A mathematical kinetic model of memory in Bacillus subtilis spore germination

Dormant Bacillus subtilis spores germinate through interaction of germinants with germination receptors (GRs). Subsequently, the activated GR signal is transduced to SpoVA proteins that constitute transport channels. SpoVA channel opening then leads to calcium dipicolinic acid (CaDPA) release and completion of spore germination. Spores are known to exhibit memory in germination, as spores given an initial short germinant pulse respond more readily to a second pulse. We have developed a mathematical model to identify a minimal reconstructed molecular network that is crucial for germination kinetics leading to memory of germinant exposure; the model reproduces experimental double germinant pulse germination curves. Analysis of the reconstructed network indicates that a minimal set of inactive and active GRs and a SpoVA channel in three states - closed inactive, closed active and open - is needed to reproduce memory. Spore germination memory is introduced in the network by the activation and deactivation rates of GRs, and by the interplay between activation of closed SpoVA channels and their rate of opening and closing.