Abstract
Some bacteria such as the Bacillus and Clostridium species can form spores, which are the dormant form of vegetative bacteria and are highly resistant to physical and chemical stimuli, the sterilization of which requires heating at ～121°C for 30 min. A crucial factor that maintains this high-resistivity is the high concentration (～10% in dry weight of spore) of dipicolinic acid (DPA), which is spore-specific. We have applied 1H high-resolution high-pressure NMR spectroscopy, for the first time, to the spore suspension, and observed, directly and in real-time, the specific release of DPA molecules from the spore into the bulk water phase in response to a mild hydrostatic pressure (200 MPa) at 20°C. After the release of DPA, heat-treatment below ～100°C has proven to be sufficient to cause the inactivation of the spores. Direct observation of molecular processes in bacterial spores with high-pressure NMR in response to pressure and temperature perturbations shown here opens a new avenue for studying spores and vegetative cells directly at the molecular level.
