Wolbachia infection and cytoplasmic incompatibility in Drosophila species.

Forty-one stocks from 30 Drosophila species were surveyed for Wolbachia infection using PCR technology. D. sechellia and two strains of D. auraria were found to be infected and were tested for the expression of cytoplasmic incompatibility, along with D. ananassae and D. melanogaster strains, which are already known to be infected. D. ananassae and D. melanogaster show levels of incompatibility up to 25%, while D. auraria and D. sechellia exhibit levels of egg mortality approximately 60%. A dot-blot assay using the dnaA sequence as probe was developed to assess the infection levels in individual males that were used in incompatibility crosses. A positive correlation between bacterial density and cytoplasmic incompatibility was observed. The stocks examined can be clustered into at least two groups, depending on the levels of infection relative to the degree of cytoplasmic incompatibility exhibited. One group, containing D. simulans Hawaii, D. sechellia, and D. auraria, exhibits high levels of cytoplasmic incompatibility relative to levels of infection; all the other species and D. simulans Riverside exhibit significantly lower levels of cytoplasmic incompatibility relative to levels of infection. These data show that, in addition to bacterial density, bacterial and/ or host factors also affect the expression of cytoplasmic incompatibility.

A prokaryotic dnaA sequence in Drosophila melanogaster: Wolbachia infection and cytoplasmic incompatibility among laboratory strains.

Using oligonucleotide primers derived from the aligned polypeptide sequences of several prokaryotic dnaA genes, we amplified from Drosophila melanogaster DNA a 557 bp fragment containing a single open reading frame. The predicted peptide sequence shows a significant similarity to previously characterized protein sequences that are encoded by the dnaA genes of several prokaryotes. The dnaA sequences are also detectable by PCR in DNA from Drosophila simulans and Nasonia vitripennis flies which are infected by a symbiotic bacterium assigned to the type species Wolbachia pipientis. A tetracycline treatment that eradicates bacterial parasites from insects, abolishes the dnaA sequences from Drosophila and Nasonia DNA. In addition, dnaA-positive Drosophila melanogaster contain numerous rod-shaped bacteria in embryos, which are abolished in subsequent generations after treatment with tetracycline. Combined with phylogenetic analysis of DnaA and 16S rRNA sequences, these results show that the dnaA cognate comes from Wolbachia. A survey of Drosophila stocks using PCR amplification of dnaA and 16S rRNA sequences showed that Wolbachia is widely spread among D. melanogaster laboratory strains but absent from several established strains of the Mediterranean fruit fly Ceratitis capitata. Evidence is also presented that presence of the bacterium can cause partial cytoplasmic incompatibility between infected and non-infected D. melanogaster strains.