Triggering sporulation in Bacillus subtilis with artificial two-component systems reveals the importance of proper Spo0 A activation dynamics.

Sporulation initiation in Bacillus subtilis is controlled by the phosphorylated form of the master regulator Spo0 A which controls transcription of a multitude of sporulation genes. In this study, we investigated the importance of temporal dynamics of phosphorylated Spo0 A ( Spo0 A∼ P) accumulation by rewiring the network controlling its phosphorylation. We showed that simultaneous induction of KinC, a kinase that can directly phosphorylate Spo0 A, and Spo0 A itself from separately controlled inducible promoters can efficiently trigger sporulation even under nutrient rich conditions. However, the sporulation efficiency in this artificial two-component system was significantly impaired when KinC and/or Spo0 A induction was too high. Using mathematical modelling, we showed that gradual accumulation of Spo0 A∼ P is essential for the proper temporal order of the Spo0 A regulon expression, and that reduction in sporulation efficiency results from the reversal of that order. These insights led us to identify premature repression of DivIVA as one possible explanation for the adverse effects of accelerated accumulation of Spo0 A∼ P on sporulation. Moreover, we found that positive feedback resulting from autoregulation of the native spo0A promoter leads to robust control of Spo0 A∼ P accumulation kinetics. Thus we propose that a major function of the conserved architecture of the sporulation network is controlling Spo0 A activation dynamics. [ABSTRACT FROM AUTHOR]