Additional Study Information: A complication that can occur after liver transplant (LT) is rejection, in which the patient's immune system damages the transplanted liver. Tacrolimus is the primary medication used in most patients to suppress the immune system and prevent this complication after LT. The main purpose of this study is to determine if bacteria in the intestine (gut microbiome) may affect how tacrolimus is processed by the body. If you have any questions regarding this study, please contact the Transplant Clinical Research Center (TCRC)