Marine diatom growth on different forms of particulate silica: evidence of a cell/particle interaction

The influence of particulate silica sources on growth and silicon uptake of 3 diatom species: Cylindrotheca fusiformis, Navicula sp., and Skeletonema costatum, was investigated. Each diatom strain was incubated in controlled conditions, with mineral (quartz sand and 2 pure quartz dusts with variable degree of hydrophilicity/hydrophobicity) and biogenic (diatomaceous earth and sponge spicules) silica substrates. Mineral sources were all crystalline, while the biogenic substrates were mostly amorphous. Each diatom species showed a different growth pattern with the various particulate silica substrates, none of which related to the rate of silicon dissolution in the growth medium: S. costatum grew better in presence of the quartz sand; while Navicula sp. and C. fusiformis showed higher growth values with the hydrophobic quartz particles. In contrast, low levels of growth of the 3 diatoms were found in the presence of the biogenic amorphous silica substrates. The high values of the silicon uptake of all diatom species in the presence of the crystalline substrates in culture conditions seemed to confirm the preferred exploitation of the dissolved silicon from crystalline sources with respect to the amorphous mineral substrates. Thus, it could be hypothesized that the dissolved silicon uptake by marine diatoms was not only mediated by solubilized oligomeric silica, but a direct interaction between diatom cell and particulate mineral substrates. Such chemical/physiological interaction can be highly specific either for the different diatom species or silica particles. A chemical model of a possible role of some organic compounds involved in the uptake of dissolved silicon from particulate silica sources by marine diatoms was suggested, and the potential ecological significance of these findings is discussed.