Self-assembling processes are central to the supramolecular organization and pattern formation found in all biological organisms. Diatoms rely on self-assembled extracellular biocomposites for cell motility and permanent adhesion to surfaces. Due to the resilience of these biocomposites, diatoms are important constituents of aquatic biofouling communities. The impact of biofouling is widely felt in cost for remediation and degraded performance. The physical characteristics of diatom adhesives, such as high flexibility, tensile strength, and resistance to shearing forces and bacterial contamination, make diatom adhesion an interesting model system for the study of extracellular matrix biogenesis, one that can be easily manipulated and studied.

We have pursued an integrated approach encompassing biochemical, microscopical and molecular methods in an attempt to further define diatom adhesion and motility in Achnanthes longipes, a common marine fouling diatom. The extracellular components that perform motility and adhesion functions are closely related to one another and are predominately proteoglycan-like molecules with the major polysaccharide a fucoglucuronogalactan (FGG). We have delineated the sequence of events involved in attachment of the diatoms to a variety of substrata using time-lapse digital video microscopy and are currently applying 4-D microscopy and advanced cryo-SEM and TEM methods to track biogenesis. The adhesive structures are not assembled in the presence of high concentrations of iodide, and bromide is a limiting requirement for adhesion, which, combined with other evidence, suggests a bromoperoxidase mediated cross-linking of ECM polymers. We are currently localizing specific carbohydrate and protein moieties of the adhesive with antibodies, lectins and other probes conjugated with colloidal gold and labeling high pressure frozen and freeze substituted cells. We have produced a suite of monoclonal/polyclonal antibodies against the adhesives and are using these as probes of structure/function of the adhesives. We have created an expression cDNA library of Achnanthes and analyzed expressed sequence tags from this library and we have isolated a putative haloperoxidase gene from A. longipes that may be involved in phenolic crosslinking of polymers.

This work is of significant import because: 1) Diatoms are an integral component of biofouling communities. Biofouling causes significant reduction in fuel efficiency thereby wasting valuable energy resources (estimated costs - $100 million/yr.). Remediation of biofouling also wastes significant resources and creates toxic wastes (estimated dry-dock and disposal costs - $400 million/yr.); 2) Adhesives that are effective in aqueous saline environments are sought for dental and medical applications as well as for use in maintenance and repair of a variety of submerged structures. The information generated by detailed biochemical characterization of extracellular polymers should be applicable in the identification/ development of new adhesives for these uses, and; 3) Diatom extracellular adhesive biogenesis represents a unique and interesting model system in which to study self-assembling processes that are central to the supramolecular organization and pattern formation required of all organisms.

For more information on this subject, see:

Wustman 1998

Wustman 1997

Gretz 1998