Effects of hydration on molecular mobility in phase-bright Bacillus subtilis spores

The molecular mobility of P-31 and C-13 in dormant Bacillus subtilis spore samples with different water concentrations was investigated by high-resolution solid-state NMR. Lowest molecular mobility was observed in freeze-dried preparations. Rehydration to a 10% weight increase resulted in increases in molecular motions and addition of excess water furthered this effect. A spore slurry which had been freeze-dried displayed after addition of excess water similar NMR spectra to native wet preparations. Dipicolinic acid (DPA). which is mainly located in the core, was detected at all hydration levels in C-13 cross-polarization magic angle spinning (CPMAS) but not in single-pulse magic angle spinning (SPMAS) spectra, indicating that hydration had no effect on its mobility. The molecular mobility of (31)p, present mainly in core-specific components, was strongly dependent on hydration. This result suggests reversible water migration between inner spore compartments and the environment, whereas C-13 spectra of DPA indicate that it is immobilized in a water-insoluble network in the core. Scanning transmission electron microscopy revealed that freeze-dried spores were significantly longer and narrower than fully hydrated spores and had a 3% smaller volume.