Engineering robust cheater prevention in bacterial differentiation via biphasic fitness

A key mechanism that multicellular organisms use to generate large groups of cells with distinct functions is differentiation, in which omni- and pluri-potent stem cells give rise to increasingly differentiated cells that lose the ability to grow and reproduce. However, the differentiation process is intrinsically prone to mutant cheater cells that never differentiate, and thus destroy cooperation by outgrowing their wild-type neighbors. A proposed mechanism to avoid these cheaters is biphasic fitness, in which a disadvantageous trait is evolutionarily stabilized by coupling to an advantageous counterpart. We have developed a synthetic culture of Escherichia coli which is capable of differentiation, both with and without biphasic coupling. Through precise, controllable evolutionary pressures and growth measurements, we analyze the benefit of this theory as applied to differentiation in a real biological system, as well as the spectrum of mutations that can or cannot be avoided through its application. This system will in turn allow us to effectively probe how large groups of cells coexist as a single unit and avoid cancerous cheaters within stem cell populations.