The data from each gel was corrected using the calibration curve specific to that gel. increased flagellum density produced an increase in cell velocity. Our results establish a relationship between flagellum density and cell motility in viscous environments that may be relevant to its adaptation during the contamination of mammalian urinary tracts and movement in contact with indwelling catheters. INTRODUCTION is usually a Gram-negative rod-shaped gammaproteobacterium that is commonly associated with urinary tract infections (1) and the biofouling of catheters (2C4). may also be present in the human gut microflora (5) and is correlated with the incidence of colitis Aprocitentan (6, 7). Broth-grown vegetative cells of are characteristically 2 m long and have a peritrichous distribution of 4 to 10 flagella. The flagella form a bundle that performs work on the surrounding fluid and propels cells forward via a mechanism that is similar to the motility system of (8, 9). Broth-grown vegetative cells of in contact with the surface of agar gels infused with nutrients switch their morphology, become swarmers, and colonize the surface by coordinating the movement of large groups of cells (i.e., swarming) (observe Fig. 1A). swarm colonies exhibit a terraced pattern of concentric rings (observe Fig. S1 in the supplemental material) (10). These rings are produced by alternating phases of consolidation, during which the colony does not expand and cells are dedifferentiated into a vegetative cell-like morphology, and swarming, during which cells are motile and differentiated (11). Motility occurs predominantly at the swarm front and decreases with increasing distance from the front; cells near the center of the swarm are nonmotile. Swarming has several characteristics, including the following: (i) the inhibition of cell division to produce long (10- to 70-m) multinucleate cells, (ii) an increase in the surface density of flagella, (iii) the secretion of biomolecules that alter the surface tension of water and extract a thin layer of fluid from your gel, Aprocitentan and (iv) the movement of cells in close physical proximity within the thin layer of fluid (11C14). In this work, we investigated whether cell length and FCRL5 flagellum density confer an advantage for swarm cell motility. Open in a separate windows Fig 1 (A) A cartoon of a current model for the swarming life cycle (adapted from (12) with permission of the publisher). Vegetative cells in contact with an agar surface morphologically differentiate into swarm cells, assemble into multicellular rafts, and move across the surface cooperatively. Swarm cells dedifferentiate into consolidated cells. (B) Bright-field microscopy images of the leading edge of a swarm colony during migration (left panel) and consolidation (right panel). Bacteria live at a low Reynold’s number, where viscous causes play a central role in motility (15), and flagella enable cells to move through fluids at a relatively high energetic cost to the cell (2% of the total energy of the cell) (16). The motility of vegetative bacterial cells increases as the dynamic viscosity of the surrounding fluid increases; above a threshold that varies for different species of bacteria, cell velocity decreases rapidly (17C23). The viscosity required for total inhibition of motility varies widely, with values ranging from 0.06 to 1 1 Pa s (17). The relationship between velocity and viscosity can be explained in part by treating the liquid as a loose, quasirigid network that increases the resistance to cell movement in the direction normal to the cell body (24). vegetative cell motility in viscous liquids has been investigated (25); however, little is known about the effect of increasing viscosity around the motility of swarm cells of bacteria, including cells. We tested the hypothesis that these phenotypes convey an advantage for the movement of swarm Aprocitentan cells through viscous fluids, including the extracellular environment found in swarms (26, 27). We isolated and characterized populations of cells with the following combinations of cell length and flagellum density: (i) short cells with a normal density of flagella (vegetative cells), (ii) long cells with a normal density of flagella (elongated vegetative cells), (iii) long cells with a high density of flagella (swarm cells), and (iv) short cells with a high density of flagella (consolidated cells). We quantitatively measured the motility of individual cells of each of these groups in liquids Aprocitentan that had a range of viscosities. These experiments enabled us to determine the functions of cell length and flagellum Aprocitentan density in bacterial cell motility in viscous environments. Additionally, we examined the effect of overexpressing genes during swarming contributes.