An astounding revolution in our understanding of life on Earth has taken place since the turn of the 21st century, shaking the tree of life and our view of evolution. It involves adding new branches to the tree of life through the discovery of previously unknown groups of Archaea and Bacteria – life’s smallest yet most abundant cells. This project advances fundamental knowledge about the evolutionary patterns and functional roles of two abundant yet largely unstudied lineages of Bacteria: Patescibacteria and Chloroflexota. These cryptic microbes thrive in marine sediments, one of the largest and least understood microbial habitats, where chemical cycling occurs that affects the global ocean. This project aims to disentangle why these lineages are so prevalent, their true place in the evolutionary history of life on Earth, and how they function. The research will also shed light on why some of these lineages have resisted cultivation, which is necessary to realize their biotechnology potential. These studies will contribute thousands of high-quality single-cell genomes representing not only Patescibacteria and Chloroflexota, but also other 'microbial dark matter' lineages to the broader scientific community. Through mentored research and field work opportunities, student researchers will be trained in -omics, systematics, and biogeochemistry research techniques, leading to enhanced microbiology expertise while advancing discovery. This project leverages new single-cell a