Bacteria rst became prominent as model organisms for studies of fundamental aspects of aging and age-related diseases during the last several decades of the twentieth century. During that era data from bacteria seemed to reinforce the popular (conventional) mitochondrial theory of aging featuring oxidative stress acting as a mutagen and directly driving the aging process. For example, data from bacteria showed that reactive oxygen species (ROS) could chemically modify bacterial DNA and cause mutations-a nding consistent with a direct linkage between ROS, mutations, and aging.