This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Dietary oxalate plays a critical role in kidney stone formation. Preliminary evidence suggests that degradation of dietary oxalate by the gut organism, Oxalobacter formigenes, may limit the amount of oxalate absorbed and excreted in urine. To identify the role of Oxalobacter formigenes we will examine the response of normal subjects, who are either colonized or not colonized with the bacterium, to changes in dietary oxalate and calcium. These studies will be performed using the metabolic kitchen of the GCRC to prepare diets that are controlled in their contents of oxalate, calcium and other nutrients. Subjects will consume diets with 3 levels of oxalate and 3 levels of calcium. Each diet will be consumed for 7 days and subjects will collect all urine and feces passed for analysis. These samples will be analyzed for Oxalobacter, oxalate and calcium. The results will illustrate the potential importance of Oxalobacter colonization in kidney stone formation and identify how dietary oxalate and calcium regulate colonization levels of Oxalobacter in the gut.