Thinking about Bacillus subtilis as a multicellular organism

Abstract

Initial attempts to use colony morphogenesis as a tool to investigate bacterial multicellularity were limited by the fact that laboratory strains often have lost many of their developmental properties. Recent advances in elucidating the molecular mechanisms underlying colony morphogenesis have been made possible through the use of undomesticated strains. In particular, Bacillus subtilis has proven to be a remarkable model system to study colony morphogenesis because of its well-characterized developmental features. Genetic screens that analyze mutants defective in colony morphology have led to the discovery of an intricate regulatory network that controls the production of an extracellular matrix. This matrix is essential for the development of complex colony architecture characterized by aerial projections that serve as preferential sites for sporulation. While much progress has been made, the challenge for future studies will be to determine the underlying mechanisms that regulate development such that differentiation occurs in a spatially and temporally organized manner.

Figure 1

Color plate containing the eleven figures accompanying Koch’s (figs 1–7) and Cohn’s (figs 8–11) papers from 1877 [3,4]. Original volume provided courtesy of the Farlow Botanical Library, Harvard University.

Figure 2

Examples of the differences in colony morphology between undomesticated and domesticated strains of three bacterial species.

Figure 3

Time course of B. subtilis colony morphogenesis.

Figure 4

Diagram outlining the genetic circuitry regulating the transition between motile cells and matrix-producing cells.