Developmental commitment in a bacterium

We investigated developmental commitment during sporulation in Bacillus subtilis. Sporulation is initiated by nutrient limitation and involves division of the developing cell into two progeny, the forespore and the mother cell, with different fates. Differentiation becomes irreversible following division when neither the forespore nor the mother cell can resume growth when provided with nutrients. We show that commitment is governed by the transcription factors sigma(F) and sigma(E), which are activated in the forespore and the mother cell, respectively. We further show that commitment involves spollQ, which is under the control of sigma(F), and spollP, which is under the control of both sigma(F) and sigma(E). In the presence of nutrients, the forespore can exhibit rodlike, longitudinal growth when SpollQ and SpollP are absent, whereas the mother cell can do so when SpollP alone is absent. Thus, developmental commitment of this single-celled organism, like that of the cells of complex, multicellular organisms, ensures that differentiation is maintained despite changes in the extracellular milieu.