Sterilization Resistance of Bacterial Spores Explained with Water Chemistry

Abstract

Bacterial spores can survive for long periods without nutrients and in harsh environmental conditions. This survival is influenced by the structure of the spore, the presence of protective compounds, and water retention. These compounds, and the physical state of water in particular, allow some species of bacterial spores to survive sterilization schemes with hydrogen peroxide and UV light. The chemical nature of the spore core and its water has been a subject of some contention and the chemical environment of the water impacts resistance paradigms. Either the spore has a glassy core, where water is immobilized along with other core components, or the core is gel-like with mobile water diffusion. These properties affect the movement of peroxide and radical species, and hence resistance. Deuterium solid-state NMR experiments are useful for examining the nature of the water inside the spore. Previous work in our lab with spores of Bacillus subtilis indicate that, for spores, the core water is in a more immobilized state than expected for the gel-like core theory, suggesting a glassy core environment. Here, we report deuterium solid-state NMR observations of the water within UV- and peroxide-resistant spores from Bacillus pumilus SAFR-032. Variable-temperature NMR experiments indicate no change in the line shape after heating to 50 °C, but an overall decrease in signal after heating to 100 °C. These results show glass-like core dynamics within B. pumilus SAFR-032 that may be the potential source of its known UV-resistance properties. The observed NMR traits can be attributed to the presence of an exosporium containing additional labile deuterons that can aid in the deactivation of sterilizing agents.

Picosecond orientational dynamics of water in living cells

“…Bacterial spores can survive extreme conditions (heat, toxic chemicals, drought) for very long periods by effectively “shutting down” their biochemistry. To explain how this happens, it has been proposed that in the core of spores (which contains very little water) water might be in a glass-like state 78 – 80 . However, NMR measurements indicate that this is not the case, and that the dormancy and heat resistance of spores probably result from protein immobilization 39 , 40 .…”

Water in cellulose: evidence and identification of immobile and mobile adsorbed phases by 2H MAS NMR

“…Besides adjacent to protein surfaces, water in proteins may also exist as deeply-buried and stronglyhindered molecules, which may undergo very slow exchange with the surrounding mobile water phase, and thus can be seen as a structural element of the protein. [12][13][14][15][16][17][18] Hence, understanding the state of immobile water molecules in hydrated natural polymers has a high biological relevance.…”

Bacillus pumilus SAFR-032 Genome Revisited: Sequence Update and Re-Annotation

“…As a result, B . pumilus SAFR-032 has been classified as an extreme microorganism according to the planetary protection standards [ 7 ], and established as an important reference organism in studies on bacterial spore viability [ 8 – 13 ]. The unique resistance of B .…”