A mathematical kinetic model of memory in Bacillus subtilis spore germination

Dormant Bacillus subtilis spores germinate through interaction of germinants with germinant receptors (GRs). Subsequently, GR signals are transduced to SpoVA protein channels, and opening these channels leads to calcium dipicolinic acid (CaDPA) release and completion of germination. Spores exhibit memory in germination, as spores given a short germinant pulse more readily respond to a second pulse. We developed a mathematical model to identify the minimal network crucial for germination kinetics leading to memory of germinant exposure, and reproducing 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 GR's activation and deactivation rates and the interplay between activation of closed SpoVA channels and their rates of opening and closing.