FIG 4.

The time constants for H₂O-to-D₂O exchange are determined by fitting the kinetic traces shown in Fig. 3a and d and in Fig. S2 in the supplemental material to an exponential decay equation, y = a + b(1 − e^−t/τ). Under the flow conditions used for these experiments, it takes ∼200 ms to completely replace the fluid in the embedded channel. Time constants were not determined for spores in which the exchange appears to be complete by this time. Rather, we estimate an upper bound as our limit of detection (LOD), here assumed to be 0.09 s (yielding an exchange that is 90% complete after 200 ms), indicated by a horizontal line on the plot above. The results for Tb³⁺ sensitivity of l-valine germination and rates of dodecylamine germination (slow germination is <50% of the rate of fast germination) are taken from data in Fig. 5 and data not shown. −, minimal inhibition; +, intermediate inhibition; ++, nearly complete inhibition.