A group of US researchers reported results obtained by coupled micro X-ray fluorescence (µXRF) and X-ray absorption near-edge structure (XANES) for determining the presence of specific sulfur species in coral tissues at high spatial resolution.
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 distributioin is needed. Sulfur (S) is omnipresent as an essential element for life, as it is part of organosulfur compounds such as amino acids (cysteine, methionine) and as a cofactor in proteins such as glutathione disulfide. Identifying and mapping the wide range of sulfur species within complex
biological structures presents a challenge for understanding the
distribution of important biomolecules.
In corals, sulfur is present in both the living tissues and nonliving skeletal components as both organic and inorganic phases. Thus, sulfur 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 dimethylsulfoniopropionate (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 sulfur 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 sulfur species components and distinguish different species and distributions of sulfur 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 sulfur species, such as glutathione disulfide, 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 sulfate likely in the form of adsorbed sulfate.
The authors envision that such combined techniques could be applied for mapping metal species with different energy beamlines 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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last time modified: November 9, 2018