Editors' ChoiceMicrobiology

A Spore’s Lifeline

Science Signaling  28 Apr 2009:
Vol. 2, Issue 68, pp. ec144
DOI: 10.1126/scisignal.268ec144

Bacterial sporulation begins with an asymmetric cell division that produces a larger mother cell and a smaller forespore that is engulfed by the mother cell; subsequent intercellular signaling events lead to the maturation of the forespore and disintegration of the mother cell to form the dormant endospore. Activity of the σF transcription factor in the forespore is required for expression of spoIIQ, which encodes a transmembrane protein, in the forespore and for activation of σE in the mother cell, which promotes transcription of the spoIIA operon in the mother cell. Eight spoIIA-encoded proteins from the mother cell (SpoIIIAA–SpoIIIAH) and SpoIIQ from the forespore form a channel-like complex required for activation of σG in the forespore. Camp and Losick found that the extracellular domain of SpoIIQ was required for assembly, proper localization, and function of the complex as assayed by the ability of channels incorporating various mutant components to support sporulation. The presence and proper assembly of the complex were required for a previously unrecognized late phase of σF activity in the forespore and for the ability of T7 RNA polymerase heterologously expressed in the forespore to drive production of β-galactosidase from a reporter construct during late, but not early, stages of sporulation. The inability of T7 RNA polymerase to drive production of β-galactosidase during late stages of sporulation in the absence of functional channels suggested that the forespore lost its ability to support its own biosynthetic activities as sporulation progressed. The authors proposed that the channel functioned similarly to a eukaryotic gap junction in that it enabled transport of small molecules, such as amino acids or nucleotides, required for continued macromolecular synthesis into the forespore from the mother cell. Although these observations do not preclude the passage of a specific σG regulatory factor from the mother cell into the forespore, they suggest that signaling between the two cells may depend on nonselective transfer of molecules from the mother cell to support development of the forespore.

A. H. Camp, R. Losick, A feeding tube model for activation of a cell-specific transcription factor during sporulation in Bacillus subtilis. Genes Dev. 23, 1014–1024 (2009). [Abstract] [Full Text]