Fish frost protection with side effect

Newly discovered effect: antifreeze proteins also prevent the melting of ice

Antarctic ice fish: Antifreeze proteins enable survival in the icy Southern Ocean. © Uwe Kils / (CC BY-SA 3.0)
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Antimicrobial Paradox Effect: Protecting Antarctic fish does not only prevent the formation of ice crystals at low temperatures - they still do not melt emerging ice up to a degree above zero. Such an effect was previously unknown in biology, the researchers write in the journal Proceedings of the National Academy of Sciences. The fish obviously have to cope with this undesirable side effect somehow.

Ice-free below zero: Due to its salt content, the waters of the southern ocean do not freeze even at temperatures of minus 1.9 degrees Celsius. But for the body fluids of the fish in this frosty habitat, this is not true - so they form special antifreeze, so as not to freeze.

Frost protection does not work 100%

Particularly successful are the so-called Antarctic fish: they represent 75 percent of all fish species living in the Antarctic waters. The key to their success was probably their evolutionary key innovation of antifreeze: the anti-frost proteins that have been known for some time, however, allow the fish to survive even at temperatures below freezing, by binding water and preventing the formation of ice crystals. By contrast, many other species of fish disappeared from the previously warm southern ocean when Antarctica glaciated over the global slowdown some 35 million years ago.

Researchers led by Paul Cziko from the University of Oregon at Eugene have once again followed up on the properties of the biofree antifreeze and have discovered a surprising peculiarity: the antifreeze does not work 100% perfect. Wild Antarctic fish have tiny ice crystals in their bodies - despite the presence of antifreeze proteins. This was confirmed by Cziko and his colleagues by examining the fish in the laboratory. At temperatures below freezing, small ice crystals form in the body of the fish.

The second surprise followed as the researchers brought the temperatures above freezing: even at one degree Celsius plus, the ice crystals did not melt. Further analysis showed that the actual anti-frost proteins were responsible for this effect. These are also anti-tau proteins. display

First biological effect for over-heating of ice

"This discovery is, to our knowledge, the first example of a biological effect that allows the over-heating of ice, " says co-author Christina Cheng of the University of Illinois. "It is probably an undesirable side-effect that has arisen during the development of antarctic fish antifreeze proteins." Presumably, the acid-resistant crystals have a negative effect on the fish's organism. Similar to the fine fibers of asbestos, they could damage tissue structures, the researchers say.

They suspect that the fish have developed additional strategies to protect themselves from these effects: As most ice crystals accumulate in the spleen of the fish, we assume that there is a mechanism to remove them from the circulation, "says Cheng. According to her, the findings point to a fundamental principle of evolution: "Adjustments are usually associated with compromises: every evolutionary innovation probably also comes with disadvantages, " says the researcher.

(PNAS, 2014; doi: 10.1073 / pnas.1410256111)

(Cziko et al., PNAS, 23.09.2014 - MVI)