Swarmer cells of Proteus mirabilis migrate faster than swimmer cells in viscous environments

Abstract

It has been suggested that swarming, a type of surface motility that allows rapid migration, is involved in urinary tract colonization. During swarming, cells of P. mirabilis undergo a morphological change from ~5 μm long rods with 5–15 flagella to ~10–50 μm long rods with 50 to more than 100 flagella. Prior work has shown that increasing the number of flagella on a cell does not yield the expected increase in torque – i.e., a four‐fold increase in the number of flagella yields less than a two‐fold increase in torque. This result suggests that the dense flagellation of swarmer cells should not convey a motility advantage. However, mutant cells of Bacillus pseudiformis that express an increased number of flagella do swim faster than their wild‐type counterparts in viscous solutions, and it has been proposed that this increase in speed is due to altered flagellar bundling. We are examining whether this phenomenon also occurs with the different morphological forms of P. mirabilis. We have found that swarmer cells of wild‐type P. mirabilis are significantly faster (P<0.001) than all other cell types in media with a viscosity of 9 – 830 cP. In media with a viscosity of 8340 cP, swarmer cells are motile while all other cell types are amotile. These results suggest a possible role for the swarm cell morphology: allowing migration through viscous mucosal layers during infection.