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A model for the effects of germanium on silica biomineralization in choanoflagellates.

Published version
Peer-reviewed

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Authors

Chappell, Helen 
Ratcliffe, Sarah 
Goldstein, Raymond E 

Abstract

Silica biomineralization is a widespread phenomenon of major biotechnological interest. Modifying biosilica with substances like germanium (Ge) can confer useful new properties, although exposure to high levels of Ge disrupts normal biosilicification. No clear mechanism explains why this disruption occurs. Here, we study the effect of Ge on loricate choanoflagellates, a group of protists that construct a species-specific extracellular lorica from multiple siliceous costal strips. High Ge exposures were toxic, whereas lower Ge exposures produced cells with incomplete or absent loricae. These effects can be ameliorated by restoring the germanium : silicon ratio, as observed in other biosilicifying organisms. We developed simulations of how Ge interacts with polymerizing silica. In our models, Ge is readily incorporated at the ends of silica forming from silicic acid condensation, but this prevents further silica polymerization. Our 'Ge-capping' model is supported by observations from loricate choanoflagellates. Ge exposure terminates costal strip synthesis and lorica formation, resulting in disruption to cytokinesis and fatal build-up of silicic acid. Applying the Ge-capping model to other siliceous organisms explains the general toxicity of Ge and identifies potential protective responses in metalloid uptake and sensing. This can improve the design of new silica biomaterials, and further our understanding of silicon metabolism.

Description

Keywords

biomineralization, choanoflagellate, first principles modelling, germanium, silicon, toxicity

Journal Title

J R Soc Interface

Conference Name

Journal ISSN

1742-5689
1742-5662

Volume Title

13

Publisher

The Royal Society
Sponsorship
European Research Council (247333)
Higher Education Funding Council for England (Strategic Research Infrastructure Funding), Science and Technology Facilities Council, European Research Council (Advanced Investigator Grant ID: 247333), Wellcome Trust (Senior Investigator Award), Medical Research Council (Grant ID: U105960399, MRC-HNR Career Development Fellowship), European Research Council (Starting Grant ID: 282101 under the European Union’s Seventh Framework Programme (FP7/2007-2013))