Dietary saccharides and sweet tastants have differential effects on colonization of oocytes by endosymbionts.

bacteria are widespread, maternally transmitted endosymbionts of insects. Maintenance of sufficient titer in maternal germline cells is required for transmission efficacy. The mechanisms that regulate titer are not well understood; however, dietary sucrose was reported to elevate oocyte titer in whereas dietary yeast decreased oocyte titer. To further investigate how oocyte titer is controlled, this study analyzed the response of Mel to diets enriched in an array of natural sugars and other sweet tastants Confocal imaging of oocytes showed that food enriched in dietary galactose, lactose, maltose and trehalose elevated titer. However, oocyte titers were unaffected by exposure to the sweet tastants lactulose, erythritol, xylitol, aspartame and saccharin as compared to the control. Oocyte size was generally non-responsive to the nutrient-altered diets. Ovary size, however, was consistently smaller in response to all sugar- and sweetener-enriched diets. Furthermore, most dietary sugars administered in tandem with dietary yeast conferred complete rescue of oocyte titer suppression by yeast. All diets dually enriched in yeast and sugar also rescued yeast-associated ovary volume changes. This indicates oocyte colonization by to be a nutritionally sensitive process regulated by multiple mechanistic inputs.