Endosymbiosis involves one organism dwelling inside another. One of the most successful endosymbionts is Wolbachia pipientis, a bacterium carried by about half of insect species, including the model insect Drosophila, the fruit fly. Like many other endosymbionts, Wolbachia are transmitted by females to their offspring during egg development. The overall goal of this project is to elucidate the cellular and molecular mechanisms that facilitate Wolbachia maternal transmission. This will include creating a mathematical model of fruit fly egg-cell colonization by Wolbachia, and using the model to test predictions about the factors governing Wolbachia density within developing eggs. Modeling intracellular endosymbiont dynamics is virtually unprecedented, thus this work will provide new insights as well as a valuable analytical tool. In addition, the nutritional signals that regulate host transport and thus Wolbachia distribution within fruit fly eggs will be elucidated. As cellular transport processes are also crucial for establishing the insect body plan, these analyses will inform Wolbachia transmission and insect development as an integrated process. This will link concepts that have been regarded as mechanistically separate. The research will be performed at a majority-minority, Hispanic-serving institution and the nation's largest producer of STEM minority undergraduate degrees. Trainees carrying out this project will also create essays that explain research practices and benefits. These essays will be shared in a web-based outreach forum to enrich public understanding of science.Wolbachia pipientis is among the most widespread of endosymbionts. This maternally transmitted bacterium has a streamlined genome and a facultative intracellular lifestyle. The high prevalence of Wolbachia in insect populations requires robust transmission-enhancing strategies. The overall goal of this project is to apply chemical, genetic and nutritional approaches to define the impacts of host diet and nutrient-responsive signaling on Wolbachia and germline determinant localization in oogenesis. The first aim involves defining how Wolbachia colonize Drosophila maternal germline cells as an integrated physiological process. Though Wolbachia titer in developing oocytes is responsive to host manipulation, the relative contributions of host and symbiont to titer regulation is unknown. To address this issue, Wolbachia life cycle and invasion dynamics, as well as host germline development rates will be assessed cytologically and used to estimate the parameters of a mathematical model. The model will be the first to test for conservation of Wolbachia colonization mechanisms across host-strain combinations, as well as in response to nutrient-sensitive signaling cues. The second aim is to elucidate how strategic Wolbachia localization is regulated during oogenesis. In D. melanogaster, microtubule-based motor proteins concentrate Wolbachia and posterior/germline determinants at the oocyte posterior cortex, thus pre-positioning Wolbachia at the germ cell formation site. The impact of nutritional signaling on this process will be studied using genetic approaches. Taken together, this work will comprehensively inform the cellular basis for transmission of this endosymbiont.