FLOW-CYTOMETRIC CHARACTERIZATION OF THE CELL-SURFACE GLYCANS OF SYMBIOTIC DINOFLAGELLATES (SYMBIODINIUM SPP.)

Symbiodinium spp. dinoflagellates are common symbionts of marine invertebrates. The cell-surface glycan profile may determine whether a particular Symbiodinium is able to establish and maintain a stable symbiotic relationship. To characterize this profile, eight Symbiodinium cultures were examined using eight glycan-specific fluorescent lectin probes. Confocal imaging and flow-cytometric analysis were used to determine significant levels of binding of each probe to the cell surface. No significant variation in glycan profile was seen within each Symbiodinium culture, either over time or over growth phase. No cladal trends in glycan profile were found, but of note, two different Symbiodinium cultures (from clades A and B) isolated from one host species had very similar profiles, and two other cultures (from clades B and F) from different host species had identical profiles. Two lectin probes were particularly interesting: concanavalin A (ConA) and Griffonia simplicifolia-II (GS-II). The ConA probe showed significant binding to all Symbiodinium cultures, suggesting the widespread presence of cell-surface mannose residues, while the GS-II probe, which is specific for glycans possessing N-acetyl groups, showed significant binding to six of eight Symbiodinium cultures. Other probes showed significant binding to the following percentage of Symbiodinium cultures examined: wheat germ agglutinin (WGA), 37.5%; peanut agglutinin (PNA), 50%; Helix pomatia agglutinin (HPA), 50%; phytohemagglutinin-L (PHA-L), 62.5%; soybean agglutinin (SBA), 50%; and Griffonia simplicifolia-IB₄ (GS-IB₄), 12.5%. This study highlights the complexity of cell-surface glycan assemblages and their potential role in the discrimination of different dinoflagellate symbionts by cnidarian hosts.