Figure 1.

Coordination of the sporulation response with the cell-cycle in B. subtilis.

A. In starvation, B. subtilis make cell-fate decision either to divide medially continuing vegetative growth or to divide asymmetrically committing to sporulation. The decision is based on the level of phosphorylated master regulator Spo0A (0A~P). 0A~P exceeding a threshold commit cells to sporulation whereas lower levels allows cells to continue growth. The decision must be made after the completion of DNA replication phase (yellow bar) since two complete chromosomes are needed to produce a viable spore. B–C Single cell time-lapse microscopy using a P_0A-cfp reporter for 0A~P with vertical dashed lines indicate cell divisions and yellow shaded regions indicate periods of DNA replication (detected by the presence of DnaN-YFP foci). (B) Expression level of P_0A-cfp increases in a pulsatile fashion over multiple cell-cycles in starvation media. (C) Its promoter activity (defined as production rate, an indicator of 0A~P level) also shows pulses of increasing amplitude over multiple generations. Note that DNA replication is sometimes initiated just before cell division. For each cell cycle, we can determine the time from birth to end of DNA replication (T_r) and time from birth to peak P_0A-cfp Promoter activity (T_p) represent respectively. D. Measurements of time from birth to end of DNA replication (T_r) and time from birth to peak P_0A-cfp Promoter activity (T_p) show that T_p>T_r for the vast majority of the cell-cycles implying that 0A activity peaks occurs after DNA replication is complete.