higher bacterial richness suggesting that ticks may acquire bacteria from blood meals. The significant overlap of the bacteria of fed ticks and the host blood also supports this possibility. Another possibility is that blood meals can stimulate the proliferation of certain bacteria. However, most shared bacteria cannot transmit throughout the tick life cycle, as they were not present in tick eggs. The most shared bacteria between ticks and habitats are members of the genera Staphylococcus, Pseudomonas, Enterobacter, Acinetobacter and Stenotrophomonas, suggesting that these environmental bacteria cannot be completely washed away and can be acquired by ticks. The predominant proportion of Coxiella in fed females further demonstrates that this genus is involved in H. longicornis physiology, such as feeding activity and nutritional provision. These findings further reveal that the bacterial composition of ticks is influenced by a variety of factors and will help in subsequent studies of the function of these bacteria.

Phylogenetic Studies of Coxiella-Like Bacteria and Spotted Fever Group Rickettsiae in Ticks Collected From Vegetation in Chaiyaphum Province, Thailand

Ticks can transmit a wide variety of pathogens, including bacteria. Here, we report the detection of tick-associated bacteria in Chaiyaphum Province, northeastern Thailand. There have been few reports of tick-borne bacterial pathogens in the study areas, which are evergreen forests dominated by plateaus at elevations of approximately 1,000 m. In total, 94 ticks were collected from vegetation. They were screened for the presence of Coxiella, Francisella, Rickettsia, and Borrelia bacteria using PCR assays. In this study, we found ticks from two genera, Haemaphysalis and Amblyomma, that were positive for Coxiella-like bacteria (CLB) and Rickettsia. Francisella and Borrelia spp. were not detected in these two tick genera. The results revealed the evolutionary relationships of CLB in Amblyomma testudinarium, Haemaphysalis lagrangei, and Haemaphysalis obesa ticks using the 16S rRNA and rpoB markers, which clustered together with known isolates of ticks from the same genera. In contrast, the groEL marker showed different results. On the basis of the groEL phylogenetic analysis and BLAST results, three groups of CLB were found: (1) CLB from A. testudinarium grouped as a sister clade to CLB from Ixodes ricinus; (2) CLB from Haemaphysalis lagrangei was distantly related to CLB from Haemaphysalis wellingtoni; and (3) CLB from A. testudinarium grouped as sister clade to CLB from Amblyomma from French Guiana and Brazil. For Rickettsia studies, phylogenetic trees of the gltA, ompB, and sca4 genes revealed two groups of Spotted Fever Group (SFG) Rickettsiae: (1) SFG Rickettsiae that formed a sister clade with Rickettsia tamurae AT-1 (belong to the Rickettsia helvetica subgroup) in A. testudinarium and (2) SFG Rickettsiae that formed a distantly related group to Rickettsia rhipicephali 3-7-female6-CWPP (belong to the Rickettsia massiliae subgroup) in A. testudinarium. This study expanded our knowledge of the diversity of tick-borne Coxiella and Rickettsia bacteria. The pathogenic roles of these bacteria also need to be investigated further.

Ecological Contacts and Host Specificity Promote Replacement of Nutritional Endosymbionts in Ticks

Symbiosis with vitamin-provisioning microbes is essential for the nutrition of animals with some specialized feeding habits. While coevolution favors the interdependence between symbiotic partners, their associations are not necessarily stable: Recently acquired symbionts can replace ancestral symbionts. In this study, we demonstrate successful replacement by Francisella-like endosymbionts (-LE), a group of B-vitamin-provisioning endosymbionts, across tick communities driven by horizontal transfers. Using a broad collection of Francisella-LE-infected tick species, we determined the diversity of Francisella-LE haplotypes through a multi-locus strain typing approach and further characterized their phylogenetic relationships and their association with biological traits of their tick hosts. The patterns observed showed that Francisella-LE commonly transfer through similar ecological networks and geographic distributions shared among different tick species and, in certain cases, through preferential shuffling across congeneric tick species. Altogether, these findings reveal the importance of geographic, ecological, and phylogenetic proximity in shaping the replacement pattern in which new nutritional symbioses are initiated.

Current debates and advances in tick microbiome research

The main importance of ticks resides in their ability to harbor pathogens that can be transmitted to terrestrial vertebrates including humans. Recently, studies have focused on the taxonomic and functional composition of the tick microbiome, its microbial diversity and variation under different factors including tick species, sex, and environment among others. Of special interest are the interactions between the tick, the microbiome and pathogens since tick microbiome can influence pathogen colonization within the tick vector, and potentially, transmission to the vertebrate host. In this review, we tackled a synthesis on the growing field of tick microbiomes. We focus on the current state of tick microbiome research, addressing controversial and hotly debated topics and advances in the precise manipulation of tick microbiome. Furthermore, we discuss the innovative anti-tick microbiota vaccines as a possible tool for microbiome modulation and thus, control of tick-borne diseases. Deciphering tick-microbiome pathogen interactions can spur new strategies to control tick-borne diseases via modulation of tick microbiome.

•

Whether the diversity observed in tick microbiomes concerns the biology or the methodology remains an open question.

•

Tick immunity must play a major role in selecting ‘who stays and who leaves’ the microbiome.

•

Anti-tick microbiota vaccines can target specific bacteria and subsequently modulate tick microbiome.

Illuminating the bacterial microbiome of Australian ticks with 16S and Rickettsia-specific next-generation sequencing

Next-generation sequencing (NGS) studies show that mosquito and tick microbiomes influence the transmission of pathogens, opening new avenues for vector-borne pathogen control. Recent microbiological studies of Australian ticks highlight fundamental knowledge gaps of tick-borne agents. This investigation explored the composition, diversity and prevalence of bacteria in Australian ticks (n = 655) from companion animals (dogs, cats and horses). Bacterial 16S NGS was used to identify most bacterial taxa and a Rickettsia-specific NGS assay was developed to identify Rickettsia species that were indistinguishable at the V1-2 regions of 16S. Sanger sequencing of near full-length 16S was used to confirm whether species detected by 16S NGS were novel. The haemotropic bacterial pathogens Anaplasma platys, Bartonella clarridgeiae, “Candidatus Mycoplasma haematoparvum” and Coxiella burnetii were identified in Rhipicephalus sanguineus (s.l.) from Queensland (QLD), Western Australia, the Northern Territory (NT), and South Australia, Ixodes holocyclus from QLD, Rh. sanguineus (s.l.) from the NT, and I. holocyclus from QLD, respectively. Analysis of the control data showed that cross-talk compromises the detection of rare species as filtering thresholds for less abundant sequences had to be applied to mitigate false positives. A comparison of the taxonomic assignments made with 16S sequence databases revealed inconsistencies. The Rickettsia-specific citrate synthase gene NGS assay enabled the identification of Rickettsia co-infections with potentially novel species and genotypes most similar (97.9–99.1%) to Rickettsia raoultii and Rickettsia gravesii. “Candidatus Rickettsia jingxinensis” was identified for the first time in Australia. Phylogenetic analysis of near full-length 16S sequences confirmed a novel Coxiellaceae genus and species, two novel Francisella species, and two novel Francisella genotypes. Cross-talk raises concerns for the MiSeq platform as a diagnostic tool for clinical samples. This study provides recommendations for adjustments to Illuminaʼs 16S metagenomic sequencing protocol that help track and reduce cross-talk from cross-contamination during library preparation. The inconsistencies in taxonomic assignment emphasise the need for curated and quality-checked sequence databases.

•

Bacterial pathogens identified in ticks from companion animals with 16S NGS.

•

Sanger sequencing confirmed novel Coxiellaceae gen. sp. and Francisella.

•

“Candidatus Rickettsia jingxinensis” was identified with Rickettsia-specific NGS.

•

Comparison of taxonomic assignments in 16S sequence databases revealed errors.

•

Modifications to the 16S metagenomic library protocol (Illumina) are provided.

Comparative Proteomics of Coxiella like Endosymbionts (CLEs) in the Symbiotic Organs of Rhipicephalus sanguineus Ticks

Maternally transmitted obligatory endosymbionts are found in the female gonads as well as in somatic tissue and are expected to provide missing metabolite to their hosts. These deficiencies are presumably complemented through specific symbiotic microorganisms such as Coxiella-like endosymbionts (CLEs) of Rhipicephalus ticks. CLEs are localized in specialized host tissue cells within the Malpighian tubules (Mt) and the ovaries (Ov) from which they are maternally transmitted to developing oocytes. These two organs differ in function and cell types, but the role of CLEs in these tissues is unknown. To probe possible functions of CLEs, comparative proteomics was performed between Mt and Ov of R. sanguineus ticks. Altogether, a total of 580 and 614 CLE proteins were identified in Mt and Ov, respectively. Of these, 276 CLE proteins were more abundant in Mt, of which 12 were significantly differentially abundant. In Ov, 290 CLE proteins were more abundant, of which 16 were significantly differentially abundant. Gene Ontology analysis revealed that most of the proteins enriched in Mt are related to cellular metabolic functions and stress responses, whereas in Ov, the majority were related to cell proliferation suggesting CLEs function differentially and interdependently with host requirements specific to each organ. The results suggest Mt CLEs provide essential nutrients to its host and Ov CLEs promote proliferation and vertical transmission to tick progeny. IMPORTANCE Here we compare the Coxiella-like endosymbionts (CLEs) proteomes from Malpighian tubule (Mt) and the ovaries (Ov) of the brown dog tick Rhipicephalus sanguineus. Our results support the hypothesis that CLEs function interdependently with host requirements in each of the organs. The different functional specificity of CLE in the same host suggest that metabolic capabilities evolved according to the constrains imposed by the specific organ function and requirements. Our findings provide specific CLE protein targets that can be useful for future studies of CLE biology with a focus on tick population control.

Symbiont-regulated serotonin biosynthesis modulates tick feeding activity

Ticks are obligate hematophagous arthropods. Blood feeding ensures that ticks obtain nutrients essential for their survival, development, and reproduction while providing routes for pathogen transmission. However, the effectors that determine tick feeding activities remain poorly understood. Here, we demonstrate that reduced abundance of the symbiont Coxiella (CHI) in Haemaphysalis longicornis decreases blood intake. Providing tetracycline-treated ticks with the CHI-derived tryptophan precursor chorismate, tryptophan, or 5-hydroxytryptamine (5-HT; serotonin) restores the feeding defect. Mechanistically, CHI-derived chorismate increases tick 5-HT biosynthesis by stimulating the expression of aromatic amino acid decarboxylase (AAAD), which catalyzes the decarboxylation of 5-hydroxytryptophan (5-HTP) to 5-HT. The increased level of 5-HT in the synganglion and midgut promotes tick feeding. Inhibition of CHI chorismate biosynthesis by treating the colonized tick with the herbicide glyphosate suppresses blood-feeding behavior. Taken together, our results demonstrate an important function of the endosymbiont Coxiella in the regulation of tick 5-HT biosynthesis and feeding.

Approaches to Integrated Parasite Management (IPM) for Theileria orientalis with an Emphasis on Immunity

Integrated parasite management (IPM) for pests, pathogens and parasites involves reducing or breaking transmission to reduce the impact of infection or infestation. For Theileria orientalis, the critical impact of infection is the first wave of parasitaemia from the virulent genotypes, Ikeda and Chitose, associated with the sequelae from the development of anaemia. Therefore, current control measures for T. orientalis advocate excluding the movement of naïve stock from non-endemic regions into infected areas and controlling the tick Haemaphysalislongicornis, the final host. In Australia, treatment of established infection is limited to supportive therapy. To update and expand these options, this review examines progress towards prevention and therapy for T. orientalis, which are key elements for inclusion in IPM measures to control this parasite.

Borrelia afzelii Infection in the Rodent Host Has Dramatic Effects on the Bacterial Microbiome of Ixodes ricinus Ticks

The microbiome of blood-sucking arthropods can shape their competence to acquire and maintain infections with vector-borne pathogens. We used a controlled study to investigate the interactions between Borrelia afzelii, which causes Lyme borreliosis in Europe, and the bacterial microbiome of Ixodes ricinus, its primary tick vector. We applied a surface sterilization treatment to I. ricinus eggs to produce dysbiosed tick larvae that had a low bacterial abundance and a changed bacterial microbiome compared to those of the control larvae. Dysbiosed and control larvae fed on B. afzelii-infected mice and uninfected control mice, and the engorged larvae were left to molt into nymphs. The nymphs were tested for B. afzelii infection, and their bacterial microbiome underwent 16S rRNA amplicon sequencing. Surprisingly, larval dysbiosis had no effect on the vector competence of I. ricinus for B. afzelii, as the nymphal infection prevalence and the nymphal spirochete load were the same between the dysbiosed group and the control group. The strong effect of egg surface sterilization on the tick bacterial microbiome largely disappeared once the larvae molted into nymphs. The most important determinant of the bacterial microbiome of I. ricinus nymphs was the B. afzelii infection status of the mouse on which the nymphs had fed as larvae. Nymphs that had taken their larval blood meal from an infected mouse had a less abundant but more diverse bacterial microbiome than the control nymphs. Our study demonstrates that vector-borne infections in the vertebrate host shape the microbiome of the arthropod vector. IMPORTANCE Many blood-sucking arthropods transmit pathogens that cause infectious disease. For example, Ixodes ricinus ticks transmit the bacterium Borrelia afzelii, which causes Lyme disease in humans. Ticks also have a microbiome, which can influence their ability to acquire and transmit tick-borne pathogens such as B. afzelii. We sterilized I. ricinus eggs with bleach, and the tick larvae that hatched from these eggs had a dramatically reduced and changed bacterial microbiome compared to that of control larvae. These larvae fed on B. afzelii-infected mice, and the resultant nymphs were tested for B. afzelii and for their bacterial microbiome. We found that our manipulation of the bacterial microbiome had no effect on the ability of the tick larvae to acquire and maintain populations of B. afzelii. In contrast, we found that B. afzelii infection had dramatic effects on the bacterial microbiome of I. ricinus nymphs. Our study demonstrates that infections in the vertebrate host can shape the tick microbiome.

Anti-Microbiota Vaccines Modulate the Tick Microbiome in a Taxon-Specific Manner

The lack of tools for the precise manipulation of the tick microbiome is currently a major limitation to achieve mechanistic insights into the tick microbiome. Anti-tick microbiota vaccines targeting keystone bacteria of the tick microbiota alter tick feeding, but their impact on the taxonomic and functional profiles of the tick microbiome has not been tested. In this study, we immunized a vertebrate host model (Mus musculus) with live bacteria vaccines targeting keystone (i.e., Escherichia-Shigella) or non-keystone (i.e., Leuconostoc) taxa of tick microbiota and tested the impact of bacterial-specific antibodies (Abs) on the structure and function of tick microbiota. We also investigated the effect of these anti-microbiota vaccines on mice gut microbiota composition. Our results showed that the tick microbiota of ticks fed on Escherichia coli-immunized mice had reduced Escherichia-Shigella abundance and lower species diversity compared to ticks fed on control mice immunized with a mock vaccine. Immunization against keystone bacteria restructured the hierarchy of nodes in co-occurrence networks and reduced the resistance of the bacterial network to taxa removal. High levels of E. coli-specific IgM and IgG were negatively correlated with the abundance of Escherichia-Shigella in tick microbiota. These effects were not observed when Leuconostoc was targeted with vaccination against Leuconostoc mesenteroides. Prediction of functional pathways in the tick microbiome using PICRUSt2 revealed that E. coli vaccination reduced the abundance of lysine degradation pathway in tick microbiome, a result validated by qPCR. In contrast, the gut microbiome of immunized mice showed no significant alterations in the diversity, composition and abundance of bacterial taxa. Our results demonstrated that anti-tick microbiota vaccines are a safe, specific and an easy-to-use tool for manipulation of vector microbiome. These results guide interventions for the control of tick infestations and pathogen infection/transmission.

Infection with Borrelia afzelii and manipulation of the egg surface microbiota have no effect on the fitness of immature Ixodes ricinus ticks

Arthropod vectors carry vector-borne pathogens that cause infectious disease in vertebrate hosts, and arthropod-associated microbiota, which consists of non-pathogenic microorganisms. Vector-borne pathogens and the microbiota can both influence the fitness of their arthropod vectors, and hence the epidemiology of vector-borne diseases. The bacterium Borrelia afzelii, which causes Lyme borreliosis in Europe, is transmitted among vertebrate reservoir hosts by Ixodes ricinus ticks, which also harbour a diverse microbiota of non-pathogenic bacteria. The purpose of this controlled study was to test whether B. afzelii and the tick-associated microbiota influence the fitness of I. ricinus. Eggs obtained from field-collected adult female ticks were surface sterilized (with bleach and ethanol), which reduced the abundance of the bacterial microbiota in the hatched I. ricinus larvae by 28-fold compared to larvae that hatched from control eggs washed with water. The dysbiosed and control larvae were subsequently fed on B. afzelii-infected or uninfected control mice, and the engorged larvae were left to moult into nymphs under laboratory conditions. I. ricinus larvae that fed on B. afzelii-infected mice had a significantly faster larva-to-nymph moulting time compared to larvae that fed on uninfected control mice, but the effect was small (2.4% reduction) and unlikely to be biologically significant. We found no evidence that B. afzelii infection or reduction of the larval microbiota influenced the four other life history traits of the immature I. ricinus ticks, which included engorged larval weight, unfed nymphal weight, larva-to-nymph moulting success, and immature tick survival. A retrospective power analysis found that our sampling effort had sufficient power (> 80%) to detect small effects (differences of 5% to 10%) of our treatments. Under the environmental conditions of this study, we conclude that B. afzelii and the egg surface microbiota had no meaningful effects on tick fitness and hence on the R₀ of Lyme borreliosis.

Coxiella burnetii and Related Tick Endosymbionts Evolved from Pathogenic Ancestors

Both symbiotic and pathogenic bacteria in the family Coxiellaceae cause morbidity and mortality in humans and animals. For instance, Coxiella-like endosymbionts (CLEs) improve the reproductive success of ticks—a major disease vector, while Coxiella burnetii causes human Q fever, and uncharacterized coxiellae infect both animals and humans. To better understand the evolution of pathogenesis and symbiosis in this group of intracellular bacteria, we sequenced the genome of a CLE present in the soft tick Ornithodoros amblus (CLEOA) and compared it to the genomes of other bacteria in the order Legionellales. Our analyses confirmed that CLEOA is more closely related to C. burnetii, the human pathogen, than to CLEs in hard ticks, and showed that most clades of CLEs contain both endosymbionts and pathogens, indicating that several CLE lineages have evolved independently from pathogenic Coxiella. We also determined that the last common ancestorof CLEOA and C. burnetii was equipped to infect macrophages and that even though horizontal gene transfer (HGT) contributed significantly to the evolution of C. burnetii, most acquisition events occurred primarily in ancestors predating the CLEOA–C. burnetii divergence. These discoveries clarify the evolution of C. burnetii, which previously was assumed to have emerged when an avirulent tick endosymbiont recently gained virulence factors via HGT. Finally, we identified several metabolic pathways, including heme biosynthesis, that are likely critical to the intracellular growth of the human pathogen but not the tick symbiont, and show that the use of heme analog is a promising approach to controlling C. burnetii infections.

The Prevalence of Coxiella burnetii in Hard Ticks in Europe and Their Role in Q Fever Transmission Revisited-A Systematic Review

The zoonosis Q fever is caused by the obligate intracellular bacterium Coxiella burnetii. Besides the main transmission route via inhalation of contaminated aerosols, ticks are discussed as vectors since the first isolation of the pathogen from a Dermacentor andersonii tick. The rare detection of C. burnetii in ticks and the difficult differentiation of C. burnetii from Coxiella-like endosymbionts (CLEs) are questioning the relevance of ticks in the epidemiology of Q fever. In this review, literature databases were systematically searched for recent prevalence studies concerning C. burnetii in ticks in Europe and experimental studies evaluating the vector competence of tick species. A total of 72 prevalence studies were included and evaluated regarding DNA detection methods and collection methods, country, and tested tick species. Specimens of more than 25 different tick species were collected in 23 European countries. Overall, an average prevalence of 4.8% was determined. However, in half of the studies, no Coxiella-DNA was detected. In Southern European countries, a significantly higher prevalence was observed, possibly related to the abundance of different tick species here, namely Hyalomma spp. and Rhipicephalus spp. In comparison, a similar proportion of studies used ticks sampled by flagging and dragging or tick collection from animals, under 30% of the total tick samples derived from the latter. There was no significant difference in the various target genes used for the molecular test. In most of the studies, no distinction was made between C. burnetii and CLEs. The application of specific detection methods and the confirmation of positive results are crucial to determine the role of ticks in Q fever transmission. Only two studies were available, which assessed the vector competence of ticks for C. burnetii in the last 20 years, demonstrating the need for further research.

Artificial Feeding of All Consecutive Life Stages of Ixodes ricinus

The hard tick Ixodes ricinus is an obligate hematophagous arthropod and the main vector for several zoonotic diseases. The life cycle of this three-host tick species was completed for the first time in vitro by feeding all consecutive life stages using an artificial tick feeding system (ATFS) on heparinized bovine blood supplemented with glucose, adenosine triphosphate, and gentamicin. Relevant physiological parameters were compared to ticks fed on cattle (in vivo). All in vitro feedings lasted significantly longer and the mean engorgement weight of F₀ adults and F₁ larvae and nymphs was significantly lower compared to ticks fed in vivo. The proportions of engorged ticks were significantly lower for in vitro fed adults and nymphs as well, but higher for in vitro fed larvae. F₁-females fed on blood supplemented with vitamin B had a higher detachment proportion and engorgement weight compared to F₁-females fed on blood without vitamin B, suggesting that vitamin B supplementation is essential in the artificial feeding of I. ricinus ticks previously exposed to gentamicin.

Symbiont dynamics during the blood meal of Ixodes ricinus nymphs differ according to their sex

Ticks harbour rich and diverse microbiota and, among the microorganisms associated with them, endosymbionts are the subject of a growing interest due to their crucial role in the biology of their arthropod host. Midichloria mitochondrii is the main endosymbiont of the European tick Ixodes ricinus and is found in abundance in all I. ricinus females, while at a much lower density in males, where it is even absent in 56 % of the individuals. This endosymbiont is also known to increase in numbers after the blood meal of larvae, nymphs or females. Because of this difference in the prevalence of M. mitochondrii between the two sexes, surveying the density of these bacteria in nymphs that will become either females or males could help to understand the behaviour of Midichloria in its arthropod host. To this aim, we have set up an experimental design by building 3 groups of unfed nymphs based on their scutum and hypostome lengths. After engorgement, weighing and moulting of a subset of the nymphs, a significant difference in sex-ratio among the 3 groups was observed. In parallel, Midichloria load in individual nymphs was quantified by qPCR both before and after engorgement. No difference in either body mass or Midichloria load was observed at the unfed stage, but following engorgement, both features were significantly different between each size group. Our results demonstrate that symbiont dynamics during nymphal engorgement is different between the two sexes, resulting in a significantly higher Midichloria load in nymphs that will become females. The consequences of those findings on our understanding of the interplay between the endosymbiont and its arthropod host are discussed.

Multi-country investigation of the diversity and associated microorganisms isolated from tick species from domestic animals, wildlife and vegetation in selected african countries

In many areas of Africa, recent studies highlighted the great impact of ticks on animal and human health throughout the continent. On the other hand, very limited information on the bacterial endosymbionts of the African ticks and their pattern of co-infections with other bacteria are found in literature, notwithstanding their pivotal role in tick survival and vector efficiency. Thus, we investigated the distribution of selected pathogenic and symbiotic bacteria in hard ticks collected from wild, domestic animals and from vegetation in various ecological zones in Africa and their co-occurrence in the same tick host. Overall, 339 hard ticks were morphologically identified as belonging to the genera Amblyomma, Dermacentor, Hyalomma, Haemaphysalis, Ixodes and Rhipicephalus. Molecular screening provided information on pathogens circulation in Africa, detecting spotted fever group rickettsiae, Anaplasma spp., Ehrlichia ruminantium, Borrelia garinii, Babesia spp., Theileria spp. and Coxiella burnetii. Furthermore, our work provides insights on the African scenario of tick-symbiont associations, revealing the presence of Coxiella, Francisella and Midichloria across multiple tick populations. Coxiella endosymbionts were the most prevalent microorganisms, and that with the broadest spectrum of hosts, being detected in 16 tick species. Francisella was highly prevalent among the Hyalomma species tested and correlated negatively with the presence of Coxiella, showing a potential competitive interaction. Interestingly, we detected a positive association of Francisella with Rickettsia in specimens of Hy. rufipes, suggesting a synergistic interaction between them. Finally, Midichloria was the most prevalent symbiont in Rhipicephalus sanguineus sensu lato from Egypt.

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.

Poor Unstable Midgut Microbiome of Hard Ticks Contrasts With Abundant and Stable Monospecific Microbiome in Ovaries

Culture-independent metagenomic methodologies have enabled detection and identification of microorganisms in various biological systems and often revealed complex and unknown microbiomes. In many organisms, the microbiome outnumbers the host cells and greatly affects the host biology and fitness. Ticks are hematophagous ectoparasites with a wide host range. They vector a number of human and animal pathogens and also directly cause major economic losses in livestock. Although several reports on a tick midgut microbiota show a diverse bacterial community, in most cases the size of the bacterial population has not been determined. In this study, the microbiome was quantified in the midgut and ovaries of the ticks Ixodes ricinus and Rhipicephalus microplus before, during, and after blood feeding. Although the size of bacterial community in the midgut fluctuated with blood feeding, it was overall extremely low in comparison to that of other hematophagous arthropods. In addition, the tick ovarian microbiome of both tick species exceeded the midgut 16S rDNA copy numbers by several orders of magnitude. This indicates that the ratio of a tick midgut/ovary microbiome represents an exception to the general biology of other metazoans. In addition to the very low abundance, the tick midgut diversity in I. ricinus was variable and that is in contrast to that found in the tick ovary. The ovary of I. ricinus had a very low bacterial diversity and a very high and stable bacterial abundance with the dominant endosymbiont, Midichloria sp. The elucidation of this aspect of tick biology highlights a unique tissue-specific microbial-invertebrate host interaction.

Coxiella-Like Endosymbiont of Rhipicephalus sanguineus Is Required for Physiological Processes During Ontogeny

Obligatory hematophagous arthropods such as lice, bugs, flies, and ticks harbor bacterial endosymbionts that are expected to complement missing essential nutrients in their diet. Genomic and some experimental evidence support this expectation. Hard ticks (Acari: Ixodidae) are associated with several lineages of bacterial symbionts, and very few were experimentally shown to be essential to some aspects of tick's fitness. In order to pinpoint the nature of interactions between hard ticks and their symbionts, we tested the effect of massive elimination of Coxiella-like endosymbionts (CLE) by antibiotics on the development and fitness of the brown dog tick (Rhipicephalus sanguineus). Administration of ofloxacin to engorged (blood fed) nymphs resulted in significant and acute reduction of their CLE loads - an effect that also persisted in subsequent life stages (aposymbiotic ticks). As a result, the post-feeding development of aposymbiotic female (but not male) nymphs was delayed. Additionally, aposymbiotic adult females needed a significantly prolonged feeding period in order to replete (detach from host), and had reduced engorgement weight and a lower capacity to produce eggs. Consequently, their fecundity and fertility were significantly reduced. Eggs produced by aposymbiotic females were free of CLE, and the resulting aposymbiotic larvae were unable to feed successfully. Our findings demonstrate that the observed fitness effects are due to CLE reduction and not due to antibiotic administration. Additionally, we suggest that the contribution of CLE is not mandatory for oocyte development and embryogenesis, but is required during feeding in females, when blood meal processing and tissue buildup are taking place. Presumably, under these extreme physiological demands, CLE contribute to R. sanguineus through supplementing essential micro- and macronutrients. Further nutrient complementary studies are required to support this hypothesis.

Comparison of closely related, uncultivated Coxiella tick endosymbiont population genomes reveals clues about the mechanisms of symbiosis

Understanding the symbiotic interaction between Coxiella-like endosymbionts (CLE) and their tick hosts is challenging due to lack of isolates and difficulties in tick functional assays. Here we sequenced the metagenome of a CLE population from wild Rhipicephalus sanguineus ticks (CRs) and compared it to the previously published genome of its close relative, CLE of R. turanicus (CRt). The tick hosts are closely related sympatric species, and their two endosymbiont genomes are highly similar with only minor differences in gene content. Both genomes encode numerous pseudogenes, consistent with an ongoing genome reduction process. In silico flux balance metabolic analysis (FBA) revealed the excess production of L-proline for both genomes, indicating a possible proline transport from Coxiella to the tick. Additionally, both CR genomes encode multiple copies of the proline/betaine transporter, proP gene. Modelling additional Coxiellaceae members including other tick CLE, did not identify proline as an excreted metabolite. Although both CRs and CRt genomes encode intact B vitamin synthesis pathway genes, which are presumed to underlay the mechanism of CLE-tick symbiosis, the FBA analysis indicated no changes for their products. Therefore, this study provides new testable hypotheses for the symbiosis mechanism and a better understanding of CLE genome evolution and diversity.

The bacterial microbiome of field-collected Dermacentor marginatus and Dermacentor reticulatus from Slovakia

Background

The important roles of microbial flora in tick biology and ecology have received much attention. Dermacentor marginatus and Dermacentor reticulatus are known vectors of various pathogens across Europe, including Slovakia. However, their bacterial microbiomes are poorly explored.

Methods

In this study, bacterial microbiomes of field-collected D. marginatus and D. reticulatus from Slovakia were characterized using 16S rRNA high-throughput sequencing.

Results

Different analyses demonstrated that the D. marginatus and D. reticulatus microbiomes differ in their diversity and taxonomic structures. Furthermore, species- and sex-specific bacteria were detected in the two species. A possible bacterial pathogen “Candidatus Rhabdochlamydia sp.” was detected from D. marginatus males. Among the observed bacteria, Rickettsia showed high abundance in the two species. Several maternally inherited bacteria such as Coxiella, Arsenophonus, Spiroplasma, Francisella and Rickettsiella, were abundant, and their relative abundance varied depending on tick species and sex, suggesting their biological roles in the two species.

Conclusions

The bacterial microbiomes of field-collected D. marginatus and D. reticulatus were shaped by tick phylogeny and sex. Maternally inherited bacteria were abundant in the two species. These findings are valuable for understanding tick-bacteria interactions, biology and vector competence of ticks.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3582-9) contains supplementary material, which is available to authorized users.

Tissue tropism and metabolic pathways of Midichloria mitochondrii suggest tissue-specific functions in the symbiosis with Ixodes ricinus

A wide range of arthropod species harbour bacterial endosymbionts in various tissues, many of them playing important roles in the fitness and biology of their hosts. In several cases, many different symbionts have been reported to coexist simultaneously within the same host and synergistic or antagonistic interactions can occur between them. While the associations with endosymbiotic bacteria have been widely studied in many insect species, in ticks such interactions are less investigated. The females and immatures of Ixodes ricinus (Ixodidae), the most common hard tick in Europe, harbour the intracellular endosymbiont "Candidatus Midichloria mitochondrii" with a prevalence up to 100%, suggesting a mutualistic relationship. Considering that the tissue distribution of a symbiont might be indicative of its functional role in the physiology of the host, we investigated M. mitochondrii specific localization pattern and the corresponding abundance in selected organs of I. ricinus females. We paired these experiments with in silico analysis of the metabolic pathways of M. mitochondrii, inferred from the available genome sequence, and additionally compared the presence of these pathways in seven other symbionts commonly harboured by ticks to try to obtain a comparative understanding of their biological effects on the tick hosts. M. mitochondrii was found to be abundant in ovaries and tracheae of unfed I. ricinus, and in ovaries, Malpighian tubules and salivary glands of semi-engorged females. These results, together with the in silico metabolic reconstruction allow to hypothesize that the bacterium could play multiple tissue-specific roles in the host, both enhancing the host fitness (supplying essential nutrients, enhancing the reproductive fitness, helping in the anti-oxidative defence, in the energy production and in the maintenance of homeostasis and water balance) and/or for ensuring its presence in the host population (nutrients acquisition, vertical and horizontal transmission). The ability of M. mitochondrii to colonize different tissues allows to speculate that distinctive sub-populations may display different specializations in accordance with tissue tropism. Our hypotheses should be corroborated with future nutritional and physiological experiments for a better understanding of the mechanisms underlying this symbiotic interaction.

Tissue localization of Coxiella-like endosymbionts in three European tick species through fluorescence in situ hybridization

Ticks are commonly infected by Coxiella-like endosymbionts (Coxiella-LE) which are thought to supply missing B vitamin nutrients required for blood digestion.While this nutritional symbiosis is essential for the survival and reproduction of infected tick species, our knowledge of where Coxiella-LE is localized in tick tissues is partial at best since previous studies have focused on a limited number of Asian or American tick species. To fill this gap, we investigated the tissue localization of Coxiella-LE in three European tick species, Ornithodoros maritimus, Dermacentor marginatus and Ixodes hexagonus, using a diagnostic fluorescence in situ hybridization (FISH) assay, combined with PCR-based detection. Specific fluorescent foci were observed in several tick tissues. We visualized a pronounced tissue tropism of Coxiella-LE for tick ovaries and Malpighian tubules, a pattern suggestive of a high degree of lifestyle specialization toward mutualism: infection of the ovaries is indicative of transovarial transmission, whereas infection of the Malpighian tubules suggests a nutritional function. We postulate that Malpighian tubules are key organs for the nutritional symbiosis, notably the synthesis of B vitamins by Coxiella-LE, whereas the infection of the ovaries ensures vertical transmission of the symbionts to future generations. We also detected occasional infections in other organs, such as salivary glands and the midgut. Finally, we discuss the potential significance of the different tissue tropism for tick biology.

Phylogenetics of the Spiroplasma ixodetis endosymbiont reveals past transfers between ticks and other arthropods

The bacterium Spiroplasma ixodetis is a maternally inherited endosymbiont primarily described from ticks but also found widespread across other arthropods. While it has been identified as a male-killing agent in some insect species, the consequences of infection with S. ixodetis in ticks are entirely unknown, and it is unclear how this endosymbiont spreads across tick species. Here, we have investigated this aspect through the examination of the diversity and evolutionary history of S. ixodetis infections in 12 tick species and 12 other arthropod species. Using a multi-locus typing approach, we identified that ticks harbor a substantial diversity of divergent S. ixodetis strains. Phylogenetic investigations revealed that these S. ixodetis strains do not cluster within a tick-specific subclade but rather exhibit distinct evolutionary origins. In their past, these strains have undergone repeated horizontal transfers between ticks and other arthropods, including aphids and flies. This diversity pattern strongly suggests that maternal inheritance and horizontal transfers are key drivers of S. ixodetis spread, dictating global incidence of infections across tick communities. We do not, however, detect evidence of S. ixodetis-based male-killing since we observed that infections were widely present in both males and females across populations of the African blue tick Rhipicephalus decoloratus.

Endosymbionts Alter Larva-to-Nymph Transstadial Transmission of Babesia microti in Rhipicephalus haemaphysaloides Ticks

Maternally inherited endosymbionts inhabit a variety of arthropods. Some of them can protect the arthropod host against a wide range of pathogens. However, very little is known about the association between endosymbionts and pathogen susceptibility in ticks. The present study investigated the effect of endosymbionts on larva-to-nymph transstadial transmission of Babesia microti by Rhipicephalus haemaphysaloides ticks. Engorged female ticks were injected with PBS, ciprofloxacin or kanamycin. The offspring larvae were used to infest B. microti-positive mice. Prevalence of B. microti among the nymphs in different treatment groups and its association with endosymbiont density in the larvae were analyzed. The results showed that the prevalence of B. microti in the kanamycin-treated group (63.9%, 95% confidence interval (CI): 52.8–75.0%) was higher than that in the PBS (23.6%, 95% CI: 13.8–33.4%) or ciprofloxacin-treated (25.0%, 95% CI: 15.0–35.0%) groups. This increased prevalence was associated with reduced density of Coxiella-like endosymbiont but was not related to the density of Rickettsia-like endosymbiont. No direct evidence has previously been reported about the impact of Coxiella-like endosymbiont on pathogen susceptibility in ticks. This study reveals that endosymbionts are potentially important defensive symbionts of R. haemaphysaloides which may influence the colonization or susceptibility of B. microti in the tick host.

Tissue Localization and Variation of Major Symbionts in Haemaphysalis longicornis, Rhipicephalus haemaphysaloides, and Dermacentor silvarum in China

Ticks are important disease vectors, as they transmit a variety of human and animal pathogens worldwide. Symbionts that coevolved with ticks confer crucial benefits to their host in nutrition metabolism, fecundity, and vector competence. Although over 100 tick species have been identified in China, general information on tick symbiosis is limited. Here, we visualized the tissue distribution of Coxiella sp. and Rickettsia sp. in lab-reared Haemaphysalis longicornis and Rhipicephalus haemaphysaloides by fluorescent in situ hybridization. We found that Coxiella sp. colonized exclusively the Malpighian tubules and ovaries of H. longicornis, while Rickettsia sp. additionally colonized the midgut of R. haemaphysaloides We also investigated the population structure of microbiota in Dermacentor silvarum ticks collected from Inner Mongolia, China, and found that Coxiella, Rickettsia, and Pseudomonas are the three dominant genera. No significant difference in microbiota composition was found between male and female D. silvarum ticks. We again analyzed the tissue localization of Coxiella sp. and Rickettsia sp. and found that they displayed tissue tropisms similar to those in R. haemaphysaloides, except that Rickettsia sp. colonized the nuclei of spermatids instead of ovaries in D. silvarum Altogether, our results suggest that Coxiella sp. and Rickettsia sp. are the main symbionts in the three ticks and reside primarily in midgut, Malpighian tubules, and reproductive tissues, but their tissue distribution varies in association with species and sexes.IMPORTANCE Tick-borne diseases constitute a major public health burden, as they are increasing in frequency and severity worldwide. The presence of symbionts helps ticks to metabolize nutrients, promotes fecundity, and influences pathogen infections. Increasing numbers of tick-borne pathogens have been identified in China; however, knowledge of native ticks, especially tick symbiosis, is limited. In this study, we analyze the distribution of Coxiella sp. and Rickettsia sp. in tissues of laboratory-reared Haemaphysalis longicornis and Rhipicephalus haemaphysaloides and field-collected Dermacentor silvarum We found that the localization patterns of Coxiella sp. in three Chinese tick species were similar to those of other tick species. We also found a previously undefined intracellular localization of Rickettsia sp. in tick midgut and spermatids. In addition, we demonstrate that tissue tropisms of symbionts vary between species and sexes. Our findings provide new insights into the tissue localization of symbionts in native Chinese ticks and pave the way for further understanding of their functional capabilities and symbiotic interactions with ticks.

Effects of antibiotic treatment on the fecundity of Rhipicephalus haemaphysaloides ticks

BACKGROUND

Endosymbiotic bacteria inhabit a variety of arthropods including ticks and may have multiple effects on the host's survival, reproduction or pathogen acquisition and transmission. Rhipicephalus haemaphysaloides is one of the most widely distributed tick species in China. The symbiotic bacteria composition and their impacts to R. haemaphysaloides ticks have not been studied. The present study investigated the composition of microbial community in R. haemaphysaloides ticks and then assessed the effects of endosymbionts on the host's fecundity by antibiotic treatment experiments.

METHODS

The microbial population of female and male R. haemaphysaloides ticks was analyzed using Illumina Miseq sequencing of 16S rRNA gene. Thirty engorged female ticks were then randomly divided into five groups and injected with ampicillin, ciprofloxacin, kanamycin, tetracycline, or phosphate-buffered solution (PBS), respectively. Effects of antibiotic treatments on maternal oviposition, egg hatching and density of endosymbionts were evaluated.

RESULTS

Illumina Miseq sequencing showed that Coxiella and Rickettsia were the predominant bacterial genera inhabiting R. haemaphysaloides ticks. Antibiotic treatment experiments found that kanamycin reduced the density of Coxiella-like endosymbiont (Coxiella-LE hereafter) in eggs, ciprofloxacin reduced the density of Rickettsia-like endosymbiont (Rickettsia-LE), and tetracycline had effect on both endosymbionts, while ampicillin affected neither. Meanwhile hatching rates of eggs were observed to decrease greatly in the kanamycin or tetracycline-treated group but maintained in the ampicillin or ciprofloxacin-treated group. Furthermore, the reduced hatching rates were found to be associated with density of Coxiella-LE in eggs.

CONCLUSIONS

The findings indicate that Coxiella-LE is essential for the reproduction of R. haemaphysaloides ticks, and that kanamycin can be used to study the role of Coxiella-LE on ticks.