Summary Despite the enormous literature of studies involving both germ-free and conventional mice, it is still largely unclear about the lipid profile, lipoprotein distribution and apolipoprotein content as analyzed by FPLC, and the difference in intestinal lipid absorption efficiency between germ-free animals and conventional animals. The goal of this supplemental grant is to obtain these data through a collaboration among the germ-free core, microbiome core and the phenotyping core at the University of Michigan and the lipid and the lipoprotein Core at the University of Cincinnati. This collaboration will yield data complementary to the current collaboration of the microbiome project conducted by Michigan, Vanderbilt, and UC Davis. The proposed research is highly feasible because there is no need to transfer live mice between these two centers. Instead, we will take advantage of the resources and expertise of the two centers. We have proposed the following two specific aims to achieve the goal. In Aim 1, we will determine the lipid profile and apolipoprotein composition in both male and female germ-free mice that will be fed a semi-purified diet fortified with low fat diet or high fat diet. Half of the animals will be colonized while the other half will remain germ free. In Aim 2, we will determine the difference in intestinal fat absorption between the male and female germ-free and conventional mice using a well-established non-invasive method. The proposed research is important because the completion of the proposed studies will tell us how chronic feeding of semi-purified high- and low-fat diets influence the changes in the lipid profile, lipoprotein and apolipoprotein composition. Without this information, it is difficult to understand how microbiome affects lipid and lipoprotein metabolism, as well as cardiovascular disease, diabetes, and obesity. Additionally, the completion of the non-invasive fat absorption studies will support our hypothesis that the germ-free animals are not absorbing lipid as well as the conventional animals. This is based on our antibiotics study published in Gastroenterology. If indeed this is the case, future experiments will be conducted to define the link between microbiome and intestinal lipid transport as chylomicrons. We foresee numerous collaborations between our two MMPCs.