Characterization and Localization of Insoluble Organic Matrices Associated with Diatom Cell Walls: Insight into Their Roles during Cell Wall Formation

Benoit Tesson,Mark Hildebrand,Olga A Zabotina

doi:10.1371/journal.pone.0061675

Benoit Tesson, Mark Hildebrand + Show 1 more

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https://doi.org/10.1371/journal.pone.0061675

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Abstract

Organic components associated with diatom cell wall silica are important for the formation, integrity, and function of the cell wall. Polysaccharides are associated with the silica, however their localization, structure, and function remain poorly understood. We used imaging and biochemical approaches to describe in detail characteristics of insoluble organic components associated with the cell wall in 5 different diatom species. Results show that an insoluble organic matrix enriched in mannose, likely the diatotepum, is localized on the proximal surface of the silica cell wall. We did not identify any organic matrix embedded within the silica. We also identified a distinct material consisting of glucose polymer with variable localization depending on the species. In some species this component was directly involved in the morphogenesis of silica structure while in others it appeared to be only a structural component of the cell wall. A novel glucose-rich structure located between daughter cells during division was also identified. This work for the first time correlates the structure, composition, and localization of insoluble organic matrices associated with diatom cell walls. Additionally we identified a novel glucose polymer and characterized its role during silica structure formation.

Highlights

Diatoms are one of the most ecologically successful microalgae and are important global primary producers
In order to isolate the insoluble organic matrix associated with the cell wall of different diatom species, we first boiled the cells in SDS to remove intracellular and soluble cell wall-associated material and dissolved the silica with a mixture of HF/NH4F (Fig. S1)
The insoluble organic matrix associated with the girdle bands was covered with 100 nm wide and 70 nm high nodules, corresponding to the openings of pores in the girdle bands (Fig. 1g and h)

Summary

Introduction

Diatoms are one of the most ecologically successful microalgae and are important global primary producers. The reason for this success is a long standing question and has been the subject of numerous investigations. A distinct feature of diatoms is their cell wall called the frustule, which is made of silica and organic components. The cell wall consists of two halves, the hypotheca and epitheca; each theca consists of structures called valves, linked together by girdle bands which typically encircle the cell. Different roles have been attributed to the silica of the diatom cell wall, several of which could favorably affect diatom growth and productivity [1]

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