title: Single-cell analysis in situ in a Bacillus subtilis swarming community identifies distinct spatially separated subpopulations differentially expressing hag (flagellin), including specialized swarmers.
abstract: The non-domesticated Bacillus subtilis strain 3610 displays, over a wide range of humidity, hyper-branched, dendritic, swarming-like migration on a minimal agar medium. At high (70 %) humidity, the laboratory strain 168 sfp+ (producing surfactin) behaves very similarly, although this strain carries a frameshift mutation in swrA, which another group has shown under their conditions (which include low humidity) is essential for swarming. We reconcile these different results by demonstrating that, while swrA is essential for dendritic migration at low humidity (30-40 %), it is dispensable at high humidity. Dendritic migration (flagella- and surfactin-dependent) of strains 168 sfp+ swrA and 3610 involves elongation of dendrites for several hours as a monolayer of cells in a thin fluid film. This enabled us to determine in situ the spatiotemporal pattern of expression of some key players in migration as dendrites develop, using gfp transcriptional fusions for hag (encoding flagellin), comA (regulation of surfactin synthesis) as well as eps (exopolysaccharide synthesis). Quantitative (single-cell) analysis of hag expression in situ revealed three spatially separated subpopulations or cell types: (i) networks of chains arising early in the mother colony (MC), expressing eps but not hag; (ii) largely immobile cells in dendrite stems expressing intermediate levels of hag; and (iii) a subpopulation of cells with several distinctive features, including very low comA expression but hyper-expression of hag (and flagella). These specialized cells emerge from the MC to spearhead the terminal 1 mm of dendrite tips as swirling and streaming packs, a major characteristic of swarming migration. We discuss a model for this swarming process, emphasizing the importance of population density and of the complementary roles of packs of swarmers driving dendrite extension, while non-mobile cells in the stems extend dendrites by multiplication.
authors: Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
authors: Kassem
authors: K
authors: Hamze
authors: Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
authors: Sabine
authors: S
authors: Autret
authors: Medical University of Gdansk, Debinki 1, 80-211, Department of Medical Biotechnology, Intercollegiate Faculty of Biotechnology, Gdansk, Poland.|Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
authors: Krzysztof
authors: K
authors: Hinc
authors: CNRS UPR9273, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France.
authors: Soumaya
authors: S
authors: Laalami
authors: Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
authors: Daria
authors: D
authors: Julkowska
authors: INRA, UMR1319 MICALIS, Jouy-en-Josas, France.
authors: Romain
authors: R
authors: Briandet
authors: INRA, UMR1319 MICALIS, Jouy-en-Josas, France.
authors: Margareth
authors: M
authors: Renault
authors: Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
authors: Cédric
authors: C
authors: Absalon
authors: Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
authors: I Barry
authors: IB
authors: Holland
authors: CNRS UPR9273, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France.
authors: Harald
authors: H
authors: Putzer
authors: Université Paris-Sud, Institut de Génétique et Microbiologie, UMR CNRS 8621, Bât. 409, 91405 Orsay Cedex, France.
authors: Simone J
authors: SJ
authors: Séror