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Published online on June 11, 2007, 10.1073/pnas.0608980104
PNAS | June 19, 2007 | vol. 104 | no. 25 | 10441-10446


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BIOLOGICAL SCIENCES / BIOPHYSICS
Salinity-dependent diatom biosilicification implies an important role of external ionic strength

Engel G. Vrieling*,{dagger}, Qianyao Sun{ddagger}, Mingwen Tian§, Patricia J. Kooyman, Winfried W. C. Gieskes||, Rutger A. van Santen**, and Nico A. J. M. Sommerdijk{dagger}{dagger}

*Groningen Biomolecular Sciences and Biotechnology Institute and ||Department of Ocean Ecosystems, Center for Ecological and Evolutionary Studies, University of Groningen, P.O. Box 14, NL-9750 AA Haren, The Netherlands; {ddagger}State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China; §Nano Technology Instruments, Europe BV, Arnhemseweg 34, NL-7331 BL Apeldoorn, The Netherlands; DelftChemTech and National Centre for High Resolution Electron Microscopy, Delft University of Technology, Julianalaan 136, NL-2628 BL Delft, The Netherlands; and **Schuit Institute of Catalysis and {dagger}{dagger}Soft Matter Cryo-Transmission Electron Microscopy Unit, Department of Biomedical Engineering, Eindhoven Technical University, P.O. Box 513, NL-5600 MB Eindhoven, The Netherlands

Edited by Richard Gordon, University of Manitoba, Winnipeg, MB, Canada, and accepted by the Editorial Board May 9, 2007 (received for review October 12, 2006)

The role of external ionic strength in diatom biosilica formation was assessed by monitoring the nanostructural changes in the biosilica of the two marine diatom species Thalassiosira punctigera and Thalassiosira weissflogii that was obtained from cultures grown at two distinct salinities. Using physicochemical methods, we found that at lower salinity the specific surface area, the fractal dimensions, and the size of mesopores present in the biosilica decreased. Diatom biosilica appears to be denser at the lower salinity that was applied. This phenomenon can be explained by assuming aggregation of smaller coalescing silica particles inside the silica deposition vesicle, which would be in line with principles in silica chemistry. Apparently, external ionic strength has an important effect on diatom biosilica formation, making it tempting to propose that uptake of silicic acid and other external ions may take place simultaneously. Uptake and transport of reactants in the proximity of the expanding silica deposition vesicle, by (macro)pinocytosis, are more likely than intracellular stabilization and transport of silica precursors at the high concentrations that are necessary for the formation of the siliceous frustule components.

biosilica | silica nanostructure | silicification | silica chemistry

Author contributions: E.G.V. and Q.S. contributed equally to this work; E.G.V. designed research; E.G.V., Q.S., M.T., and P.J.K. performed research; E.G.V., Q.S., M.T., P.J.K., W.W.C.G., R.A.v.S., and N.A.J.M.S. analyzed data; and E.G.V., Q.S., M.T., P.J.K., W.W.C.G., R.A.v.S., and N.A.J.M.S. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission. R.G. is a guest editor invited by the Editorial Board.

{dagger}To whom correspondence should be addressed. E-mail: e.g.vrieling{at}rug.nl

© 2007 by The National Academy of Sciences of the USA


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