Meeting Abstract

P3.209  Tuesday, Jan. 6  Natural ice nucleating bacteria increase the freezing tolerance of the intertidal bivalveGeukensia demissa MCCORKLE, A.M.*; LOOMIS, S.H.; Connecticut College shloo@conncoll.edu

Instead of avoiding freezing, freeze tolerant invertebrates actively initiate controlled ice nucleation at relatively high sub-zero temperatures in extracellular compartments. Most produce proteinaceous ice-nucleators in their hemolymph, however the intertidal bivalve mollusc Geukensia demissa lacks this ability and instead utilizes a natural ice-nucleation active (INA) bacterium (Pseudomonas fulva) to induce crystallization in the pallial fluid. In this study, two additional INA bacteria strains were isolated from the palial fluid of Geukensia: Psychrobacter sp. and Shewanella sp. The ice-nucleation activity of both strains was characterized and Psychrobacter was found to consistently induce nucleation at temperatures 1-3C higher than Shewanella. The presence of Psychrobacter in the palial fluid of warm acclimatized Geukensia significantly decreased the LT₅₀ from -12.5C to -15.0C, close to LT₅₀ of winter acclimatized specimens (-16.5C). Gills from summer acclimatized Geukensia, had 12% more cell damage than gills without added bacteria when frozen at -13.5C. There was no significant difference between the treatments when frozen at -10C or -15C. These results show that ice nulceators alone can significantly increase freezing tolerance in Geukensia but do not explain the entire increase in freezing tolerance of winter acclimatized animals.