Biosilica deposition in the marine sponge Petrosia ficiformis (Poiret, 1789): the model of primmorphs reveals time dependence of spiculogenesis

Biomineralization is a phenomenon that spreads across all taxonomic kingdoms and has numerous potential applications in biotechnology. Using cell cultures (primmorphs) of Porifera as a model to study biosilicification, we hypothesised that different culture media can modulate siliceous spicule production both quantitatively and qualitatively. Long-term primmorph cultures of Petrosia ficiformis allowed comparing four experimental conditions: (1) natural seawater (SW) medium containing 5 μM silicate as control; (2) SW-Si 120 μM; (3) SW-Fe 5 μM; (4) SW-Si 60 μM Fe 2.5 μM evidencing several patterns of spiculogenesis. Here we have provided the first demonstration of how spiculogenesis processes are time-dependent and how spicules increase in number and size over time. The addition of dissolved silicon and low iron concentrations to the culture media produces larger spicules in greater numbers, affecting the proportions among spicule types as well. In particular, silicate seems to facilitate the production of fusiform oxeas, while iron stimulates the production of strongyloxeas. Considering the key role of spicules in taxonomic studies, our results point out the importance of environmental conditions in skeletal phenotypic plasticity, modulating the norm of reaction of the species.