Imaging and Identification of Sulphur Species within Corals by X-ray Spectroscopy

Mapping elements in biological tissues with high spatial resolution is a first step to gain information about tissue structure, organization and function. Especially for essential elements being present in many biomolecules, better information than just the elemental distribution is needed. Sulphur (S) is omnipresent as an essential element for life, as it is part of organosulphur compounds such as amino acids (cysteine, methionine) and as a cofactor in proteins such as glutathione disulphide. Identifying and mapping the wide range of sulphur species within complex biological structures presents a challenge for understanding the distribution of important biomolecules.

In corals, sulphur is present in both the living tissues and non-living skeletal components as both organic and inorganic phases. Thus, sulphur in corals has been studied from many perspectives, including characterizing sulfate incorporations into aragonitic skeletons as a way to better understand skeletal growth and to deduce the role of organics in biomineralization mechanisms, quantifying dimethylsulphoniopropionate (DMSP) production in the tissues and endosymbionts as an elevated temperature stress signal during coral bleaching events, and measuring S isotopes in carbonate-associated sulfate (CAS) as a paleoproxy.

The new study:

A group of US researchers now has presented a coupled micro X-ray fluorescence (µXRF) and X-ray absorption near-edge structure (XANES) spectroscopy method for determining the presence of specific sulphur species in coral tissues at high spatial resolution. By using multiple energy stacks and principal component analysis (PCA) of a large spectral database, they were able to more accurately identify sulphur species components and distinguish different species and distributions of sulphur formerly unresolved by previous studies.

Figure: sulfur species distribution in coral tissue/skeleton obtained by combined XRF/XANES spectroscopy [Reprinted (adapted) with permission from (Anal. Chem., 90 (2018) 12559). Copyright 2018 American Chemical Society]

The results from this combined µXRF/XANES mapping revealed that the coral tissues were dominated by more reduced sulphur species, such as glutathione disulphide, cysteine, and sulfoxide, as well as organic sulfate as represented by chondroitin sulfate. Sulfoxide distributions were visually correlated with the presence of zooxanthellae endosymbionts. Coral skeletons were composed primarily of carbonate-associated sulfate (CAS) along with minor contributions from organic sulfate and a separate inorganic sulphate, likely in the form of adsorbed sulphate.

The authors envision that such combined techniques could be applied for mapping metal species with different energy beam lines or using other spatial biological techniques such as fluorescent in situ hybridization probes.

The original study:

Gabriela A. Farfan, Amy Apprill, Samuel M. Webb, Colleen M. Hansel, Coupled X‑ray Fluorescence and X‑ray Absorption Spectroscopy for Microscale Imaging and Identification of Sulfur Species within Tissues and Skeletons of Scleractinian Corals, Anal. Chem., 90 (2018) 12559-12566. DOI: 10.1021/acs.analchem.8b02638

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Yusuke Tamenori, Toshihiro Yoshimura, Nguyen Trong Luan, Hiroshi Hasegawa, Atsushi Suzuki, Hodaka Kawahata, Nozomu Iwasaki, Identification of the chemical form of sulfur compounds in the Japanese pink coral (Corallium elatius) skeleton using μ-XRF/XAS speciation mapping, J. Struct. Biol., 186/2 (2014) 214-223. DOI: 10.1016/j.jsb.2014.04.001

Luan Trong Nguyen, Mohammad Azizur Rahman, Teruya Maki, Yusuke Tamenori, Toshihiro Yoshimura, Atsushi Suzuki, Nozomu Iwasaki, Hiroshi Hasegawa, Distribution of trace element in Japanese red coral Paracorallium japonicum by μ-XRF and sulfur speciation by XANES: Linkage between trace element distribution and growth ring formation, Geochim. Cosmochim. Acta, 127/15 (2014) 1-9. DOI: 10.1016/j.gca.2013.11.023

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Toshihiro Yoshimura, Yusuke Tamenori, Atsushi Suzuki, Rei Nakashima, Nozomu Iwasaki, Hiroshi Hasegawa, Hodaka Kawahata, Element profile and chemical environment of sulfur in a giant clam shell: Insights from μ-XRF and X-ray absorption near-edge structure, Chem. Geol., 352 (2013) 170-175. DOI: 10.1016/j.chemgeo.2013.05.035

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last time modified: September 22, 2024