Food pH and microbial growth modulate Drosophila longevity. Sany Hoxha, Ryuichi Yamada, Christine Mak, Brooke Hunter, William Ja. Department of Metabolism & Aging, The Scripps Research Institute, Jupiter, FL.

   Dietary pH potentially influences a number of sensitive biological parameters such as microbial growth, gut homeostasis, and feeding behavior. In most Drosophila studies where dietary or drug interventions are employed, the effects of these manipulations on food pH and microorganism growth are ignored. To investigate the effect of food pH on survival, we measured fly adult lifespan on media buffered to different pH. We show that flies maintained on acidic buffered medium are long-lived compared to flies kept on buffered food of neutral or basic pH. To determine whether microorganism growth and food pH interact to affect longevity, we compared the lifespan of flies under conventional and axenic (germ-free) conditions. Under conventional conditions, microbial growth rapidly acidifies the food surface. Conversely, medium pH remains stable when flies are developed axenically and no microorganisms are present. In both conventional and axenic conditions, maximal fly lifespan is achieved on acidic medium. Moreover, flies maintained under acidic conditions consume more food, suggesting that longevity is not a result of caloric restriction. Our results show that dietary pH and microbial growth can mutually influence fly lifespan. Hence, effects that are currently attributed solely to nutritional or pharmaceutical interventions may rather be due, at least in part, to changes in medium pH, microorganism growth, and food buffering capacity.