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Adhesive Modular Proteins Occur in the Extracellular Mucilage of the Motile, Pennate Diatom Phaeodactylum tricornutum

School of Botany, University of Melbourne, Victoria 3010, Australia

Correspondence: Address reprint requests and inquiries to Richard Wetherbee, Tel.: 613-834-45057; E-mail: richardw{at}unimelb.edu.au.

This Letter reports on adhesive modular proteins recorded by atomic force microscopy on live cells from the extracellular mucilage secreted from, and deposited around, the motile form of the pennate diatom Phaeodactylum tricornutum. This is the first report of modular proteins and their supramolecular assemblies, called adhesive nanofibers (ANFs), to be found on diatoms that use adhesives not only for substratum adhesion, but as a conduit for cell motility. The permanent adhesive pads secreted by Toxarium undulatum, a sessile centric diatom, were previously shown to possess ANFs with a modular protein backbone. Our results reported here suggest that modular proteins may be an important component of diatom adhesives in general, and that diatoms utilize the tensile strength, toughness, and flexibility of ANFs for multiple functions. Significantly, the genome of P. tricornutum has recently been sequenced; this will allow directed searches of the genome to be made for genes with modular protein homologs, and subsequent detailed studies of their molecular structure and function.