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Bacterial Ice Nucleation in Monodisperse D2O and H2O-in-Oil Emulsions

Weng, Lindong, Tessier, Shannon N., Smith, Kyle, Edd, Jon F., Stott, Shannon L., Toner, Mehmet
Langmuir 2016 v.32 no.36 pp. 9229-9236
Pseudomonas syringae, aqueous solutions, atmospheric sciences, bacteria, cryopreservation, cryoprotectants, deuterium oxide, emulsions, ethylene glycol, food technology, freeze drying, freezing, freezing point, ice, ice nucleation, mixing, propylene glycol, solutes, sowing, temperature, trehalose, viability, water activity
Ice nucleation is of fundamental significance in many areas, including atmospheric science, food technology, and cryobiology. In this study, we investigated the ice-nucleation characteristics of picoliter-sized drops consisting of different D₂O and H₂O mixtures with and without the ice-nucleating bacteria Pseudomonas syringae. We also studied the effects of commonly used cryoprotectants such as ethylene glycol, propylene glycol, and trehalose on the nucleation characteristics of D₂O and H₂O mixtures. The results show that the median freezing temperature of the suspension containing 1 mg/mL of a lyophilized preparation of P. syringae is as high as −4.6 °C for 100% D₂O, compared to −8.9 °C for 100% H₂O. As the D₂O concentration increases every 25% (v/v), the profile of the ice-nucleation kinetics of D₂O + H₂O mixtures containing 1 mg/mL Snomax shifts by about 1 °C, suggesting an ideal mixing behavior of D₂O and H₂O. Furthermore, all of the cryoprotectants investigated in this study are found to depress the freezing phenomenon. Both the homogeneous and heterogeneous freezing temperatures of these aqueous solutions depend on the water activity and are independent of the nature of the solute. These findings enrich our fundamental knowledge of D₂O-related ice nucleation and suggest that the combination of D₂O and ice-nucleating agents could be a potential self-ice-nucleating formulation. The implications of self-nucleation include a higher, precisely controlled ice seeding temperature for slow freezing that would significantly improve the viability of many ice-assisted cryopreservation protocols.