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Mechanisms Controlling Wolbachia Titer and Transmission


Wolbachia are gram-negative, obligate, intracellular bacteria infecting a majority of insect species and filarial nematodes. In both insects and nematodes Wolbachia are primarily transmitted through the female germ line. Wolbachia carried by filarial nematodes are the cause of the neglected diseases African river blindness and lymphatic filariasis afflicting millions worldwide. In order to combat these diseases, we created a Wolbachia-infected Drosophila cell line that enabled high throughput screening for novel potent anti-Wolbachia compounds. Of the 36,231 compounds screened in house, 8 compounds dramatically reduced Wolbachia titer both in the cell and nematode based screen. Significantly, we discovered that the albendazole metabolite, albendazole sulfone, reduces Wolbachia titer in Drosophila melanogaster and the filarial nematode Brugia malayi perhaps by directly targeting Wolbachia FtsZ. Using the Wolbachia-infected cell line, we discovered that in addition to vertical germ line transmission, Wolbachia are efficiently transmitted horizontally via cell-to-cell transmission. We show that horizontal transfer is independent of cell-to-cell contact, can efficiently take place within hours, and uses both host cell phagocytic and clathrin/dynamin-dependent endocytic machinery. Modifications to our high-throughput screen in combination with genome-wide RNA interference (RNAi) identified host factors that influence Wolbachia titer. When these host factors were tested in Drosophila melanogaster in vivo we found that maintenance of Wolbachia titer relies on an intact host Endoplasmic Reticulum (ER) associated degradation (ERAD) system. These data, in combination with electron microscopy studies, demonstrated that Wolbachia is intimately associated with the host ER and suggested a previously unsuspected mechanism for the potent ability of Wolbachia to prevent RNA virus replication. To examine the impact of nutritional on Wolbachia titer, Drosophila were fed sucrose- and yeast-enriched diets. These conditions resulted in increased and decreased Wolbachia titer in Drosophila oogenesis, respectively, and that somatic TOR and insulin signaling mediate the response of the yeast-enriched diet on Wolbachia. Taken together, these studies provide initial insights into the molecular and cellular interactions between Wolbachia and its insect and nematode hosts.

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