Abstract
It is widely considered that most organisms cannot survive prolonged exposure to temperatures below 0°C, primarily because of the damage caused by the water in cells as it freezes. However, some organisms are capable of surviving extreme variations in environmental conditions. In the case of temperature, the ability to survive subzero temperatures is referred to as cryobiosis. We show that the ozobranchid leech, Ozobranchus jantseanus, a parasite of freshwater turtles, has a surprisingly high tolerance to freezing and thawing. This finding is particularly interesting because the leach can survive these temperatures without any acclimation period or pretreatment. Specifically, the leech survived exposure to super-low temperatures by storage in liquid nitrogen (−196°C) for 24 hours, as well as long-term storage at temperatures as low as −90°C for up to 32 months. The leech was also capable of enduring repeated freeze-thaw cycles in the temperature range 20°C to −100°C and then back to 20°C. The results demonstrated that the novel cryotolerance mechanisms employed by O. jantseanus enable the leech to withstand a wider range of temperatures than those reported previously for cryobiotic organisms. We anticipate that the mechanism for the observed tolerance to freezing and thawing in O. jantseanus will prove useful for future studies of cryopreservation.
Highlights
In most ectothermic organisms, prolonged exposure to temperatures below 0uC can cause the water in their tissues to freeze, resulting in permanent physiological damage and sometimes cell death
Because the four O. jantseanus hatchlings had not been provided with a blood meal before exposure to 290uC, the temperature tolerance observed in O. jantseanus is considered to be innate and not attributable to ingesta
Despite the gradual increase in mortality observed as the duration of low-temperature storage increased, these results showed that O. jantseanus was capable of surviving long-term cold storage (Fig. 2)
Summary
In most ectothermic organisms, prolonged exposure to temperatures below 0uC can cause the water in their tissues to freeze, resulting in permanent physiological damage and sometimes cell death. Several turtle species experience subzero temperatures (22 to 24uC) for 1 to 11 days in their hibernacula [10], and M. japonica and M. reevesii, the hosts of O. jantseanus, typically hibernate in environments where they are likely to periodically encounter temperatures as low as 0uC. The results showed that the leech was capable of surviving exposure to extremely low temperatures (2196uC) as well as prolonged storage at 290uC.
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