Wolbachia are widespread maternally-transmitted intracellular bacteria that infect most insect species and are able to alter the reproduction of innumerous hosts. The cellular bases of these alterations remain largely unknown. Here we report that Drosophila mauritiana infected with a native Wolbachia wMau strain produces about four times more eggs than the non-infected counterpart. Wolbachia infection leads to an increase in the mitotic activity of germline stem cells (GSCs) as well as a decrease in programmed cell death in the germarium. Our results suggest that upregulation of GSCs division is mediated by a tropism of Wolbachia for the germline stem cell niche (GSCN), the cellular microenvironment that supports GSCs.

Wolbachia are intracellular bacteria that infect invertebrates at pandemic levels, including insect vectors of devastating infectious diseases. Although Wolbachia are providing novel strategies for the control of several human pathogens, the processes underlying Wolbachia's successful propagation within and across species remain elusive. Wolbachia are mainly vertically transmitted; however, there is also evidence of extensive horizontal transmission. Here, we provide several lines of evidence supporting Wolbachia's targeting of ovarian stem cell niches-referred to as "niche tropism"-as a previously overlooked strategy for Wolbachia thriving in nature. Niche tropism is pervasive in Wolbachia infecting the Drosophila genus, and different patterns of niche tropism are evolutionarily conserved. Phylogenetic analysis, confirmed by hybrid introgression and transinfection experiments, demonstrates that bacterial factors are the major determinants of differential patterns of niche tropism. Furthermore, bacterial load is increased in germ-line cells passing through infected niches, supporting previous suggestions of a contribution of Wolbachia from stem-cell niches toward vertical transmission. These results support the role of stem-cell niches as a key component for the spreading of Wolbachia in the Drosophila genus and provide mechanistic insights into this unique tissue tropism.endosymbiont | maternal transmission | microbial tissue tropism | germline stem cell niche | somatic stem cell niche

No abstract

Wolbachia pipientis, an intracellular, alpha-proteobacterium, is commonly found in arthropods and filarial nematodes. Most infected insects are known to harbor strains of Wolbachia from supergroups A or B, whereas supergroups C and D occur only in filarial nematodes. Here, we present molecular evidence from two genes (ftsZ and 16S rDNA) that 2 Orthopterans (the bush cricket species Orocharis saltator and Hapithus agitator; Gryllidae: Eneopterinae) are infected with Wolbachia from the F supergroup. Additionally, a series of PCR tests revealed that these bush cricket specimens did not harbor nematodes, thus indicating that our positive results were not a by-product of nematodes being present in these cricket samples. Patterns of molecular variation suggest that (1) strains of F supergroup Wolbachia exhibit less genetic variation than the nematode-specific C and D supergroups but more than the A and B supergroups found in arthropods and (2) that there is no evidence of recombination within F supergroup strains. The above data support previous findings that F supergroup Wolbachia is not only harbored in both nematodes and arthropods, but that horizontal transfer has likely occurred recently between these diverse taxonomic groups (although the exact details of such horizontal transmissions remain unclear). Moreover, the limited genetic variation and lack of recombination in the F supergroup suggest that this clade of Wolbachia has radiated relatively rapidly with either (1) little time for recombination to occur or (2) selection against recombination as occurs in the mutualistic C and D strains of Wolbachia - both of which remain to be explored further.