Characterization of Swarmer Cell Differentiation in Proteus mirabilis

Some bacteria translocate across quasi-solid surfaces via a multicellular type of motility called swarming. Swarming is performed by highly elongated and hyperflagellated differentiated swarmer cells. It is known that swarmer cell differentiation occurs upon surface contact. However, cellular and environmental factors affecting swarmer cell differentiation remain poorly understood. Here, we studied swarmer cell differentiation in Proteus mirabilis. We found that swarmer differentiation occurs abruptly at a critical cell density. In order to understand this tight regulation, we have analyzed the gene regulatory network controlling the expression of the master regulator flhDC. Interestingly, our single-cell-level experiments show that both initiation of and commitment to differentiation are stochastic. Our efforts to mechanistically bridge this single-cell-level stochasticity in differentiation and its population-level tight regulation will also be discussed.