SUBSTRATUM ADHESION AND GLIDING IN A DIATOM ARE MEDIATED BY EXTRACELLULAR PROTEOGLYCANS

Diatoms are unicellular microalgae encased in a siliceous cell wall, o r frustule. Pennate diatoms, which possess bilateral symmetry, attach to the substratum at a slit in the frustule called the raphe. These di atoms not only adhere, but glide across surfaces whilst maintaining th eir attachment, secreting a sticky mucilage that forms a trail behind the gliding cells. We have raised monoclonal antibodies to the major c ell surface proteoglycans of the marine raphid diatom Stauroneis decip iens Hustedt. The antibody StF.H4 binds to the cell surface, in tile r aphe and to adhesive trails and inhibits the ability of living diatoms to adhere to the substratum and to glide. Moreover, StF.H4 binds to a periodate-insensitive epitope on four frustule-associated proteoglyca ns (relative molecular masses 87, 112, and > 200 kDa). Another monoclo nal antibody, StF.D5, binds to a carbohydrate epitope on the same set of proteoglycans, although the antibody binds only to the outer surfac e of the frustule and does not inhibit cell motility and adhesion.