Phenotyping single-cell motility of single gene variants during fruiting body formation in Myxococcus xanthus

The soil dwelling bacterium Myxococcus xanthus displays a complex set of collective behaviors, such as swarming, predation, and, upon starvation, fruiting body formation. During fruiting body formation, cells aggregate into three-dimensional mounds composed of approximately 10⁵ cells. This process allows a subset of cells to sporulate and become starvation-resistant. Mutants show a wide variety of aggregation phenotypes, with variations in aggregation timing, size, number, and mound characteristics. We hypothesize that this aggregation phenotype diversity is driven, in part, by changes in single cell motility phenotype. M. xanthus move by gliding along their long axis and periodically reverse their direction of motion by switching their leading and lagging poles. Here, we utilize time-lapse microscopy to characterize aggregation phenotypes and single cell tracking of fluorescently labeled cells to quantify cell motility parameters including cell speed and reversal frequency, and show how subtle variations in single cell motility drive differences in aggregation phenotype. We demonstrate that single cell dynamics play an important role in shaping emergent collective behavior.