CALLOW, J.A.: Cellular and materials characterisation of the Enteromorpha spore adhesive

Motile spores of the biofouling alga Enteromorpha attach to marine substrata through the secretion of a glycoprotein adhesive. AFM and ESEM studies of the topography and materials properties of adhered spores reveal the secreted adhesive to be a hydrophilic, swollen, gel-like pad, approximately 1 μm thick. Freshly released adhesive has a maximum adhesion force of 200 nN and a compressibility (modulus) of 0.54 x 10⁶ N m^-2. After release the adhesive undergoes progressive ‘curing’ becoming less ‘sticky’ and ‘stiffer’ within 60 min. Hydrodynamic studies with mixed alkane thiol SAMs and elastomers show that adhesion is strongly influenced by surface energy and substratum modulus. Progress towards the molecular characterisation of the adhesive has used monoclonal antibody (mAb) technology. MAb Ent 6 immunolabels material secreted during the early stages of adhesion and inhibits spore adhesion. The antigen is absent from the cytoplasm or organelles of vegetative tissue but labels the vegetative cell wall suggesting a relationship between cell wall components and materials involved in primary adhesion. Ent 6 labels the Golgi region of settled spores and recognises a 110 kDa N-linked polydisperse and heterogeneous glycoprotein in Western blots of extracts of swimming spores under denaturing conditions. The antigen becomes progressively cross-linked after zoospore attachment In native form the antigen is a high molecular weight aggregate (Mr >1.3 x10⁶). A model for zoospore adhesion is discussed in which adhesion is viewed as an extension of cell wall synthesis, with cross-links between glycoproteins and other cell wall matrix components providing a strong physical continuum between the cell and the adhesive at the substratum interface.