Self-driven phase transitions in living matter

The soil dwelling bacterium {\it Myxococcus xanthus} is an amazing organism that uses collective motility to hunt in giant packs when near prey and to form beautiful and protective macroscopic structures comprising millions of cells when food is scarce. I will present an overview of how these cells move and how they regulate that motion to produce different phases of collective behavior. Inspired by recent work on of active matter, I will discuss experiments that reveal how these cells generate nematic order and how they actively tune the P\'eclet number of the population to drive a phase transition from a gas-like flocking state to an aggregated liquid-droplet state during starvation