Distribution and partial characterization of ice-active molecules associated with sea-ice diatoms

Abstract

Macromolecular ice-active substances (IASs) that cause pitting of ice-crystal surfaces were previously shown to be associated with two species of Antarctic sea-ice diatom. Here it is shown that IASs are associated with many, if not all, sea-ice diatoms of McMurdo Sound, Antarctica, are present in the bottom layer of sea ice in rough proportion to the density of cells, and exist in winter-grown, algae-containing sea ice in different parts of the Southern Ocean and in at least one location in the Arctic. The IASs are retained to varying degrees by dialysis tubing with 50-, 100- and 300-kDa molecular weight cut-offs, suggesting a large molecular weight range, and have a solute requirement (∼≥200 mOsm/kg) for activity. The IASs occur as smears on both native and denaturing electrophoretic gels, which further suggests a heterogeneous nature. One apparently pure sample contained carbohydrate and protein (at an approximate 3:2 ratio on a weight basis), suggesting that the IASs are glycoproteins. The IASs preferentially bind to ice crystals, as they are concentrated in the ice phase of partially frozen solutions.