Symbiosis, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 12 (1992) 19-31 Balaban, Philadelphia/Rehovot 19 zyxwvutsrqpon Macromolecules Associated wi t h the Cell Walls of Symbiotic Dinoflagella te s DOUGLAS A. MARKELL, ROBERT K. TRENCH and ROBERTO IGLESIAS-PRIETO Department of Biological Sciences and the Marine Science Institute University of California at Santa Barbara, Santa Barbara, CA 93106, USA Received December 30, 1990; Accepted May 18, 1991 Abstract One hypothesis often advanced to explain the observed specificity in algal- invertebrate symbioses is that macromolecules on the algal cell surface are lig- ands which interact with specific receptors on animal cell membranes. To ini- tiate a test of this hypothesis, we have isolated cell walls from the coccoid stage of four symbiotic dinoflagellate species, and have found that they contain a calcofluor-positive component consistent with cellulose. In addition, SDS- PAGE analysis of solubilised fractions of the walls revealed several proteins/ glycoproteins, ranging in molecular size from about 13.5 to zyxwvutsrqponmlkjihgfedcba > 200 kDa. This observation represents the first demonstration of proteins/ glycoproteins associ- ated with the cell walls of symbiotic dinoflagellates. We have also found that all four species of symbiotic dinoflagellate tested, release a range of water-soluble polypeptides/glycoproteins to the culture medium, raising the novel possibil- ity that released macromolecules, rather than cell wall-associated components, could be the recognition "signal( s )" passing between symbionts and hosts. Keywords: symbiosis, dinoflagellates, cell wall glycoproteins, extracellular glycopro- teins, recognition Abbreviations: SDS: sodium dodecyl sulphate; PAGE: polyacrylamide gel elec- trophoresis; PAS: periodic acid-Schiff reaction; HPLC: high perfor- mance liquid chromatography 0334-5114/92 /$03.50 @1992 Balaban