Abstract
Diatoms play a significant role in the global carbon cycle through their role in biogenic silica production and the transport of organic matter to the seafloor. Recent work has shown that silicified diatom frustules contain a significant amount of organic matter, and that the proportion of diatom-bound organic matter increases with depth in the water column and sediments. Here, we investigate the association between organic matter and the mineral phase. We used a combination of scanning transmission X-ray microscopy (STXM) and carbon X-ray absorption near-edge structure (XANES) spectroscopy to characterize the distribution and composition of organic matter in frustules of the diatom Cylindrotheca closterium and a biomimetic silica gel. To our knowledge, this study represents the first successful attempt to simultaneously image and obtain chemical information about the organic matter within a diatom frustule using X-ray spectromicroscopy near the carbon edge. Organic carbon, most likely protein, was distributed throughout the frustules and was not removed by harsh chemical treatment. The physical structure of the frustules appeared to be related to the chemical composition of this organic matter, with aromatic or unsaturated carbon being concentrated in the most intricately patterned regions of the frustule. A similar physical and chemical structure was observed in a biomimetic silica gel precipitated spontaneously with polylysine. These results are consistent with the theory that organic constituents of diatom frustules direct silica precipitation and become incorporated within the silica matrix as it forms. The relationship between organic matter composition and silica morphology, the failure of harsh chemical treatments to remove this organic matter, and the spontaneous nature of the co-precipitation of silica and organic matter indicate some chemical interaction between the siliceous and organic components of diatom frustules. Frustule-bound organic matter should therefore be protected from decomposition in the water column or diagenetic alteration in sediments unless the frustule dissolves.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1369-1380 |
| Number of pages | 12 |
| Journal | Deep-Sea Research Part II: Topical Studies in Oceanography |
| Volume | 56 |
| Issue number | 18 |
| DOIs | |
| State | Published - Aug 15 2009 |
Funding
We thank Mirna Lerotic, who was instrumental in developing the statistical tools used in this study and who provided considerable assistance with our data analysis. We also thank Anitra Ingalls, whose research on the preservation of biomineral-bound proteins paved the way for this study. The X-1A scanning transmission X-ray microscope used in this study was developed by the group of Janos Kirz and Chris Jacobsen at Stony Brook University, and the zone plates were developed by Steve Spector and Chris Jacobsen of Stony Brook and Don Tennant of Lucent Technologies Bell Labs. Shelagh Palma of Nicholas Fisher's laboratory provided assistance culturing the diatoms. Bassem Allam and Sue Pawagi provided assistance with light microscopy. Klaus Kemp of Microlife Services prepared the samples for scanning electron microscopy (SEM), and Jim Quinn of Stony Brook University operated the SEM. This study was supported by NSF grants OCE0136370 (C. Lee) and OCE0117062 (R. Aller). This is MSRC contribution number 1353 and MedFlux contribution number 14.
Keywords
- Degradation
- Diatom frustules
- Minerals
- Organic matter
- Preservation
ASJC Scopus subject areas
- Oceanography