Integrated Microscopy of Extracellular Adhesives of the Marine Biofouling Alga Achnanthes Longipes (Bacillariophyceae)

An integrated approach including TEM, SEM and LM was utilized to investigate adhesives produced by the marine fouling diatom Achnanthes longipes. Extracellular adhesive secretion during sequential attachment in living diatom cells was examined using video microscopy. A suite of cryotechniques including high pressure freezing (HPF), freeze-substitution (FS) and high resolution cryo-field-emission SEM (cryo-FESEM) were required for preservation and structural investigation of the hydrophilic polymers synthesized by A. longipes that promote attachment to ship hulls, oil rigs and other submerged structures.Living cells and associated extracellular biocomposites were rapidly cryo-immoblized and observed using a Hitachi S-900 FESEM equipped with a cryo-stage. This technique allowed resolution of details of polymer organization within the pad, shaft and collar portions of the major adhesive structure termed a stalk (Fig. 1,2). This stalk has been demonstrated to consist mainly of polysaccharide cross-linked by O-linked polypeptides. In addition to permanently adhering the diatom to the substratum, the stalk elevates A. longipes, possibly enhancing the ability to successfully compete with other biofilm dwellers.