[Structural organization and distribution of symbiotic bacteria Wolbachia in early embryos and ovaries of Drosophila melanogaster and D. simulans].

Electron microscopic and morphometric analyses of Wolbachia distribution in early embryos of Drosophila flies have demonstrated that the number of bacteria in the embryo remains constant from fertilization to blastoderm, and that afterwards the symbionts could be observed only in the polar cells. Each bacterium has a three-layer envelope, makes contacts with microtubules and moves through the cytoplasm following the actively dividing nuclei. It has been found for the first time that Wolbachia could produce secretory vacuoles in the cytoplasm of early embryos. The relative volume of Wolbachia was five times as much in the embryos of Drosophila simulans as in those of D. melanogaster (Canton S), while the survival rate of D. simulans was half as much as that of D. melanogaster. It was shown that Wolbachia could form spore-like structures in D. simulans embryos. Ultrastructural investigations of Drosophila ovaries suggest that the bacteria may be present in all ovariol cells, including the oocyte, within whose cytoplasm they are delivered to the host. The highest number of symbionts was observed in germarium cells. In ovariol cells, the bacteria gradually decrease in number as oogenesis progresses. It has been determined for the first time that the symbionts are located closely to membranes of rough endoplasmatic reticulum in follicular and nurse cells of D. melanogaster. The data obtained suggest that Wolbachia may be involved in the regulation of oocyte maturation.