Biomedical Engineering Reference
In-Depth Information
immobilise most organisms with which they come into contact (VandenSpiegel & Jangoux,
1987). The tubules, once expelled, are immediately adhesive on contact with a solid surface
(VandenSpiegel & Jangoux, 1987), such as the exoskeleton or skin of a predator. Crabs,
molluscs and sea stars can stimulate tubule expulsion, and the tubules stick to these species.
This adhesion happens entirely under water, and does not need the mixed environment of
the intertidal zone where many of the other potential adhesives are sourced.
Sticky tubules are found only within the family Holothuridae within the order
Aspidochirotida, and mostly in the genus Bohadschia and the genus Holothuria. Various
authors have described the ultrastructure of the tubules, especially for
H. forskåli
(Lawrence,
2001; VandenSpiegel & Jangoux, 1987; VandenSpiegel et al., 2000), as well as their expulsion
and release (Flammang et al., 2002) and the timeframe of regeneration (Flammang et al.,
2002; VandenSpiegel et al., 2000).
Flammang and Jangoux (2004) suggested, from the differences in the surface (adhesive)
protein types and compositions in
H. forskåli
and
H. maculosa
, that the adhesion proteins and
mechanism may differ between species. Other studies showed that adhesive strengths
varied between species, with the adhesion in
H. leucospilota
being several times greater than
for six other species (Flammang et al., 2002). A limited number of studies have probed the
mechanism of adhesion, focusing on
H. forskåli
and
H. leucospilota
(De Moor et al., 2003;
Müller et al., 1972; Zahn et al., 1973). These studies have shown that best adhesion is found
at temperatures, salinity and pH similar to those found in the marine environment in which
the organism flourishes, and is most effective with hydrophilic surfaces (Flammang et al.,
2002; Müller et al., 1972; Zahn et al., 1973). Increasing concentrations of urea led to a loss of
adhesion, suggesting that native protein structure(s) or interctions(s) may be required for
effective bonding (Müller et al., 1972). Later biochemical studies have also suggested that
the adhesive mechanism involves protein components (DeMoor et al., 2003).
In the present study, we have extended the information on Cuvierian tubule adhesion. In
this study we examined the tubules of a different species,
H. dofleinii
Augustin, 1908. We
have examined the distribution of the adhesive substance on the surface of expelled tubules,
along with the molecular weights and amino acid compositions of its main protein
components. We have estimated the strength of adhesion of
H. dofleinii
tubules to different
substrata, and examined the effects of salinity, pH, ionic strength and denaturants on the
adhesive properties.
2. Materials and methods
2.1 Collection of materials
Individual
H. dofleinii
were obtained from shallow subtidal seagrass banks in Moreton Bay,
Queensland, at a depth of about 1-2 metres at low tide, close to the western side of
Stradbroke Island (153 26.4' E 27 25.13' S to 27 25.68' S), and were held for up to 5 days
prior to use in filtered, recirculating seawater tanks at 21.5 - 22 C. The identification of the
animals was based on morphology, spicule shape and size and 18S-RNA sequencing (Peng
& Skewes, unpublished data).
2.2 Sample preparation
To collect expelled Cuvierian tubules,
H. dofleinii
individuals were held and gently
stimulated underwater until tubules were expelled. Immediately after expulsion, a tubule
was individually collected using polytetrafluoroethylene-tipped forceps, and was allowed
