Atomistic Study of Wet-heat Resistance of Calcium Dipicolinate in the Core of Spores
- PDF / 1,503,508 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 60 Downloads / 156 Views
MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.68
Atomistic Study of Wet-heat Resistance of Calcium Dipicolinate in the Core of Spores Ankit Mishra1, Pankaj Rajak1, Subodh Tiwari1, Chunyang Sheng1, Aravind Krishnamoorthy1, Aiichiro Nakano1, Rajiv Kalia1, Priya Vashishta1 1Collaboratory for Advanced Computing and Simulations, University of Southern California, Los Angeles, CA 90089
ABSTRACT
The extreme heat resistance of dormant bacterial spores strongly depends on the extent of protoplast dehydration and the concentration of dipicolinic acid (DPA) and its associated calcium salts (Ca-DPA) in the spore core. Recent experiments have suggested that this heat resistance depends on the properties of confined water molecules in the hydrated Ca-DPArich protoplasm, but atomistic details have not been elucidated. In this study, we used reactive molecular dynamics (RMD) simulations to study the dynamics of water in hydrated DPA and Ca-DPA as a function of temperature. The RMD simulations indicate two distinct solid-liquid and liquid-gel transitions for the spore core. Simulation results reveal monotonically decreasing solid-gel-liquid transition temperatures with increasing hydration. Additional calculations on the specific heat and free energy of water molecules in the spore core further support the higher heat resistance of dehydrated spores. These results provide an insight into the experimental trend of moist-heat resistance of bacterial spores and reconciles previous conflicting experimental findings on the state of water in bacterial spores.
INTRODUCTION Some bacteria transform to their spore forms to survive under unfavorable conditions for extended periods of time [1,2]. Endospores of Bacillus species are highly resistant to a variety of environmental stresses including toxic chemicals, radiation and heat. Heat resistance of bacterial spores is commonly attributed to a combination of protoplast dehydration, mineralization and thermal adaptation of genetics, among which dehydration is considered to be the primary factor. In fact, prior studies demonstrated a strong correlation between increasing water content and decrease in heat resistance in the range of protoplast water content between 28% and 57% by weight [3]. This correlation is reflected in the remarkable heat resistance of spores to temperatures up to 45 C greater than the viability limit of vegetative cells, and it underpins the moist-heat treatment that is widely used to kill bacterial spores. One of the primary factors responsible for spore’s moist-heat resistance is the high concentration of dipicolinic acid (DPA) and associated divalent cations
Downloaded from https://www.cambridge.org/core. Teachers College Library - Columbia University, on 25 Jan 2018 at 13:15:44, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms . https://doi.org/10.1557/adv.2018.68
(mostly Ca) in the spore core [4,5]. However, the molecular mechanisms describing the origin of heat resistance due to Ca-DPA, as we
Data Loading...
