Ice Nucleation Activity in the Freezing-Tolerant Antarctic NematodePanagrolaimus davidi

Ice nucleation spectrometry was used to look for the presence of ice nucleating agents (INAs), and their inhibitors, in cultures ofPanagrolaimus davidi, an Antarctic nematode which survives intracellular freezing. INA activity was absent in both nematode suspensions and homogenates. The nematodes produce a substance which inhibits the nucleation activity of organic INAs but not of an inorganic INA (AgI). The nucleation inhibitor is both released from the nematode by homogenization and excreted by them into the medium, but the former was more effective at inhibiting nucleation. The inhibitory activity was destroyed by heating. A thermal hysteresis protein, or a similar ice-active substance, may be responsible for the nucleation inhibition.