Evolutionary history of <Emphasis Type="Italic">Wolbachia</Emphasis> infections in the fire ant <Emphasis Type="Italic">Solenopsis invicta</Emphasis>

Background  

Wolbachia are endosymbiotic bacteria that commonly infect numerous arthropods. Despite their broad taxonomic distribution, the transmission patterns of these bacteria within and among host species are not well understood. We sequenced a portion of the wsp gene from the Wolbachia genome infecting 138 individuals from eleven geographically distributed native populations of the fire ant Solenopsis invicta. We then compared these wsp sequence data to patterns of mitochondrial DNA (mtDNA) variation of both infected and uninfected host individuals to infer the transmission patterns of Wolbachia in S. invicta.     

Clarithromycin and Amoxicillin Susceptibility of Helicobacter pylori Strains Isolated from Adult Patients with Gastric or Duodenal Ulcer in Italy

Wolbachia endosymbiotic bacteria are widespread in arthropods and are also present in filarial nematodes. Almost all filarial species so far examined have been found to harbor these endosymbionts. The sequences of only three genes have been published for nematode Wolbachia (i.e., the genes coding for the proteins FtsZ and catalase and for 16S rRNA). Here we present the sequences of the genes coding for the Wolbachia surface protein (WSP) from the endosymbionts of eight species of filaria. Complete gene sequences were obtained from the endosymbionts of two different species, Dirofilaria immitis and Brugia malayi. These sequences allowed us to design general primers for amplification of the wsp gene from the Wolbachia of all filarial species examined. For these species, partial WSP sequences (about 600 base pairs) were obtained with these primers. Phylogenetic analysis groups these nematode wsp sequences into a coherent cluster. Within the nematode cluster, wsp-based Wolbachia phylogeny matches a previous phylogeny obtained with ftsZ gene sequences, with a good consistency of the phylogeny of hosts (nematodes) and symbionts (Wolbachia). In addition, different individuals of the same host species (Dirofilaria immitis and Wuchereria bancrofti) show identical wsp gene sequences. Received: 10 January 2000 / Accepted: 22 February 2000     

Outer membrane proteins can be simply identified using secondary structure element alignment

Background  

Outer membrane proteins (OMPs) are frequently found in the outer membranes of gram-negative bacteria, mitochondria and chloroplasts and have been found to play diverse functional roles. Computational discrimination of OMPs from globular proteins and other types of membrane proteins is helpful to accelerate new genome annotation and drug discovery.     

Maintenance of adaptive differentiation by Wolbachia induced bidirectional cytoplasmic incompatibility: the importance of sib-mating and genetic systems

Background  

Bacteria of the genus Wolbachia are reproductive parasites widespread among arthropods. The most common effect arising from the presence of Wolbachia in a population is Cytoplasmic Incompatibility (CI), whereby postmating reproductive isolation occurs in crosses between an infected male and an uninfected female, or when a male is infected with a different strain of Wolbachia to that of the female (bidirectional CI). Previous theoretical models have demonstrated that bidirectional CI can contribute to the genetic divergence of populations in haploid and diploid organisms. However, haplodiploid organisms were not considered in these models even though they include Nasonia parasitoid wasps – the best example of the implication of Wolbachia in ongoing speciation. Moreover, previous work did not investigate inbreeding mating systems, which are frequently observed in arthropod species.     

Multiple endosymbionts in populations of the ant <Emphasis Type="Italic">Formica cinerea</Emphasis>

Background  

Many insects, including ants, are infected by maternally inherited Wolbachia endosymbiotic bacteria though other secondary endosymbionts have not been reported in ants. It has been suggested that the ability of Wolbachia to invade and remain in an ant population depends on the number of coexisting queens in a colony. We study the genetic and social structure of populations in the ant Formica cinerea which is known to have populations with either monogynous or polygynous colonies. We screen populations for several endosymbiotic bacteria to evaluate the presence of different endosymbionts, possible association between their prevalence and the social structure, and the association between endosymbiont prevalence and genetic differentiation of ant populations.     

Antibiotic treatment leads to the elimination of Wolbachia endosymbionts and sterility in the diplodiploid collembolan Folsomia candida

Background  

Wolbachia is an extremely widespread bacterial endosymbiont of arthropods and nematodes that causes a variety of reproductive peculiarities. Parthenogenesis is one such peculiarity but it has been hypothesised that this phenomenon may be functionally restricted to organisms that employ haplodiploid sex determination. Using two antibiotics, tetracycline and rifampicin, we attempted to eliminate Wolbachia from the diplodiploid host Folsomia candida, a species of springtail which is a widely used study organism.     

PpiD is a player in the network of periplasmic chaperones in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Background  

The inner membrane-anchored periplasmic folding factor PpiD is described as a parvulin-like peptidyl prolyl isomerase (PPIase) that assists in the maturation of the major beta-barrel outer membrane proteins (OMPs) of Escherichia coli. More recent work however, calls these findings into question. Here, we re-examined the role of PpiD in the E. coli periplasm by analyzing its functional interplay with other folding factors that influence OMP maturation as well as general protein folding in the periplasmic compartment of the cell, such as SurA, Skp, and DegP.     

Ankyrin repeat domain-encoding genes in the wPip strain of Wolbachia from the Culex pipiens group

Background  

Wolbachia are obligate endosymbiotic bacteria maternally transmitted through the egg cytoplasm that are responsible for several reproductive disorders in their insect hosts, such as cytoplasmic incompatibility (CI) in infected mosquitoes. Species in the Culex pipiens complex display an unusually high number of Wolbachia-induced crossing types, and based on present data, only the wPip strain is present.     

Comparative analysis of Wolbachia surface protein in D. melanoagster, A. tabida and B. malayi

Wolbachia surface protein (WSP) is an eight beta-barrel transmembrane structure which participates in host immune response, cell proliferation, pathogenicity and controlled cell death program. The protein has four extracellular loops containing hyper variable regions separated by conserved regions. The WSP structure is homologous to Neisseria surface protein (Nsp A) which has about 34% similarity including antigenic variation and hydrophilicity. Recombination has a large impact on diversity of this protein including positive selection which is major constraint on protein evolution. The molecular mechanism through which Wolbachia induces various reproductive anomalies is unclear; a key feature observed for such anomalies might be because of Wolbachia undergoing extensive recombination. In Wolbachia, increased recombination is observed in ankyrin proteins, surface proteins and in some hypothetical proteins. Genetic divergence is extensive in the WSP gene, WSP is known to be a chimeric protein involved in host-symbiont interactions. Here we predicted the structural and functional variations in WSP sequences of Wolbachia present in D. melanogaster, A. tabida and in B. malayi.     

The diversity of reproductive parasites among arthropods: <Emphasis Type="Italic">Wolbachia</Emphasis>do not walk alone

Background  

Inherited bacteria have come to be recognised as important components of arthropod biology. In addition to mutualistic symbioses, a range of other inherited bacteria are known to act either as reproductive parasites or as secondary symbionts. Whilst the incidence of the α-proteobacterium Wolbachia is relatively well established, the current knowledge of other inherited bacteria is much weaker. Here, we tested 136 arthropod species for a range of inherited bacteria known to demonstrate reproductive parasitism, sampling each species more intensively than in past surveys.     

Absence of <Emphasis Type="Italic">Wolbachia</Emphasis> in Nonfilariid Worms Parasitizing Arthropods

Wolbachia are strictly intracellular maternally inherited α-proteobacteria, largely widespread among arthropods and filariids (i.e., filarial nematodes). Wolbachia capacities to infect new host species have been greatly evidenced and the transfer of Wolbachia between arthropods and filariids has probably occurred more than once. Interestingly, among nematode species, Wolbachia infection was found in filariids but not in closely related lineages. Their occurrence in filariids has been supposed a consequence of the parasitic lifestyle of worms within Wolbachia-infected arthropods, implying that nonfilariid worms parasitizing arthropods are also likely to be infected by some Wolbachia acquired from their hosts. To further investigate this hypothesis, we have examined seven species of nonfilariid worms of Nematoda and Nematomorpha phyla, all interacting intimately with arthropods. Wolbachia infection in nonfilariid parasitic worms was never detected by polymerase chain reaction assays of the 16S rDNA and wsp genes. By contrast, some arthropod hosts are well infected by Wolbachia of the B supergroup. Then the intimate contact with infected arthropods is not a sufficient condition to explain the Wolbachia occurrence in filariids and could underline a physiological singularity or a particular evolutionary event to acquire and maintain Wolbachia infection.     

Effects of a sex-ratio distorting endosymbiont on mtDNA variation in a global insect pest

Background  

Patterns of mtDNA variation within a species reflect long-term population structure, but may also be influenced by maternally inherited endosymbionts, such as Wolbachia. These bacteria often alter host reproductive biology and can drive particular mtDNA haplotypes through populations. We investigated the impacts of Wolbachia infection and geography on mtDNA variation in the diamondback moth, a major global pest whose geographic distribution reflects both natural processes and transport via human agricultural activities.     

Influence of oxidative homeostasis on bacterial density and cost of infection in Drosophila–Wolbachia symbioses

The evolution of symbioses along the continuum between parasitism and mutualism can be influenced by the oxidative homeostasis, that is the balance between reactive oxygen species (ROS) and antioxidant molecules. Indeed, ROS can contribute to the host immune defence to regulate symbiont populations, but are also toxic. This interplay between ROS and symbiosis is notably exemplified by recent results in arthropod–Wolbachia interactions. Wolbachia are symbiotic bacteria involved in a wide range of interactions with their arthropods hosts, from facultative, parasitic associations to obligatory, mutualistic ones. In this study, we used Drosophila–Wolbachia associations to determine whether the oxidative homeostasis plays a role in explaining the differences between phenotypically distinct arthropod–Wolbachia symbioses. We used Drosophila lines with different Wolbachia infections and measured the effects of pro‐oxidant (paraquat) and antioxidant (glutathione) treatments on the Wolbachia density and the host survival. We show that experimental manipulations of the oxidative homeostasis can reduce the cost of the infection through its effect on Wolbachia density. We discuss the implication of this result from an evolutionary perspective and argue that the oxidative homeostasis could underlie the evolution of tolerance and dependence on Wolbachia.     

Serum antibody responses to Wolbachia surface protein in patients with human lymphatic filariasis

Wolbachia surface protein (WSP), which is the most abundantly expressed protein of Wolbachia from the human filarial parasite Brugia malayi, was chosen for the present study. B‐cell epitope prediction of the WSP protein sequence indicates a high antigenicity, surface probability and hydrophilicity by DNA STAR software analysis. ProPred analysis suggests the presence of HLA class II binding regions in the WSP protein that contribute to T‐cell responses and isotype reactivity. In order to validate these findings, the gene coding for endosymbiont WSP was PCR‐amplified from the genomic DNA of the human filarial parasite Brugia malayi and cloned in T‐7 expression vector pRSET‐A. Western blot and ELISA at the total IgG level with recombiant WSP indicated a significantly elevated reactivity in CP compared to MF, EN and NEN individuals. Isotype ELISA also suggested an elevated reactivity in CP patients at the IgG1 level. In contrast, WSP‐specific IgG4 levels were found to be elevated in MF patients compared to CP and EN. Besides this, WSP‐specific IgE levels indicated an elevated reactivity in CP and MF patients compared to normals. Observations from ELISA supported the in silico predictions that indicate the presence of B‐ and T‐cell epitopes. Hence, a combinatorial approach of in silico predictions and wet‐lab studies provides interesting insights into the role of Wolbachia proteins in filarial pathogenesis.     

New insights into the evolution of Wolbachia infections in filarial nematodes inferred from a large range of screened species

Background

Wolbachia are intriguing symbiotic endobacteria with a peculiar host range that includes arthropods and a single nematode family, the Onchocercidae encompassing agents of filariases. This raises the question of the origin of infection in filariae. Wolbachia infect the female germline and the hypodermis. Some evidences lead to the theory that Wolbachia act as mutualist and coevolved with filariae from one infection event: their removal sterilizes female filariae; all the specimens of a positive species are infected; Wolbachia are vertically inherited; a few species lost the symbiont. However, most data on Wolbachia and filaria relationships derive from studies on few species of Onchocercinae and Dirofilariinae, from mammals.

Methodology/Principal Findings

We investigated the Wolbachia distribution testing 35 filarial species, including 28 species and 7 genera and/or subgenera newly screened, using PCR, immunohistochemical staining, whole mount fluorescent analysis, and cocladogenesis analysis. (i) Among the newly screened Onchocercinae from mammals eight species harbour Wolbachia but for some of them, bacteria are absent in the hypodermis, or in variable density. (ii) Wolbachia are not detected in the pathological model Monanema martini and in 8, upon 9, species of Cercopithifilaria. (iii) Supergroup F Wolbachia is identified in two newly screened Mansonella species and in Cercopithifilaria japonica. (iv) Type F Wolbachia infect the intestinal cells and somatic female genital tract. (v) Among Oswaldofilariinae, Waltonellinae and Splendidofilariinae, from saurian, anuran and bird respectively, Wolbachia are not detected.

Conclusions/Significance

The absence of Wolbachia in 63% of onchocercids, notably in the ancestral Oswaldofilariinae estimated 140 mya old, the diverse tissues or specimens distribution, and a recent lateral transfer in supergroup F Wolbachia, modify the current view on the role and evolution of the endosymbiont and their hosts. Further genomic analyses on some of the newly sampled species are welcomed to decipher the open questions.     

Intragenomic conflict in populations infected by Parthenogenesis Inducing <Emphasis Type="Italic">Wolbachia</Emphasis> ends with irreversible loss of sexual reproduction

Background  

The maternally inherited, bacterial symbiont, parthenogenesis inducing (PI) Wolbachia, causes females in some haplodiploid insects to produce daughters from both fertilized and unfertilized eggs. The symbionts, with their maternal inheritance, benefit from inducing the production of exclusively daughters, however the optimal sex ratio for the nuclear genome is more male-biased. Here we examine through models how an infection with PI-Wolbachia in a previously uninfected population leads to a genomic conflict between PI-Wolbachia and the nuclear genome. In most natural populations infected with PI-Wolbachia the infection has gone to fixation and sexual reproduction is impossible, specifically because the females have lost their ability to fertilize eggs, even when mated with functional males.     

<Emphasis Type="Italic">Wolbachia pipientis</Emphasis> in Australian Spiders

Wolbachia pipientis is an endosymbiotic bacterium common to arthropods and filarial nematodes. This study presents the first survey and characterization of Wolbachia pipientis that infect spiders. All spiders were collected from Queensland, Australia during 2002–2003 and screened for Wolbachia infection using PCR approaches. The Wolbachia strains present in the spiders are diverse, paraphyletic, and for the most part closely related to strains that infect insects. We have also identified several spider Wolbachia strains that form a lineage outside the currently recognized six main Wolbachia supergroups (A–F). Incongruence between spider and Wolbachia phylogenies indicates a history of horizontal transmission of the bacterium in these host taxa. Like other arthropods, spiders are capable of harboring multiple Wolbachia strains.     

Interactions between flagellar and type III secretion proteins in <Emphasis Type="Italic">Chlamydia pneumoniae</Emphasis>

Background  

Flagellar secretion systems are utilized by a wide variety of bacteria to construct the flagellum, a conserved apparatus that allows for migration towards non-hostile, nutrient rich environments. Chlamydia pneumoniae is an obligate, intracellular pathogen whose genome contains at least three orthologs of flagellar proteins, namely FliI, FlhA and FliF, but the role of these proteins remains unknown.     

Cytoplasmic incompatibility involving <Emphasis Type="Italic">Cardinium</Emphasis> and <Emphasis Type="Italic">Wolbachia</Emphasis> in the white-backed planthopper <Emphasis Type="Italic">Sogatella furcifera</Emphasis> (Hemiptera: Delphacidae)

Cytoplasmic incompatibility (CI) is a reproductive phenotype induced by bacterial endosymbionts in arthropods. Measured as a reduction in egg hatchability resulting from the crossing of uninfected females with bacteria-infected males, CI increases the frequency of bacteria-infected hosts by restricting the fertilization opportunities of uninfected hosts in populations. Wolbachia, a type of alpha-proteobacteria, is well known as a CI inducer in a wide range of arthropod species, while Cardinium, a member of the phylum Bacteroidetes, is known to cause CI in one wasp and three spider mite species. In this study, dual infection with Cardinium and Wolbachia induced strong CI in a single host, Sogatella furcifera (Horváth), a planthopper species that is naturally infected with both bacteria. Specifically, infection with Cardinium alone was found to cause a 76 % reduction in egg development, and dual infection with Cardinium and Wolbachia a 96 % reduction, indicating that Cardinium induces CI and the dual infection raises the CI level. This study was the first to document reproductive alteration by Cardinium in a diploid host species.     

Host tissues as microhabitats for Wolbachia and quantitative insights into the bacterial community in terrestrial isopods

Animal–bacterial symbioses are highly dynamic in terms of multipartite interactions, both between the host and its symbionts as well as between the different bacteria constituting the symbiotic community. These interactions will be reflected by the titres of the individual bacterial taxa, for example via host regulation of bacterial loads or competition for resources between symbionts. Moreover, different host tissues represent heterogeneous microhabitats for bacteria, meaning that host‐associated bacteria might establish tissue‐specific bacterial communities. Wolbachia are widespread endosymbiotic bacteria, infecting a large number of arthropods and filarial nematodes. However, relatively little is known regarding direct interactions between Wolbachia and other bacteria. This study represents the first quantitative investigation of tissue‐specific Wolbachia–microbiota interactions in the terrestrial isopod Armadillidium vulgare. To this end, we obtained a more complete picture of the Wolbachia distribution patterns across all major host tissues, integrating all three feminizing Wolbachia strains (wVulM, wVulC, wVulP) identified to date in this host. Interestingly, the different Wolbachia strains exhibited strain‐specific tissue distribution patterns, with wVulM reaching lower titres in most tissues. These patterns were consistent across different host genetic backgrounds and might reflect different co‐evolutionary histories between the Wolbachia strains and A. vulgare. Moreover, Wolbachia‐infected females carried higher total bacterial loads in several, but not all, tissues, irrespective of the Wolbachia strain. Taken together, this quantitative approach indicates that Wolbachia is part of a potentially more diverse bacterial community, as exemplified by the presence of highly abundant bacterial taxa in the midgut caeca of several A. vulgare populations.