Identification of cell-substratum adhesion protiens from the diatom Phaeodactylum tricornutum

• Published in: Phycologia (Oxford) Vol. 48; no. 4
• Main Authors: Willis, A, Chiovitti, A, Bowler, C, Wetherbee, R
• Format: Journal Article
• Language: English
• Published: 01.07.2009
• Subjects: Bacillariophyceae; Phaeodactylum tricornutum
• ISSN: 0031-8884

Diatoms (Bacillariophyceae) are ubiquitous unicellular micro-algae, known for their ornate silicified cell walls and the secretion of extracellular polymeric substances (EPS). An important function of the EPS is adhesion, central to substratum attachment and motility. Diatoms are major contributors to the biofouling of submerged surfaces, causing great expense to shipping with reduced operational efficiencies and cleaning costs. The molecules involved in diatom cell adhesion remain unknown. Phaeodactylum tricornutum is a model organism for studying diatom biology; in this study the structure and nanophysical properties of the secreted EPS were investigated and an in silico analysis of the genome identified putative cell adhesion molecule genes. Light microscopy, scanning electron microscopy, and atomic force microscopy revealed that the cell is attached to the substratum by small tethers secreted principally from the girdle band region of the cell. These tethers accumulate on the substratum, become entangled, forming a biofilm. Eight genes were characterised in vivo by reverse-genetic techniques using over-expression and yellow-fluorescent-protein tagging. Protein localisation was ascertained by transmission electron microscopy and fluorescent scanning confocal microscopy. Cell adhesion strength was measured in a fully turbulent flow chamber, frequency of single molecule adhesion was quantified by atomic force microscopy and the visco-elastic properties of the EPS were characterised by quartz crystal micrograph. Three proteins, an integrin-like, a fasciclin-like and an uncharacterised, were found to have a significant affect on the cell substratum attachment strength of P. tricornutum. These are the first diatom adhesion proteins identified and these presented results are significant for diatom biology.