FOOD CAPTURE AND ADHESION BY THE HELIOZOON ACTINOPHRYS-SOL

The heliozoon Actinophrys sol is characterized by needle-like axopodia radiating from the spherical cell body. When heliozoons capture food organisms, the prey is caught by adhesion to the surface of axopodia w here numerous extrusomes are present close to the plasma membrane. To understand the molecular mechanism by which the heliozoons capture pre y organisms, crude isolation and characterization of the adhesive subs tance was carried out. Prey flagellates (Chlorogonium elongatum) adher ed and aggregated to remnants of heliozoon cells which had been killed by freezing or treatment at high temperature (80 degrees C for 10 min ). Isolated extrusomes, which were prepared as the supernatant of cell s homogenized and centrifuged after freezing and thawing, showed stron g adhesion to the prey flagellates which responded to the supernatant by adhering their flagella and cell bodies to each other to form bouqu et-like cell clusters. The adhesive substance was further extracted fr om heat-treated A. sol. This fraction contained filamentous material s imilar to the secreted contents of the extrusomes observed during feed ing. Its adhesive activity was not inhibited by trypsin treatment.