Proton Uptake by Dormant Bacterial Spores

摘要

Recently, the type of proton ionizable groups, their exact number, and equilibrium proton binding constant have been determined for dormant Bacillus subtilis spores [1] Kinetics of proton exchange between spores and surrounding aqueous solution supposes to be complicated mostly because of two coupled factors: a presumably high negative net charge and a multi-layered structure of the spore matrix. Indeed, in this work, we show by time-resolved micro-potentiometry [2] that proton uptake kinetics was a multi-step process involving a number of successively ~ 10-fold slower steps of proton penetration into the bulk and their binding to the ionizable groups within different layers of a spore structure. The important conclusion derived from the time constants systematically presented for the spore structural layers is that the effective diffusion coefficient for hydrogen ions within the spore core is significantly lower than the one within coats and cortex. Assuming the case of coupled proton diffusion and binding within the spore layers, the concentrations of ionizable groups in the spore compartments are estimated to be comparable with the gigantic spore proton capacity obtained from the data on proton equilibrium binding. In the practical point of view, regulation of the spore internal pH may be the way of its metabolic dormancy control, since the internal pH may be a contributing factor to enzymatic activity within the dormant spore.