MASTER THESIS Biomimetic potential of sponge ... - IAP/TU Wien

Recently, various reviews have summarized the steps involved in spiculogenesis (Wang et
al., 2012c) (Wang et al., 2012b) (Müller et al., 2009c) focussing on different processes
suggested for bioprospecting (Wang et al., 2011a) (Hayden, 2003), including biomimetic and
biotechnological perspectives. Three major stages have been proposed by Müller and
colleagues (2009c):
(i)
(ii)
(iii)
Intracellular phase (initial growth)
Extracellular phase (consecutive appositional growth)
Extracellular phase (final morphogenesis)
It is essential to recognize that spiculogenesis, like other types of biologically controlled
biomineralization, takes place at near neutral pH (6-8), ambient temperature and pressure
(Cha et al., 1999).
This process is quite fast, and accordingly difficult to observe in adult sponges. At an
ambient temperature of 21°C for example the synthesis of a spicule with a diameter of 6-
8 µm and a length of 190 µm is completed after 40 hours (Weissenfels, 1984). Therefore,
much of the evidence here has first been gained in vitro, as is common in molecular biology.
A novel technique, however, was the introduction of a 3D cell culture, the so-called
primmorphs that allow experiments in a near-natural environment. These primmorphs
consist of pluripotent stem cells (cells that can differentiate to become any cell type) and the
spicule forming sclerocytes of the demosponge Suberites domuncula (Imsiecke et al., 1995)
(Custodio et al., 1998). Since these cell cultures, like the actual sponge they are derived
from, mainly form monactinal, straight megascleres (Müller et al., 2005), much of the
present knowledge summarized here specifically holds for this type of spicules.
Initial growth
Silicon is present in seawater at low concentrations (≤10 µM), mainly in the form of
orthosilicic acid (Si(OH) 4 ) (Fröhlich & Barthel, 1997). In Suberites domuncula, Schröder and
co-workers (2004) found a transport protein that mediates the import of Si(OH) 4 into
specialized cells (Figure 13a). This ability to extract silica from aqueous media with very low
concentrations distinguishes the biomineralization in sponges from all other silica
mineralizing organisms, like diatoms, that rely on super-saturated concentrations of silica in
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