is usually a monoflagellated bacterium that can use its single polar

is usually a monoflagellated bacterium that can use its single polar flagellum to swim through liquids and move collectively over semisolid surfaces a behavior called swarming. bacterial adaptations to surface motility such as hyperswarming requires a collective behavior approach. Introduction is an opportunistic human pathogen and an environmental microbe that is capable of living in a variety of environments. This versatile microbe has several types of motility including twitching swimming and swarming motility. Swimming in is usually mediated by a single polar flagellum1. Its flagellar motor can rotate in two directions clockwise or counterclockwise resulting in either forward or backward propulsion in aqueous environments2. Swarming is usually a collective form of surface motility where a dense colony of bacteria migrates on a semi-solid surface such as an agar gel3 4 MK-4305 (Suvorexant) Like swimming swarming motility requires flagellar motility3 but in addition it requires the production and secretion of rhamnolipid surfactants thought to reduce friction between bacteria and the surface5-11. Swarming occurs in many species of bacteria12. The fact that this same flagellar system that drives swarming also enables to swim in liquids raises the question of whether swimming and swarming are distinct phenomena13. Here we present evidence that these are indeed distinct phenomena at least in colony covers about ? of the agar plate making characteristic branched patterns14. In MK-4305 (Suvorexant) MK-4305 (Suvorexant) contrast colonies of hyperswarmers can cover the whole agar Rabbit Polyclonal to CRABP2. plate and show no branching patterns (Fig. 1B). Hyperswarmers are also poor biofilm formers compared to wild-type. This supports the presence of an antagonism between biofilm formation and motility which may affect the pathogenicity of and may eventually lead to new therapies against biofilm formation13. Physique 1 Motility patterns of non-flagellated (?in liquid by measuring swimming speeds MK-4305 (Suvorexant) using a single-cell tracking method and quantitative image analysis. Counter-intuitively we observed that hyperswarmers do not swim faster than wild-type. Having multiple flagella does however increase the variability in swimming speed of single cells which become much more likely to alter their velocity after a turn and to make wider turns than the wild-type. We also performed single-cell tracking through soft agar. We observed that wild-type swim slightly faster than hyperswarmers in this environment. However hyperswarmers diffuse much faster than wild-type. A mathematical model with adjustable turning angle explains how a wider turning angle distribution can lead to a faster spreading. These contrasting observations support that in order to understand the evolutionary adaptations to swarming such as hyperswarming one must study bacterial motility from a collective behavior perspective. Results and discussion Hyperswarmers move faster through and on agar gels Swarming and swimming through agar in and its hyperswarmer mutants has only been compared through end-point measurements14. Here we measured the expansion velocity by tracking the colony edge over time. We first quantified swimming in the classical microbiology swimming assay. This assay consists of observing the spreading of a colony as it swims through soft agar prepared at a concentration of 0.3% (w/v). In agreement with previous measurements14 both hyperswarmer clones spread significantly faster than wild-type (Fig. 2). Next we tracked the expansion of swarming colonies (Fig. 3A B). The total MK-4305 (Suvorexant) area of the colony (Fig. 3C) and the speed of the advancing edge (tracked by following the tip of the tendrils for wild-type or the protrusions for the hyperswarmers Fig. 3D) reveal that hyperswarmers are faster than wild-type (Fig. 2D p<0.001 by Kruskal-Wallis test). The typical swimming velocity (1 mm/h) does not match the typical swarming velocity (3 mm/h) reinforcing that these two motility modes differ mechanistically. Physique 2 Hyperswarmers spread faster than wild-type when swimming through 0.3% (w/v) agar the classical microbiology assay to assess motility. Plot shows the radius of expanding swimming colonies as a function of time. Physique 3 Hyperswarmers spread faster than wild-type over soft surfaces prepared at 0.5% (w/v) agar (swarming.