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キーワード:
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要旨:
Robust colony formation by Bacillus subtilis is recognized as one of the sessile,
multicellular lifestyles of this bacterium. Numerous pathways and genes are responsible for the
architecturally complex colony structure development. Cells in the biofilm colony secrete extracellular
polysaccharides (EPS) and protein components (TasA and the hydrophobin BslA) that hold them
together and provide a protective hydrophobic shield. Cells also secrete surfactin with antimicrobial
as well as surface tension reducing properties that aid cells to colonize the solid surface. Depending
on the environmental conditions, these secreted components of the colony biofilm can also promote
the flagellum-independent surface spreading of B. subtilis, called sliding. In this study, we emphasize
the influence of Ca2+ in the medium on colony expansion of B. subtilis. Interestingly, the availability of
Ca2+ has no major impact on the induction of complex colony morphology. However, in the absence
of this divalent ion, peripheral cells of the colony expand radially at later stages of development,
causing colony size to increase. We demonstrate that the secreted extracellular compounds, EPS, BslA,
and surfactin facilitate colony expansion after biofilm maturation. We propose that Ca2+ hinders
biofilm colony expansion by modifying the amphiphilic properties of surfactin.
