| To ensure the future existence of its progeny in times of starvation or other stress, Bacillus subtilis undergoes a process called sporulation. The resultant spore is capable of surviving extreme heat, irradiation, strong acids, and desiccation. This developmental pathway begins with an asymmetric cell division giving rise to two cells of unequal size, the smaller of which is known as the forespore. The larger mother cell begins a phagocytosis-like process called engulfment, where its membranes track around the smaller forespore eventually enclosing it. The completion of engulfment serves as a morphological checkpoint to activate sigmaG, which leads to the eventual activation of sigmaK. The mother cell transcription factor sigma K is activated by SpoIVFB, an intramembrane protease that requires the sigmaG produced SpoIVB protein for its activity. My thesis research demonstrates that SpoIVFB activity, and thus sigmaK activation, are governed by two independent checkpoints: the previously identified forespore checkpoint under the control of sigmaG, and a separate checkpoint regulated by the completion of engulfment. My research demonstrates that SpoIVFB protein levels are not directly proportional to sigma K activity, supporting the hypothesis that SpoIVFB activity is regulated. |
