Low temperatures cause an increase in the non-covalent interactions between molecules. In other words, they cause molecular scale objects to "stick" together more favorably than they would at higher temperatures. This leads to the rigidification of cellular macromolecules and membranes which is a major cause of cellular death at low temperatures. A broad category of solutes, called chaotrophs, create more disorderly (i.e., less sticky) interactions at all temperatures, and therefore prevent molecular rigidity at low temperatures. In contrast, at moderate to high temperatures, the disordered interactions that chaotrophs promote lead to improper mechanics that cause cellular stress. Known chaotrophs include magnesium chloride, calcium chloride, glycerol, fructose, and urea. Conversely, a broad category of solutes called kosmotrophs perform in the exact opposite role; they promote non-covalent interactions between molecules which leads to poorer performance at low temperatures and higher performance at high temperatures.
The highly solute tolerant (xerotrophic) fungus Eurotium herbariorum has been documented accumulating environmental chaotrophs like fructose in its cells at low temperatures as well as synthesizing new ones like glycerol. The fungus actively shunned accumulation of kosmotrophs at these low temperatures. This accumulation/synthesis of more chaotrophs at low temperatures is likely to be partly responsible for the higher growth and survivability observed. Furthermore, evidence of relatively higher kosmotroph accumulation and synthesis at high temperatures correlated to higher survivability. Taken together, the evidence is highly suggestive that E. herbariorum is able to manipulate the molecular interactions within its cells to its benefit at low temperatures. The increased accumulation and synthesis of chaotrophs helps the cells maintain natural biochemical function at temperatures that would normally result in rigidity of molecules and cell death.Edit Summary
"[T]hese data demonstrated an apparently potent promotion of growth at low temperature by a chaotropic solute, irrespective of fungal species...a range of chemically diverse chaotropes (i.e., methanol, MgCl2, and glycerol)...Although the mechanisms by which diverse solutes exert chaotropic activity are not yet well-understood, the net effects of ionic, nonionic, and hydrophobic chaotropes may be indistinguishable to the cell...growth rates were greatly enhanced on all chaotrope-supplemented media relative to that on the kosmotropic medium at subzero temperatures...Whereas the growth rate was more than 200% higher on the kosmotropic sucrose medium relative to that observed on the chaotropic fructose medium at 30 °C, the converse was true at low temperatures (+5 °C and +1.7 °C)... [at low temperatures] Fungi grown on the sucrose-supplemented medium did not accumulate sucrose nor did they synthesize a kosmotropic-compatible solute such as trehalose, mannitol, arabitol, or erythritol...cells preferentially synthesized and accumulated a chaotropic-compatible solute, glycerol...Whereas conidia subjected to chaotrope treatments lost between 30% and 93% of their viability at high temperatures and high pressures (regardless of fungal species), there was virtually no loss of viability (≤5%) after a 24-h period of exposure to temperatures of −20 °C or − 80 °C. The converse trend was observed for kosmotrope-treated conidia, which lost up to 60% viability after exposure to low temperatures but survived relatively well (up to 96%) after exposure to high temperatures and pressures, regardless of the solute." (Chin et al. 2010:7836)
"[T]he solute activities of environmentally relevant substances determined the temperature windows for both survival and growth of microbial cells...mechanistic basis of this phenomenon correlates with the way in which physicochemically diverse stress parameters influence the structural interactions of cellular macromolecules. Whereas high temperatures and chaotropic activity disrupt interactions, factors such as desiccation, kosmotropic solutes, and low temperature promote interactions...microbial cells may be genetically hardwired to preferentially produce and/or accumulate chaotropic metabolites, such as glycerol and fructose, under conditions that promote macromolecular interactions to an extent that limits metabolic activity and cell division (e.g., temperatures close to and below 0 °C)." (Chin et al. 2010:7836-8)