Bacterial spores as natural ionic nanoreservoirs: Physicochemical characterization

PHYS 266

Sergey V. Kazakov, skazakov@pace.edu, Department of Chemistry and Physical Sciences, Pace University, 861 Bedford Road, Pleasantville, NY 10570 and Irina G. Gazaryan, igazarya@burke.org, Burke Medical Research Institute, 785 Mamaroneck Ave, White Plains, NY 10605.
Bacterial spores in dormant state are considered as natural ionic reservoirs. Number of binding sites per spore and apparent binding constant are the quantitative physicochemical characteristics of an ionic reservoir. It was found that the proton capacity of each Bacillus subtilis spore can reach gigantic values of ~1010 binding sites/spore. The obtained pKa value of 4.7 indicate that carboxyl groups are the major ionizable groups within a spore matrix. Kinetics of proton exchange between dormant B. subtilis spores and environment was examined to discover a multi-step process of proton uptake consisting of a fast (< 1 sec) proton binding on the surface of a spore and a number of successively 10-fold slower steps of penetration of protons inside the bulk and their binding to the ionizable groups within different layers of a spore structure. Estimated from a model of coupled diffusion and binding, the concentrations of binding sites for protons inside the spore layered structure appeared to be comparable with the spore proton capacity found from the equilibrium binding. Both the gigantic proton capacity and the multi-step mechanism of ions uptake into the spore ionic reservoir may be the constituents of the same resistance mechanism allowing spores to tolerate a significant and fast change in the environmental ionic conditions.