Abstract
Morphogenesis of the silica based cell walls of diatoms, a large group of microalgae, is a paradigm for the self-assembly of complex 3D nano- and microscale patterned inorganic materials. In recent years, loss-of-function studies using genetic manipulation were successfully applied for the identification of genes that guide silica morphogenesis in diatoms. These studies revealed that the loss of one gene can affect multiple morphological parameters, and the morphological changes can be rather subtle being blurred by natural variations in morphology even within the same clone. Both factors severely hamper the identification of morphological mutants using subjective by-eye inspection of electron micrographs. Here we have developed automated image analysis for objectively quantifying the morphology of ridge networks and pore densities from numerous electron micrographs of diatom biosilica. This study demonstrated differences in ridge network morphology and pore density in diatoms growing on ammonium rather than nitrate as the sole nitrogen source. Furthermore, it revealed shortcomings in previous by-eye evaluation of the biosilica phenotype of the silicanin-1 knockout mutant. We anticipate that the computational methods established in the present work will be invaluable for unraveling genotype–phenotype correlations in diatom biosilica morphogenesis.
Highlights
Diatoms represent a large group of unicellular, eukaryotic microalgae that biosynthesize silica based cell walls
We focused on the pattern of silica ridges, which are thickenings of the cell wall that appear as a network of dark lines in transmission electron microscopy (TEM) images (Fig. 1)
In the present work we have developed automated image analysis for evaluating the ridge patterns and pore densities from large numbers of TEM images of diatom biosilica
Summary
Diatoms represent a large group of unicellular, eukaryotic microalgae that biosynthesize silica based cell walls. The 3D nano- to microscale architecture of the biosilica is a species specific trait indicating that its morphology is genetically controlled [1]. The intricate and highly regular, hierarchical porous patterns of diatom biosilica are regarded as paradigms for the bottom-up synthesis of mineral based materials under environmentally benign conditions [2,3,4]. Diatom biosilica microparticles have interesting materials properties that can be exploited for a wide range of applications in photonics, chemical sensing, catalysis and drug delivery [5,6,7,8]. The diatom cell wall consists of two halves of identical structures that are arranged in a petri-dish like arrangement. Each theca is composed of a plate- or dome-shaped valve, exhibiting a species specific silica pattern, and
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