Quantitative effects of medium hardness and nutrient availability on the swarming motility of Serratia liquefaciens

We report the first controlled measurements of expansion rates for swarming colonies of Serratia liquefaciens under different growth conditions, combined with qualitative observations of the organization of the colony into regions of differentiated cell types. Significantly, the results reveal that swarming colonies of S. liquefaciens can have an increasing expansion rate with time. We compare and contrast the expansion rate results with predictions from a recent mathematical model which coupled key hydrodynamical and biological mechanisms. Furthermore, we investigate whether the swanning colonies grow according to a power law or exponentially (for large times), as suggested by recent theoretical results. (C) 2002 Societyfor Mathematical Biology. Published by Elsevier Science Ltd. All rights reserved.