2020同步年報

Life Science 051 (Gm), Cyanidioschyzon merolae (Cm) and Cyanidium cal- darium (Cc), which belong to varied genera. The maximum observed sorption of Pb(II) ions Cc, Cm and Gm were 298.4, 214.0 and 38.2 mg g -1 , respectively. Employing a transmission X-ray microscope (TXM) at TLS 01B1 , the team revealed that the darker shadows along with the cell outline in Gm with sorbed Pb implied that Pb generally distributed around the cell surface ( Fig. 1(b) ). In contrast, TXM images for Cm and Cc with sorbed Pb showed darker shadows that were scattered around the cell ( Figs. 1(d) and 1(f) ), indicating a plausible accumula- tion in vivo for Pb. These significant variations in the tomog- raphy of Cyanidiales upon sorption of Pb(II) ions indicated that alternative mechanisms for Pb tolerance might be adopted by individual Cyanidiale genera. Utilizing X-ray absorption spectra (XAS) at TLS 17C1 and SP 12B1 , the team found that the Pb inventory in all samples was dominated by both inorganic [Pb 5 (PO 4 ) 3 Cl] and or- ganic [Pb-polysaccharide, Pb-thiol peptide and Pb-organic functional group] Pb species. Whereas Pb 5 (PO 4 ) 3 Cl was the major specie on Gm, the proportion of the Pb-organic functional group was the major specie on Cm. Noteworthi- ly, the great proportion of Pb-thiol peptide on Cc plausibly implies a unique mechanism of defence against the toxicity of heavy metals, leading to the greatest capacity of Pb(II) ion sorption on Cc. Fig. 3 : Conceptualization of four mechanisms of Pb retention on Gm, Cm and Cc: the defence line provided by polysaccharide, inorganic Pb-PO 4 precipitation, organic Pb complexation con- comitant with transport to cell vacuoles and specific thiol-Pb chelation involved in disruption of protein secondary structures. [Reproduced from Ref. 1] To determine the changes in functional groups of Cyan- idiales after Pb(II) ion sorption, the team used synchro- tron-based Fourier-transform infrared (FTIR) spectra at TLS 14A1 . Due to the heterogeneous morphology of algae surfaces, changes of the α-helix were normalized to that of a β-strand to obtain accurate trends caused by sorption of the Pb(II) ion. The metallothionein protein that regu- lates metal homeostasis and imparts a defence against heavy-metal toxicity through intracellular sequestration contains N-terminal and C-terminal motifs joined by α-helix and β-strand structures. It is thus reasonable to postulate the α-helix/β-strand ratio as the major indicator responsible for metal stress tolerance in Cyanidiales. These structural changes in the secondary structure of proteins implied the denaturation of existing proteins or the variation in protein distribution during apoptosis. An inverse relation hence indicated the disruption or modification of the α-helix by the Pb stress ( Fig. 2(d) ). Among tested Cyanidiales, Cc showed a unique response for the metal tolerance, wherein the α-helix was prone to unfold as the sorbed Pb increased. Such protein denaturation in vivo agreed with the greatest proportion of unordered structure in the sample of Cc. In summary, Cyanidiales generally perform four mecha- nisms against Pb toxicity ( Fig. 3 ); individual defence re- sponses were highlighted by specific Cyanidiales species. The knowledge provided here could improve the appli- cation of Cyanidiales in environmental remediation as an innovative green technology. (Reported by Yu-Ting Liu, National Chung Hsing University) This report features the work of Yu- Ting Liu and her collaborators pub- lished in Chem. Eng. J. 401 , 125828 (2020). TLS 14A1 BM – IR Microscopy TLS 17C1 W200 – EXAFS TLS 01B1 SWLS – X-ray Microscopy SP 12B1 BM – Materials X-ray Study • IR, TXM, XAS • Environmental and Earth Science, Biological Science, Chemistry Reference 1. Y.-L. Cho, Y.-C. Lee, L.-C. Hsu, C.-C. Wang, P.-C. Chen, S.-L. Liu, H.-Y. Teah, Y.-T. Liu, Y.-M. Tzou, Chem. Eng. J. 401 , 125828 (2020).