Sensing and Switching in Bacterial Sporulation

Spore formation in the rod-shaped bacterium Bacillus subtilis and its relatives is an extreme response to starvation. It is characterised by an asymmetric division, giving rise to cells of unequal size which follow different programmes of gene expression orchestrated by compartment-specific RNA polymerase sigma factors. The larger mother cell next engulfs the smaller forespore and nurtures the development of the latter into a resistant spore. The spore is released upon programmed cell death of the mother cell, and can lie dormant indefinitely, germinating when nutrients once again become available.In this talk, proteins sensing and responding to starvation signals will be introduced and the structural basis of their action will be described. This will be followed by discussion of a system of proteins that leads to the activation of the first compartment-specific sigma factor, sigmaF, and the establishment of alternate cell fates. This includes regulation by protein phosphorylation and the unexpected discovery of a regulatory mechanism that is common to a widespread family of protein phosphatases and to proteasomal proteases.