Wolbachia Host Research Articles

Wolbachia Replication and Host Cell Division in Aedes albopictus

Wolbachia pipientis is an obligate intracellular endosymbiont of a range of arthropod species. The microbe is best known for its manipulations of host reproduction that include inducing cytoplasmic incompatibility, parthenogenesis, feminization, and male-killing. Like other vertically transmitted intracellular symbionts, Wolbachia's replication rate must not outpace that of its host cells if it is to remain benign. The mosquito Aedes albopictus is naturally infected both singly and doubly with different strains of Wolbachia pipientis. During diapause in mosquito eggs, no host cell division is believed to occur. Further development is triggered only by subsequent exposure of the egg to water. This study uses diapause in Wolbachia-infected Aedes albopictus eggs to determine whether symbiont replication slows or stops when host cell division ceases or whether it continues at a low but constant rate. We have shown that Wolbachia densities in eggs are greatest during embryonation and then decline throughout diapause, suggesting that Wolbachia replication is dependent on host cell replication.

Diversity of Wolbachia endosymbionts in heteropteran bugs.

An extensive survey of Wolbachia endosymbionts in Japanese terrestrial heteropteran bugs was performed by PCR detection with universal primers for wsp and ftsZ genes of Wolbachia, cloning of the PCR products, restriction fragment length polymorphism analysis of infecting Wolbachia types, and molecular phylogenetic characterization of all the detected Wolbachia strains. Of 134 heteropteran species from 19 families examined, Wolbachia infection was detected in 47 species from 13 families. From the 47 species, 59 Wolbachia strains were identified. Of the 59 strains, 16 and 43 were assigned to A group and B group in the Wolbachia phylogeny, respectively. The 47 species of Wolbachia-infected bugs were classified into 8 species with A infection, 28 species with B infection, 2 species with AA infection, 3 species with AB infection, 5 species with BB infection, and 1 species with ABB infection. Molecular phylogenetic analysis showed little congruence between Wolbachia phylogeny and host systematics, suggesting frequent horizontal transfers of Wolbachia in the evolutionary course of the Heteroptera. The phylogenetic analysis also revealed several novel lineages of Wolbachia. Based on statistical analyses of the multiple infections, we propose a hypothetical view that, in the heteropteran bugs, interactions between coinfecting Wolbachia strains are generally not intense and that Wolbachia coinfections have been established through a stochastic process probably depending on occasional horizontal transfers.

Characterization of non-cytoplasmic incompatibility inducing Wolbachia in two continental African populations of Drosophila simulans.

Wolbachia is an endocellular bacterium infecting arthropods and nematodes. In arthropods, it invades host populations through various mechanisms, affecting host reproduction, the most common of which being cytoplasmic incompatibility (CI). CI is an embryonic mortality occurring when infected males mate with uninfected females or females infected by a different Wolbachia strain. This phenomenon is observed in Drosophila simulans, an intensively studied Wolbachia host, harbouring at least five distinct bacterial strains. In this study, we investigate various aspects of the Wolbachia infections occurring in two continental African populations of D. simulans: CI phenotype, phylogenetic position based on the wsp gene and associated mitochondrial haplotype. From the East African population (Tanzania), we show that (i) the siIII mitochondrial haplotype occurs in continental populations, which was unexpected based on the current views of D. simulans biogeography, (ii) the wKi strain (that rescues from CI while being unable to induce it) is very closely related to the CI-inducing strain wNo, (iii) wKi and wNo might not derive from a unique infection event, and (iv) wKi is likely to represent the same entity as the previously described wMa variant. In the West African population (Cameroon), the Wolbachia infection was found identical to the previously described wAu, which does not induce CI. This finding supports the view that wAu might be an ancient infection in D. simulans.

The effect of Wolbachia-induced cytoplasmic incompatibility on host population size in natural and manipulated systems.

Obligate, intracellular bacteria of the genus Wolbachia often behave as reproductive parasites by manipulating host reproduction to enhance their vertical transmission. One of these reproductive manipulations, cytoplasmic incompatibility, causes a reduction in egg-hatch rate in crosses between individuals with differing infections. Applied strategies based upon cytoplasmic incompatibility have been proposed for both the suppression and replacement of host populations. As Wolbachia infections occur within a broad range of invertebrates, these strategies are potentially applicable to a variety of medically and economically important insects. Here, we examine the interaction between Wolbachia infection frequency and host population size. We use a model to describe natural invasions of Wolbachia infections, artificial releases of infected hosts and releases of sterile males, as part of a traditional sterile insect technique programme. Model simulations demonstrate the importance of understanding the reproductive rate and intraspecific competition type of the targeted population, showing that releases of sterile or incompatible individuals may cause an undesired increase in the adult number. In addition, the model suggests a novel applied strategy that employs Wolbachia infections to suppress host populations. Releases of Wolbachia-infected hosts can be used to sustain artificially an unstable coexistence of multiple incompatible infections within a host population, allowing the host population size to be reduced, maintained at low levels, or eliminated.

Male-Killing, Nematode Infections, Bacteriophage Infection, and Virulence of Cytoplasmic Bacteria in the GenusWolbachia

▪ Abstract Wolbachia bacteria are cytoplasmic endosymbionts with a wide range of effects on their hosts and are known to infect two major invertebrate groups, arthropods and nematodes. In arthropods Wolbachia alter host reproduction, causing unidirectional and bidirectional cytoplasmic incompatibility, parthenogenesis, feminization, and embryonic male killing. Wolbachia variation in reproductive effects is indicative of a high degree of evolutionary plasticity. As many as 75% of arthropods may be infected with Wolbachia, which in addition to affecting reproduction, can also directly affect host fitness by either increasing or decreasing survival and fecundity. We review the dynamics of embryonic male-killing, including effects on insect mating behavior, as well as the distribution and implication of Wolbachia infections in filarial nematodes.Arthropod host–Wolbachia phylogenies are not congruent, which is suggestive of horizontal transmission. The opposite has been shown in nematode-Wolbachia phylogenies, indicative of long-term association and vertical transmission. Multiple levels of parasitism within arthropods may promote horizontal transmission. Bacteriophage WO has recently been identified and is found in all Wolbachia-infected insect hosts so far examined. Extensive horizontal transmission of the phage occurs between different Wolbachia strains within a host as well as between Wolbachia in different hosts. The phage genome may carry genes important in determining both the effect of Wolbachia on arthropod host reproduction and host fitness and fecundity. The extensive horizontal transmission of the phage may explain the plasticity of Wolbachia's effect on arthropod hosts.

Wolbachia diversity in the Porcellionides pruinosus complex of species (Crustacea: Oniscidea): evidence for host-dependent patterns of infection.

Porcellionides pruinosus is a cosmopolitan woodlouse. It is known to exhibit patterns of geographical variation between populations, and has been suspected to consist of several very closely related species. This species was found to carry Wolbachia endosymbionts, alpha-proteobacteria which are known to modify the reproduction of their crustacean hosts by inducing cytoplasmic incompatibility or feminization. In the P. pruinosus complex, Wolbachia induced feminization, but two different patterns of infection were reported: high prevalence and presence of infected males, or low prevalence and absence of infected males. In this study we investigated nine populations described as Porcellionides pruinosus carrying different Wolbachia strains, with the aim of investigating the possibility of coevolution between symbionts and hosts. Molecular analyses were carried out on both Wolbachia DNA (wsp gene) and host mitochondrial DNA (mt LSU rDNA). We show that (1) the nine host populations exhibited a high genetic differentiation so that they have to be split into two sibling species; (2) three different Wolbachia strains were found in the host complex but were not species-specific; and (3) the pattern of infection by Wolbachia was more host-dependent than symbiont-dependent.

Did Wolbachia cross the border?

Wolbachia is an obligate intracellular bacterium, widespread in arthropods, that is vertically transmitted from mothers to offspring. Owing to this mode of inheritance, selection favours Wolbachia variants that increase the fitness of infected females, regardless of a possible detrimental effect on infected males. Under such a selective pressure, Wolbachia have evolved a wide variety of interesting phenomena (e.g. male killing, MK; feminization, F; thelytokous parthenogenesis, TP; and cytoplasmic incompatibility, CI) that favour the initial spread, and then maintenance of Wolbachia in uninfected populations. The evolutionary stability of Wolbachia–host associations strongly depends on which phenotype is induced. TP is probably the most irreversible: male functions tend to degenerate, because they are not subject to any selective pressure in parthenogenetic lines. Once males are nonfunctional, a loss of Wolbachia (i.e. a return to sexual reproduction) is impossible. For MK, F and CI, selection (if resistance host genes evolve) or drift, can eventually lead to a loss of Wolbachia infection. However, a new study suggests that Wolbachia can become obligatory mutualists 1 Dedeine F. et al. Removing symbiotic Wolbachia bacteria specifically inhibits oogenesis in a parasitic wasp. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 6247-6252 Crossref PubMed Scopus (342) Google Scholar . Dedeine et al. report that, in the hymenopteran parasitoid Asobara tabida, eliminating Wolbachia inhibits oogenesis, resulting in sterility. We see two possible evolutionary scenarios to explain this phenotype.