title: Water surface tension modulates the swarming mechanics of Bacillus subtilis.
abstract: Many Bacillus subtilis strains swarm, often forming colonies with tendrils on agar medium. It is known that B. subtilis swarming requires flagella and a biosurfactant, surfactin. In this study, we find that water surface tension plays a role in swarming dynamics. B. subtilis colonies were found to contain water, and when a low amount of surfactin is produced, the water surface tension of the colony restricts expansion, causing bacterial density to rise. The increased density induces a quorum sensing response that leads to heightened production of surfactin, which then weakens water surface tension to allow colony expansion. When the barrier formed by water surface tension is breached at a specific location, a stream of bacteria swarms out of the colony to form a tendril. If a B. subtilis strain produces surfactin at levels that can substantially weaken the overall water surface tension of the colony, water floods the agar surface in a thin layer, within which bacteria swarm and migrate rapidly. This study sheds light on the role of water surface tension in regulating B. subtilis swarming, and provides insight into the mechanisms underlying swarming initiation and tendril formation.
authors.affiliation: Department of Microbiology and Immunology, Chang Gung University Taoyuan, Taiwan ; Research Center for Bacterial Pathogenesis, Chang Gung University Taoyuan, Taiwan.
authors.forename: Wan-Ju
authors.initials: WJ
authors.lastname: Ke
authors.affiliation: Graduate School of Biotechnology and Bioengineering, Yuan Ze University Taoyuan, Taiwan.
authors.forename: Yi-Huang
authors.initials: YH
authors.lastname: Hsueh
authors.affiliation: Department of Microbiology and Immunology, Chang Gung University Taoyuan, Taiwan.
authors.forename: Yu-Chieh
authors.initials: YC
authors.lastname: Cheng
authors.affiliation: Department of Medical Biotechnology and Laboratory Science Proteomic Center, College of Medicine, Chang Gung University Taoyuan, Taiwan.
authors.forename: Chih-Ching
authors.initials: CC
authors.lastname: Wu
authors.affiliation: Department of Microbiology and Immunology, Chang Gung University Taoyuan, Taiwan ; Department of Medical Research and Development, Chang Gung Memorial Hospital Chiayi Branch Chiayi, Taiwan.
authors.forename: Shih-Tung
authors.initials: ST
authors.lastname: Liu
keywords: Bacillus subtilis; quorum sensing; surfactin; swarming; water surface tension