AUTHOR=Ke Wan-Ju , Hsueh Yi-Huang , Cheng Yu-Chieh , Wu Chih-Ching , Liu Shih-Tung 

TITLE=Water surface tension modulates the swarming mechanics of Bacillus subtilis

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.01017

DOI=10.3389/fmicb.2015.01017

ISSN=1664-302X

ABSTRACT=<p>Many <italic>Bacillus subtilis</italic> strains swarm, often forming colonies with tendrils on agar medium. It is known that <italic>B. subtilis</italic> swarming requires flagella and a biosurfactant, surfactin. In this study, we find that water surface tension plays a role in swarming dynamics. <italic>B. subtilis</italic> 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 <italic>B. subtilis</italic> 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 <italic>B. subtilis</italic> swarming, and provides insight into the mechanisms underlying swarming initiation and tendril formation.</p>