Freeze tolerance in a drosophilid fly

Košťál V., Zahradníčková H., Šimek P. (2011). Hyperprolinemic larvae of the drosophilid fly, Chymomyza costata, survive cryopreservation in liquid nitrogen. Proceedings of the National Academy of Sciences USA 108, 13035-13040.

Pictured is a scanning electron micrograph, in false color, of the front end of a larva of the drosophilid fly Chymomyza costata. The larva survives temperatures of -196°C in liquid nitrogen despite containing body fluids that can freeze into potentially lethal ice crystals. We examined the associations between the physiological and biochemical parameters of differently acclimated larvae and their freeze tolerance. Profiling of 61 different metabolites identified proline as a prominent compound whose concentration increased from 20 to 147 mM during diapause transition and subsequent cold acclimation. We increased the levels of proline in the larval tissues by feeding larvae proline-augmented diets and found that this simple treatment dramatically improved their freeze tolerance. Differential scanning calorimetry analysis suggested that high proline levels, in combination with a relatively low content of osmotically active water and freeze dehydration, increased the propensity of the remaining unfrozen water to undergo a glass-like transition (vitrification) and thus facilitated the prevention of cryoinjury.