Glycoprotein moiety in the cell wall of the red microalga Porphyridium sp. (Rhodophyta) as the biorecognition site for the Crypthecodinium cohnii-like dinoflagellate

Abstract

The Crypthecodinium cohnii-like heterotrophic dinoflagellate preys on the cells of the red microalga Porphyridium sp. UTEX 637, and not on other microalgae. The dinoflagellate contains enzymes that degrade the cell wall complex of this species of alga and not that of other red microalgae. The cells of the red microalgae are encapsulated within a cell wall complex composed of about 10 sugars, sulfate, and proteins. We previously hypothesized that the dinoflagellate recognizes the cell wall of this alga. In this study, we have shown that the biorecognition site is the 66-kDa glycoprotein in the algal cell wall complex. The methodology used in this study was based on changing the algal cell wall composition and examining the prey and chemosensory response of the dinoflagellate. The dinoflagellate was not attracted to the cell wall of other red microalgae, which are similar to that of Porphyridium sp., or to sugars composing its cell wall. However, the dinoflagellate preyed on and was attracted to Porphyridium sp. mutants (DCB resistant) having modified cell wall polysaccharide composition, probably because the 66-kDa cell wall glycoprotein was not changed. The dinoflagellate did not respond chemotactically to enzymatically degraded cell wall complex. Treatment of the cell wall complex with antiserum to the 66-kDa glycoprotein or with the lectin concanavalin A (con A), which binds specifically to α-D-mannosyl and α-D-glucosyl residues, did not affect the chemotactic attraction. However, prey by the dinoflagellate was prevented when the algal cells were blocked with antiserum specific to the 66-kDa glycoprotein or with con A. These latter results provide direct proof that the 66-kDa cell wall glycoprotein is the recognition site and prey-prevention results from the blocking of this site on the cell wall.