Fig. 1: Bacillus subtilis spores integrate over two consecutive germinant pulses.

(A) Bacterial spores can remain in dormancy (shaded area in blue) for years seemingly without any biological activity. It is thus unclear how spores sense environmental cues while dormant, and before triggering germination.

(B) Filmstrip from phase-contrast microscopy showing the fractional germination response to the pulses. Spores contained in a microfluidic chip were subjected to 3 min germinant pulses (10 mM L-alanine, dotted vertical lines) separated by 2-hour intervals. These pulses triggered germination of a subset of spores, detected by phase-contrast imaging: white dormant spores become phase dark when germinating as they rehydrate. Spores that maintain dormancy, despite exposure to germinant pulses, provoke the question of whether they can sense and process such environmental information. Scale bar indicates 5 μm.

(C) Single-cell time traces showing the change in the normalized phase-contrast intensity during spore germination (n = 200, subset of data from Fig. 1D). We note that collective fluctuations in the image intensity are due to subtle changes in camera focus.

(D) Fraction of dormant spores after each germinant pulse (n = 2,244). The abrupt decrease in the dormant fraction after the second germinant pulse indicates the ability of spores to integrate signals over consecutive pulses.

(E) The germination probability in each pulse is calculated based on the remaining dormant spores before each germinant pulse. The difference in the germination probability between the two pulses (vertical arrow) provides a metric to quantify the information integration by spores.

(F) Cartoon showing the main components of our mathematical model. The flux of potassium in a spore is assumed to depend partially on the difference between its internal (K_i) and external (K_e) concentrations, the K-channel conductance (g_k), and the membrane potential (V) of the spore. (G) The spore’s approach to the germination threshold is dictated by initial potassium content (K_i) and potassium efflux.

(H) In the mathematical model, the initial potassium content (K_i, t = 0) and the K-channel conductance (g_k) determine the potassium dynamics in spores (K_i(t)). These dynamics determine the spore’s propensity to germinate (See Box 1 and Supplementary Text).

(I) Simulated fraction of dormant spores after each germinant pulse.