| Achnanthes longipes, Amphora coffeaeformis, and Cymbella cistula are biofouling diatoms that attach to submerged substrata by secretion of extracellular matrix (ECM) components. A. coffeaeformis adheres to surfaces via capsules while A. longipes and C. cistula attach by stalks. The stalks of A. longipes consist of a cell-associated collar, a surface adhered pad, and a shaft, which separates the pad from the cell.; A. longipes shafts consisted of a central core containing highly sulfated fucoglucuronogalactans (FGGs), and a central ribbon and outer layers made up of less sulfated FGGs. FGGs were {dollar}cong{dollar}100,000 molecular mass and cross-linked by proteins/glycoproteins via O-glycosidic linkages. Monoclonal antibodies (AL.C1-4) and antibodies from two uncloned hybridomas recognized carbohydrate complimentary regions on FGGs, and antigenicity was dependent on fucosyl-containing side chains. Antibody and lectin localization indicated that FGGs were involved in cell motility, initial adhesion, and stalk assembly. During stalk synthesis, less sulfated FGGs were expelled through pores surrounding the raphe and formed a cylinder, which contained highly sulfated FGGs expelled from the raphe. Highly sulfated FGGs made up the central core and acted as a highly pliable gel-like material, flexible and resistant to desiccation, while less sulfated FGGs were closely associated and formed tightly knit fibrils observed in outer stalk layers. Covalent and cationic cross-bridged FGG fibrils were oriented parallel to the length of the shaft, which added strength and produced sturdy, flexible stalk structures.; C. cistula stalks consisted of sulfated xylogalactans and a small amount of protein, and were expelled through the apical pore field and assembled via cationic cross-bridging. Xylogalactans consisted of a sulfated galactan backbone with xylosyl-containing side chains. Antibodies raised against A. longipes did not recognize C. cistula adhesives. A. coffeaeformis adhesives were composed of polymers similar to A. longipes FGGs and cross-reacted with AL.C1.; The chemistry of diatom ECM was unique from that of other algae, fungi, and higher plants, however, the mechanisms of assembly were similar. Since the adhesive stalks were self-assembled into structures that are more distinct and possibly less complex than those of fungi, higher plants, and animals, diatoms provide a unique model system of ECM assembly. |
