Molecular evolution and phylogenetic utility of Wolbachia ftsZ and wsp gene sequences with special reference to the origin of male-killing.

A detailed assessment of the evolution and phylogenetic utility of two genes, ftsZ and wsp, was used to investigate the origin of male-killing Wolbachia, previously isolated from the ladybird Adalia bipunctata and the butterfly Acraea encedon. The analysis included almost all available sequences of B-group Wolbachia and two outgroup taxa and showed that (1) the two gene regions differ in phylogenetic utility, (2) sequence variation is here correlated with phylogenetic information content, (3) both genes show significant rate heterogeneity between lineages, (4) increased substitution rates are associated with homoplasy in the data, (5) wsp sequences of some taxa appear to be subject to positive selection, and (6) only a limited number of clades can be inferred with confidence due to either lack of phylogenetic information or the presence of homoplasy. With respect to the evolution of male-killing, the two genes nevertheless seemed to provide unbiased information. However, they consistently produce contradictory results. Current data therefore do not permit clarification of the origin of this behavior. In addition, A. bipunctata was found to be a host to two recently diverged strains of male-killing Wolbachia that showed increased substitution rates for both genes. Moreover, the wsp gene, which codes for an outer membrane protein, was found to be subject to positive selection in these taxa. These findings were postulated to be the product of high selection pressures due to antagonistic host-symbiont interactions in this ladybird species. In conclusion, our study demonstrates that the results of a detailed phylogenetic analysis, including characterization of the limitations of such an approach, can serve as a valuable basis for an understanding of the evolution of Wolbachia bacteria. Moreover, particular features of gene evolution, such as elevated substitution rates or the presence of positive selection, may provide information about the dynamics of Wolbachia-host associations.

Phylogeny of the arthropod endosymbiont Wolbachia based on the wsp gene.

Bacteria of the genus Wolbachia (Rickettsiae) are widespread in arthropods and can induce cytoplasmic incompatibility (CI), thelytoky (T) or feminization (F) in their host. Recent research on the wsp gene of mainly CI inducing Wolbachia has shown that this gene evolves at a much faster rate than previously sequenced genes such as 16S or ftsZ. As a result this gene appears to be very useful in subdividing the Wolbachia and twelve groups have been distinguished to date. Here we extend the Wolbachia wsp data set with fifteen T-Wolbachia, one F-Wolbachia and three other CI-Wolbachia strains. The results showed: (i) the addition of seven groups; (ii) no relation between host phenotype and Wolbachia phylogenetic position; and (iii) possible horizontal Wolbachia transfer between the moth Ephestia kuehniella and its parasitoid Trichogramma spp.

Cross-order transfer of Wolbachia from Muscidifurax uniraptor (Hymenoptera: Pteromalidae) to Drosophila simulans (Diptera: Drosophilidae).

Bacteria of the genus Wolbachia are widespread in arthropods and can induce different effects on the host such as cytoplasmic incompatibility (CI), thelytoky (T) or feminization (F). In some Wolbachia-infected hosts, no effect (N) has been found. Successful transfer of Wolbachia by microinjection from one host to an uninfected one has been established with CI, F, N-Wolbachia but not with T-Wolbachia. In this paper a transfer experiment of T-Wolbachia from the parasitoid Muscidifurax uniraptor to Drosophila simulans is described. The infection could be detected in the new host for several generations by polymerase chain reaction (PCR). However, no specific effects on the host were detected, and the bacteria were not stably maintained.

Spacer 2 region and 5S rDNA variation of Wolbachia strains involved in cytoplasmic incompatibility or sex-ratio distortion in arthropods.

Bacteria in the genus Wolbachia are widespread in arthropods and can induce sex-ratio distortion or cytoplasmic incompatibility in their hosts. The phylogeny of Wolbachia has been studied using 16S rDNA and the cell cycle gene ftsZ, but sequence variation of those genes is limited. The spacer 2 region (SR2) was amplified to determine whether this region would improve phylogenetic resolution. The SR2 of Wolbachia is 66 bp long, shows higher variation than ftsZ and has very low homology with closely related bacteria. Due to the small length of SR2 of Wolbachia, little phylogenetic information could be retrieved.

Disruption of lysosomal targeting is associated with insecticidal potency of juvenile hormone esterase.

Juvenile hormone esterase (JHE; EC 3.1.1.1), which is intrinsically involved in regulation of development of some insect larvae, is rapidly removed from the hemolymph by the pericardial cells. Lys-29 and Lys-524, which are implicated in the degradation of JHE, were mutated to Arg. Neither the half-life of the modified JHE in the hemolymph nor the catalytic parameters were changed significantly, but when combined, these mutations resulted in apparent failure of lysosomal targeting in the pericardial cell complex. A hypothesis for the mechanism of reduced efficiency of lysosomal targeting is presented. Infection of larvae with a recombinant baculovirus expressing the modified JHE resulted in a 50% reduction in feeding damage compared with larvae infected with the wild-type virus, thus demonstrating improved properties as a biological insecticide. These data demonstrate that alteration of specific residues of JHE that disrupted lysosomal targeting, dramatically increased the insecticidal activity of this protein.

Smoke as a form of personal protection against mosquitos, a field study in Papua New Guinea.

Smoke from burning different kinds of vegetation or wood is often used as a cheap personal protection measure against mosquitos during the evening. To test the efficacy of smoke, a comparative field trial was conducted in the Wosera District, Papua New Guinea. Repellency of smoke from burning wild mango wood (Mangifera spp), leaves from betelnut (Areca catechu), wild ginger (Alpinia spp) and coconut husks (Cocos nutifera) was assessed using man-biting catches. A mosquito species and smoke specific repellency was found. An. karwari was repelled by coconut husks (66% CI 17-86%), ginger (69% CI 25-87%) and betelnut (84% CI 62-94%) leaves. Culicines were repelled by mango wood (57% CI 6-80%), coconut husks (62% CI 18-83%), ginger (75% CI 45-88%) and betelnut (64% CI 22-84%) leaves. For An. koliensis no repellency due to smoke was found. In combination with untreated or impregnated bed-nets, smoke may contribute to a reduction of mosquito transmitted diseases.

Dissimilar expression of Autographa californica multiple nucleocapsid nuclear polyhedrosis virus polyhedrin and p10 genes.

The temporal expression of the Autographa californica multiple nucleocapsid nuclear polyhedrosis virus polyhedrin and p10 genes in Spodoptera frugiperda cells was studied using virus recombinants in which either gene was replaced by the juvenile hormone esterase (JHE) gene of Heliothis virescens. The JHE served as a highly specific and sensitive reporter for gene expression. Activation of the p10 gene followed a pattern different to that of polyhedrin. The p10 gene was activated a few hours earlier than the polyhedrin gene, but its expression reached a lower maximum level. Northern blot analysis complemented and confirmed the results obtained from the JHE assays. Co-infection of sense recombinants and those containing an antisense copy of the JHE gene in place of the polyhedrin or p10 gene resulted in reduced levels of JHE gene expression. These experiments independently supported the hypothesis that the p10 gene promoter is more active at earlier times post-infection than that of the polyhedrin gene. The results also highlight the potential of the antisense strategy as an experimental approach for the study of baculovirus gene regulation and possibly insect metabolism.