ABSTRACT
A previous study used atomic force microscopy saw-tooth retraction curves to characterize the adhesive mucilage pads of the diatom Toxarium undulatum. The major mucilage component consisted of adhesive nanofibers (ANFs) made up of modular proteins arranged into cohesive units, each containing a set number of modular proteins aligned in parallel. This study shows that T. undulatum adhesive mucilage is a biocomposite containing four additional adhesive components, including single modular proteins that are likely to be the structural units from which the ANFs are assembled. Two further distinct supramolecular assemblies were observed to coexist with ANFs (ANFs II and III), along with a continuum of single modular proteins through oligomers made up of varying numbers of modular proteins arranged in parallel. All components of the adhesive biocomposite produce a characteristic force spectrum with the same interpeak distance (35.3 +/- 0.3 (mean +/- SE) nm), suggesting they are derived from discrete supramolecular assemblies of the same modular protein, but they are distinguishable from one another based on the rupture force, persistence length, and interpeak force measured from their saw-tooth curves.
Subject(s)
Diatoms/metabolism , Proteins/chemistry , Cells, Cultured , Diatoms/cytology , Microscopy, Atomic Force , Proteins/metabolism , Tissue AdhesionsABSTRACT
The adhesive and mechanical properties of a cell-substratum adhesive secreted by live diatom cells were examined in situ using atomic force microscopy. The resulting force curves have a regular saw-tooth pattern, the characteristic fingerprint of modular proteins, and when bridged between tip and surface can repeatedly be stretched and relaxed resulting in precisely overlaying saw-tooth curves (up to approximately 600 successive cycles). The average rupture force of the peaks is 0.794 +/- 0.007 (mean +/- SE) nN at a loading rate of 0.8 microm/s and the average persistence length is 0.026 +/- <0.001 (mean +/- SE) nm (fit using the worm-like chain model). We propose that we are pulling on single adhesive nanofibers, each a cohesive unit composed of a set number of modular proteins aligned in register. Furthermore, we can observe and differentiate when up to three adhesive nanofibers are pulled based upon multimodal distributions of force and persistence length. The high force required for bond rupture, high extensibility (approximately 1.2 microm), and the accurate and rapid refolding upon relaxation, together provide strong and flexible properties ideally suited for the cell-substratum adhesion of this fouling diatom and allow us to understand the mechanism responsible for the strength of adhesion.
Subject(s)
Algal Proteins/chemistry , Algal Proteins/ultrastructure , Cell Adhesion Molecules/chemistry , Cell Adhesion Molecules/ultrastructure , Diatoms/enzymology , Nanostructures/chemistry , Nanostructures/ultrastructure , Adhesiveness , Cells, Cultured , Computer Simulation , Elasticity , Enzyme Activation , Models, Chemical , Models, Molecular , Particle Size , Peptide Mapping , Protein Conformation , Tensile StrengthABSTRACT
Recent demands for non-toxic antifouling technologies have led to increased interest in coatings based on silicone elastomers that 'release' macrofouling organisms when hydrodynamic conditions are sufficiently robust. However, these types of coatings accumulate diatom slimes, which are not released even from vessels operating at high speeds (>30 knots). In this study, adhesion strength and motility of three common fouling diatoms (Amphora coffeaeformis var. perpusilla (Grunow) Cleve, Craspedostauros australis Cox and Navicula perminuta Grunow) were measured on a poly-dimethylsiloxane elastomer (PDMSE) and acid-washed glass. Adhesion of the three species was stronger to PDMSE than to glass but the adhesion strengths varied. The wall shear stress required to remove 50% of cells from PDMSE was 17 Pa for Craspedostauros, 24 Pa for Amphora and >>53 Pa for Navicula; the corresponding values for glass were 3, 10 and 25 Pa. In contrast, the motility of the three species showed little or no correlation between the two surfaces. Craspedostauros moved equally well on glass and PDMSE, Amphora moved more on glass initially before movement ceased and Navicula moved more on PDMSE before movement ceased. The results show that fouling diatoms adhere more strongly to a hydrophobic PDMSE surface, and this feature may contribute to their successful colonization of low surface energy, foul-release coatings. The results also indicate that diatom motility is not related to adhesion strength, and motility does not appear to be a useful indicator of surface preference by diatoms.
