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Front. Microbiol. | doi: 10.3389/fmicb.2019.00842

A sequence of developmental events occurs underneath growing Bacillus subtilis pellicles

  • 1School of Engineering and Applied Sciences, Harvard University, United States
  • 2Weizmann Institute of Science, Israel

Biofilms are structured communities of bacteria that exhibit complex spatio-temporal dynamics. In liquid media, Bacillus subtilis produces an opaque floating biofilm, or a pellicle. Biofilms are generally associated with an interface, but the ability of Bacillus subtilis to swim means the bacteria are additionally able to reside within the liquid phase. However, due to imaging complications associated with the opacity of pellicles, the extent to which bacteria coexist within the liquid bulk as well as their behavior in the liquid is not well studied. We therefore develop a high-throughput imaging system to image underneath developing pellicles. Here we report a well-defined sequence of developmental events that occurs underneath a growing pellicle. Comparison with bacteria deficient in swimming and chemotaxis suggest that these properties enable collective bacterial swimming within the liquid phase which facilitate faster surface colonization. Furthermore, comparison to bacteria deficient in exopolymeric substances (EPS) suggest that the lack of a surface pellicle prevents further developmental steps from occurring within the liquid phase. Our results reveal a sequence of developmental events during pellicle growth, encompassing adhesion, conversion, growth, maturity, and detachment on the interface, which are synchronized with the bacteria in the liquid bulk increasing in density until the formation of a mature surface pellicle, after which the density of bacteria in the liquid drops.

Keywords: Pellicles, Biofilms and colonies, development, collective behavior and dynamics, Flagellar motility

Received: 15 Jan 2019; Accepted: 02 Apr 2019.

Edited by:

Eva Ortega-Retuerta, UMR7621 Laboratoire d'océanographie microbienne (LOMIC), France

Reviewed by:

Cristina Madrid, University of Barcelona, Spain
Nay El Khoury, INRA Centre Jouy-en-Josas, France  

Copyright: © 2019 Lee, Rosenberg and Rubinstein. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Shmuel M. Rubinstein, School of Engineering and Applied Sciences, Harvard University, Cambridge, 02138, Massachusetts, United States, shmuel@seas.harvard.edu