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First published online March 31, 2007
Journal of Experimental Biology 210, 1481-1488 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02759
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The role of calcium and magnesium in the concrete tubes of the sandcastle worm

ChengJun Sun1,*, Georg E. Fantner2, Jonathan Adams2, Paul K. Hansma2 and J. Herbert Waite1,3,*

1 Molecular, Cellular and Developmental Biology, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
2 Physics Department, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
3 Marine Science Institute and Chemistry and Biochemistry Department, University of California at Santa Barbara, Santa Barbara, CA 93106, USA


Figure 1
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  		Fig. 1. Set-up of miniature force gauge (A) and force calibration curve (B). Force was measured by the deflection of the stainless steel arm. The worm tube on a coverslip was secured to the spring arm by being sandwiched between a pair of magnets, as shown in the close-up picture of the deflection measurement set-up (C). Pull-out tests were viewed at a magnification of 40 using a binocular light microscope.

 

Figure 2
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  		Fig. 2. Morphology of Phragmatopoma californica cement following different treatments. (A-D) SEM views of untreated cement: adhesive footprint (A), zoom of dimpled surface (B), internal porosity revealed in fracture surface (C), and fracture surface with outer skin (D). (E-H) Comparable views of EDTA-treated cement: EDTA-treated cement deposit (E), zoom of dimpled surface following EDTA treatment (F), internal porosity of fractured cement that was broken prior to EDTA treatment (G), and internal porosity of cement fractured after EDTA treatment (H). (I). Energy dispersive X-ray spectroscopy of EDTA-treated (gray filled) and untreated cement (red trace).

 

Figure 3
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  		Fig. 3. (A) Distribution of pull-out force per sand grain as tested on EDTA-treated (N=81) and untreated sand (silica) tubes in seawater (N=134), and (B) the cumulative fraction plot of EDTA- and seawater-treated tubes showing that the difference between the two treatments was statistically significant.

 

Figure 4
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  		Fig. 4. Behavior of `wild', untreated laboratory-grown tubes and EDTA-treated laboratory-grown tubes subjected to compression. Inset shows SEM image of a piece of hybrid tube showing the original wild tube (right) extended with commercial acid-washed sand (left) by the resident worm. The table shows statistical results of the peak load ratio between different treatments.

 

Figure 5
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  		Fig. 5. Atomic force microscopy (AFM) of untreated and EDTA-treated cement deposits on glass coverslips. Each approach-retract curve represents an adhesive test performed on a single cement spot. An AFM cantilever with a glass bead attached to the end (A) is brought into contact with the edge of the cement and pressed down with 10 nN for 3 s. The EDTA curves are offset by –10 nN for clarity. With cantilever retraction, an adhesion force is measured (B) (curves are offset by 10 nN for better visibility). After 500 pulls at the same spot, the chamber was flushed with EDTA and 500 pulls were recorded at the initial spot. The pulling length, maximum force and energy dissipation were calculated for each trial (500 pulls for each condition on one sample). One trial is shown in (C); error bars represent s.d.; SW, seawater. (D) The repeatability and the time dependence of the adhesion for the trial shown in C, with each square representing one pull.

 

Figure 6
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  		Fig. 6. Models of the interfacial and cohesive paradigms of Ca/Mg involvement in the adhesion of Phragmatopoma californica cement. (A) Ca/Mg provides inter- and intramolecular bridges for Pc-3 proteins within the cement. (B) Ca/Mg provides interfacial bridges between cement proteins and anionic surface groups. The cross symbols indicate other types of interactions.

 




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