as the aggregates increase in size and the primmorph or gel bead may act as seed for
axenic functional sponges. Further research should answer these issues. In all cases,
however, primmorphs and immobilised sponge cells are potentially interesting systems
for the production of sponge metabolites. The potential production mechanisms could be:
- Sponge biomass in primmorphs or in the support material grows. The particles are
harvested and secondary metabolites are recovered; - Sponge biomass in primmorphs or in the support material increases and differentiates
into functional sponges. The axenic sponges can be cultivated in closed controlled
bioreactors; - Sponge biomass in primmorphs or in the support material increases and at a certain
size excess biomass is excreted from the particles. Excreted cells are harvested and
secondary metabolites are recovered from the cells; - Primmorphs or immobilised sponge cells are used as a biofactory. Secondary
metabolites are excreted into the bioreactor medium and can be recovered from there.
Another fact that may cause problems in sponge cell cultures in relation to food is that
sponge cells ingest small organic particles and pass organic substances from cell to cell
rather than excreting it in the mesophyl. Hence, the capacity of sponge cells to take up
dissolved organic matter through their cell membrane might be limited, although it has
been shown that sponge cells can take up dissolved amino acids. In addition, it is not
known to what extent mammalian cell culture media can replace the natural diet of
sponges. Addition of marine-based food supplements (bacterial or algal extracts) may
increase the nutritive value of a sponge cell culture medium.
Especially in the case of primmorph or immobilised sponge cells that develop into
funtional sponges, the organisms could be fed as normal sponges; this means by food
particles. A possible strategy is growing the axenic sponges with media consisting of
micro-algae. The product is a photobioreactor in which micro-algae is fed to a sponge
bioreactor (Osinga et al., 1998).
Methods for cultivation of sponges and production of sponge metabolites are still in
the initial phases of development. The metabolites with bio-active properties are of high
value. For this reason it is highly worthwhile to continue this research. Recent progress
indicates that possibilities for sponge cultivation are realistic.
ACKNOWLEDGEMENTS
We thank Cindy Stoffelen for her contributions in the experiments with immobilised
sponge cells. We would like to thank Robin Willoughby for her help in making primary
cell lines. Rutger van Wielink is thanked for his work on primmorphs and Werner Müller
and Renate Steffen for all the valuable advise on the production of primmorphs.
REFERENCES
Adams C., Stevely J.M. and Sweat D. (1995) Economic feasibility of small-scale sponge fanning in
Pohnpei, Federated States of Micronesia. J. World Aquacult Soc 26 :132–142.
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