Fruiting body formation by <i>Bacillus</i> <i>subtilis</i>

TLDR

Spore formation in *Bacillus subtilis* has been studied mainly at the single‑cell level, yet recent work with natural isolates shows spatial organization in biofilms and suggests other microbial differentiation processes may also exhibit multicellular organization. Fruiting body formation depends on early sporulation regulatory genes and on genes required for exopolysaccharide and surfactin production. In biofilms, motile cells form aligned chains that develop into aerial fruiting bodies that preferentially support sporulation; this robust aerial structure is present in natural isolates but absent in laboratory strains, indicating loss of multicellularity during domestication.

Abstract

Spore formation by the bacterium Bacillus subtilis has long been studied as a model for cellular differentiation, but predominantly as a single cell. When analyzed within the context of highly structured, surface-associated communities (biofilms), spore formation was discovered to have heretofore unsuspected spatial organization. Initially, motile cells differentiated into aligned chains of attached cells that eventually produced aerial structures, or fruiting bodies, that served as preferential sites for sporulation. Fruiting body formation depended on regulatory genes required early in sporulation and on genes evidently needed for exopolysaccharide and surfactin production. The formation of aerial structures was robust in natural isolates but not in laboratory strains, an indication that multicellularity has been lost during domestication of B. subtilis. Other microbial differentiation processes long thought to involve only single cells could display the spatial organization characteristic of multicellular organisms when studied with recent natural isolates.