Solid-state NMR spectroscopic studies of 13C,15N,29Si-enriched biosilica from the marine diatom Cyclotella cryptica

Abstract

Diatoms are algae producing micro- and nano-structured cell walls mainly containing amorphous silica. The shape and patterning of these cell walls is species-specific. Herein, the biosilica of Cyclotella cryptica, a centric marine diatom with a massive organic matrix, is studied. Solid-state NMR spectroscopy is applied to gain deeper insight into the interactions at the organic–inorganic interface of the cell walls. The various organic compounds like polysaccharides as well as proteins and long-chain polyamines (LCPAs) are detected by observation of heteronuclei like 13C and 15N whereas the silica phase is studied using 29Si NMR spectroscopy. The sensitivity of the NMR experiments is strongly enhanced by isotope-labeling of the diatoms during cultivation with 13C, 15N and 29Si. The presence of two different chitin species in the biosilica is demonstrated. This observation is supported by a monosaccharide analysis of the silica-associated organic matrix where a high amount of glucosamine is found. Moreover, the Rotational Echo Double Resonance (REDOR) experiment provides distance information for heteronuclear spins. 13C{29Si} REDOR experiments reveal proximities between different organic compounds and the silica phase. The closest contacts between silica and organic compounds appear for different signals in the 13C-chemical shift range of 40–60 ppm, the typical range for LCPAs.

Solid-State NMR Investigations of Extracellular Matrixes and Cell Walls of Algae, Bacteria, Fungi, and Plants

“…The ensuing low sensitivity makes it difficult to characterize silica in cellular systems. Using isotopically enriched 29 SiO 2 , NaH 13 CO 3 , and Na 15 NO 3 , Tesson et al 507 and Kolbe et al 515 produced labeled samples of T. pseudonana and Cyclotella cryptica diatoms. The combination of 31 P, 13 C, 15 N, and 29 Si ssNMR methods allowed the identification of signals from carbohydrates, nucleic acids, biosilica, lipids, and proteins using a single sample (Figure 17C,D).…”

“…520 Indeed, most recent works report both surface 507 and interior 512 chitin molecules that can be important within the cell wall of T. pseudonana. 13 C labeling allowed the identification of αand βchitin allomorphs in C. cryptica 515 and T. pseudonana, 512 respectively associated with silica and structural chitin. Finally, glucoronomannan was found to be of high significance to cellwall biogenesis in some diatoms.…”

“…442 The contacts between biosilica and organic molecules in Thalassoria pseudonana and Cyclotella cryptica cell walls have been assessed using both { 1 H}− 13 C− 29 Si double CP-based HETCOR and 13 C{ 29 Si} REDOR expriments. 515,522 Contacts were observed between the 29 Si in silica and the 13 C sites of longchain polyamine (LPA) and chitin.…”

Comparison of Biogenic Amorphous Silicas Found in Common Horsetail and Oat Husk With Synthetic Amorphous Silicas

“…As noted earlier, amorphous silica can be found in the skeletons of algae (diatoms) (19)(20)(21)(22)(23)(24)(25)(26), even in deep-sea sponges and molluscs (27).…”

A review on diatom biosilicification and their adaptive ability to uptake other metals into their frustules for potential application in bone repair

“…49 Kolbe et al also used similar techniques to gain a better understanding of the organic matrix associated with the silica and found high concentrations of glucosamine, an amino sugar. 50 Although significant progress has been made in this field, these findings would suggest much work is still needed to fully understand the other major molecules involved in diatom biosilica formation.…”