Cryoprotectant treatment tests on three morphologically diverse marine dinoflagellates and the cryopreservation of Breviolum sp. (Symbiodiniaceae)

Dinoflagellates are among the most diverse group of microalgae. Many dinoflagellate species have been isolated and cultured, and these are used for scientific, industrial, pharmaceutical, and agricultural applications. Maintaining cultures is time-consuming, expensive, and there is a risk of contamination or genetic drift. Cryopreservation offers an efficient means for their long-term preservation. Cryopreservation of larger dinoflagellate species is challenging and to date there has been only limited success. In this study, we explored the effect of cryoprotectant agents (CPAs) and freezing methods on three species: Vulcanodinium rugosum, Alexandrium pacificum and Breviolum sp. A total of 12 CPAs were assessed at concentrations between 5 and 15%, as well as in combination with dimethyl sulfoxide (DMSO) and other non-penetrating CPAs. Two freezing techniques were employed: rapid freezing and controlled-rate freezing. Breviolum sp. was successfully cryopreserved using 15% DMSO. Despite exploring different CPAs and optimizing the freezing techniques, we were unable to successfully cryopreserve V. rugosum and A. pacificum. For Breviolum sp. there was higher cell viability (45.4 ± 2.2%) when using the controlled-rate freezing compared to the rapid freezing technique (10.0 ± 2.8%). This optimized cryopreservation protocol will be of benefit for the cryopreservation of other species from the family Symbiodiniaceae.

Rapid freezing of saturated clays under large thermal gradients

This study investigates the rapid freezing behavior of saturated clays under large thermal gradients. Although the freezing characteristics of soils under natural/low thermal gradients such as ice lens formation and water migration have been extensively studied, the freezing of a saturated soil under a large thermal gradient is not understood. This study presents rapid freezing tests to examine the freezing behavior of saturated fine-grained soils in a closed system under large thermal gradients using liquid nitrogen (LN). Temperatures are measured inside specimens during freezing and micro-CT visualized internally after freezing. Results show that large thermal gradients develop near the surfaces of specimens upon their submersion in LN. The specimens freeze homogeneously, and no visible ice lenses form, owing to the insufficient time for water migration and ice segregation under rapid freezing. The specimens fracture and split into major pieces, under no confining stresses in this study; freezing first occurs near the boundaries, and the freezing front propagates inward, creating temporal, differential volume changes between the outer and inner parts of the specimens, which leads to fractures in the unconfined state. The fractures affect subsequent temperature propagation and thermal gradients.

Cryopreservation of aromatic ginger Kaempferia galanga L. by encapsulation-dehydration

Kaempferia galanga L. is an endangered multi-purpose medicinal plant in Family Zingiberaceae, the rhizomes of which are used for several ayurvedic formulations. Encapsulation-dehydration (ED) method was optimized for cryopreservation of shoot tips of K. galanga. Shoot tips (STs) bearing the apical meristem dissected from the established in vitro shoot cultures were preconditioned in MS+0.4 M sucrose prior to encapsulation in calcium alginate and the beads subsequently transferred to MS liquid+0.3 M sucrose for 3 days afterward dehydration inside the laminar airflow for 4 hours upon rapid freezing in LN and rapid thawing produced maximum 62.2% survival and 46.7% regeneration rates. Shoot regeneration was observed from the apical meristems exclusive of intermediary callus phase. The plantlets regenerated from cryopreserved STs transferred to the field were phenotypically analogous with the mother plant.

Laboratory exploration of mineral precipitates from Europa's subsurface ocean

The precipitation of hydrated phases from a chondrite-like Na–Mg–Ca–SO4–Cl solution is studied using in situ synchrotron X-ray powder diffraction, under rapid- (360 K h−1, T = 250–80 K, t = 3 h) and ultra-slow-freezing (0.3 K day−1, T = 273–245 K, t = 242 days) conditions. The precipitation sequence under slow cooling initially follows the predictions of equilibrium thermodynamics models. However, after ∼50 days at 245 K, the formation of the highly hydrated sulfate phase Na2Mg(SO4)2·16H2O, a relatively recent discovery in the Na2Mg(SO4)2–H2O system, was observed. Rapid freezing, on the other hand, produced an assemblage of multiple phases which formed within a very short timescale (≤4 min, ΔT = 2 K) and, although remaining present throughout, varied in their relative proportions with decreasing temperature. Mirabilite and meridianiite were the major phases, with pentahydrite, epsomite, hydrohalite, gypsum, blödite, konyaite and loweite also observed. Na2Mg(SO4)2·16H2O was again found to be present and increased in proportion relative to other phases as the temperature decreased. The results are discussed in relation to possible implications for life on Europa and application to other icy ocean worlds.