Where's Wolbachia?

Wolbachia Wolbachia pipientis is a maternally inherited symbiotic bacteria that is widespread among most insects including laboratory stocks of Drosophila melanogaster, as well as filarial nematodes and crustaceans. Wolbachia belong to the Richettsial family responsible for the deadly human diseases such as typhus, Rocky Mountain spotted fever, and Q fever, but themselves are not involved in any known human diseases. Wolbachia are best known for their ability to induce reproductive alterations in hosts such as male killing, feminization, parthenogenesis, and cytoplasmic incompatibility, all of which result in increased number of infected female offspring and thereby helping vertical transfer of Wolbachia. These reproductive alterations may promote speciation in extreme cases. Because of these intriguing properties, Wolbachia have been extensively studied for entomology, agriculture and evolution.

Despite Wolbachia’s unique role in host reproduction and physiology, their underlying cellular mechanisms are yet to be addressed. Studies with electron microscopy have revealed that Wolbachia bacteria are strictly present in vesicular structures in the cytoplasm of host cells. These Wolbachia vesicles are attached to astral microtubules near centrosomes by short electron-dense bridges, and their centrosomal localization is dependent on microtubules but not actin. Wolbachia bacteria are enclosed within three layers of membranes: the outer layer is host origin and two inner layers are bacterial cell wall and bacterial plasma membrane. Since parasitic bacteria and enveloped mammalian viruses often utilize a variety of subcellular organelles such as endoplasmic reticulum and Golgi apparatus during their life cycles, Wolbachia may also be present in a host organelle that can aid the replication and propagation of Wolbachia. Identification of this host organelle is critical for understanding the Wolbachia‘s ability in changing host physiology.

This paper reports that Wolbachia reside in a group of Golgi-related vesicles. This raises an interesting possibility that Wolbachia may mark the unique group of Golgi vesicles linked to membrane biogenesis. The additional finding that localization of Wolbachia vesicles is regulated by genes involved in cell/tissue polarity also provided a surprising new potential activity for these polarity genes in Golgi localization.

 

Wolbachia Bacteria Reside in Host Golgi-Related Vesicles Whose Position Is Regulated by Polarity Proteins. (2011) PLoS ONE 6(7): e22703. doi:10.1371/journal.pone.0022703
Wolbachia pipientis are intracellular symbiotic bacteria extremely common in various organisms including Drosophila melanogaster, and are known for their ability to induce changes in host reproduction. These bacteria are present in astral microtubule-associated vesicular structures in host cytoplasm, but little is known about the identity of these vesicles. We report here that Wolbachia are restricted only to a group of Golgi-related vesicles concentrated near the site of membrane biogenesis and minus-ends of microtubules. The Wolbachia vesicles were significantly mislocalized in mutant embryos defective in cell/planar polarity genes suggesting that cell/tissue polarity genes are required for apical localization of these Golgi-related vesicles. Furthermore, two of the polarity proteins, Van Gogh/Strabismus and Scribble, appeared to be present in these Golgi-related vesicles. Thus, establishment of polarity may be closely linked to the precise insertion of Golgi vesicles into the new membrane addition site.

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