NSRRC Activity Report 2023

076 NSRRC ACTIVITY REPORT 2023 Yu-Ting Liu (National Chung Hsing University) and her collaborators recently uncovered the molecular mechanisms of extreme microalgae Cyanidiales in Cr(VI) removal. Cr released from industrial activities poses a significant threat to the ecosystem. It exists in two common valence states: Cr(III) and Cr(VI). Cr(VI) is highly mobile and toxic, posing a significant risk to human health when entering the food chain. To resolve this problem, a biomaterial composed of Cyanidiales was developed. Cyanidiales are red microalgae that thrive in extremely acidic and thermal environments enriched with heavy metals. Cyanidiales have potential use as a biomaterial for Cr(VI) removal as they possess specific genes for metal detoxification. This study is the first to investigate the capacity and associated mechanisms of Cr(VI) sorption on Cyanidiales under both acidic (pH 2.0) and neutral (pH 7.0) conditions. Here, three species (sp.) of Cyanidiales were tested: Cyanidioschyzon sp. (Cm), Cyanidium sp. (Cc), and Galdieria sp. (Gp). The highest sorption capacity of Cr(VI) was found for Gp (93.7 mg g -1 ) at pH 7.0 ( Fig. 1(f) ) and Cc (168.1 mg g -1 ) at pH 2.0 ( Fig. 1(g) ). To uncover the related metal distribution on Cyanidiales, transmission X-ray microscopy (TXM) was conducted at TLS 01B1 . At pH 2.0, where Cyanidiales showed the highest sorbed Cr levels, Cm ( Fig. 1(a) ) and Cc ( Fig. 1(b) ) cells retained relative integrity, whereas Gp ( Fig. 1(c) ) cells experienced damage. At pH 7.0, Cm ( Fig. 1(d) ) experienced a notable decline in membrane integrity, while Gp ( Fig. 1(f) ) displayed fragment-like Cr accumulation scattered along the cell. TXM results ( Figs. 1(a)–1(f) ) confirm Cr retention in Cyanidiales. In addition, diverse cell morphology and Cr distribution under Cr(VI) stress suggest that each Cyanidiales species likely employs different tolerance strategies. To determine the related metal speciation on Cyanidiales, X-ray absorption spectroscopy (XAS) was conducted at TLS 17C1 and TPS 44A1 . For all samples, the Cr species were well-fitted by K 2 Cr 2 O 7 (representing Cr(VI) ion sorbed on cells), Cr(III)-polysaccharide (denoting Cr(III) ion bonded with a polysaccharide), and Cr(OH) 3 (the Cr(III) precipitate) ( Figs. 1(g) and 1(h) ). At pH 2.0 ( Fig. 1(g) ), Cm displayed the highest Cr sorption capacity among the tested Cyanidiales, primarily as Cr(III)-polysaccharide. Cc exhibited the highest dominance of sorbed Cr(VI) (K 2 Cr 2 O 7 ), while Gp retained Cr(VI) and Cr(III)-polysaccharide in comparable proportions. At pH 7.0 ( Fig. 1(h) ), the absence of Cr(OH) 3 was a common feature in Cyanidiales with the highest Cr retention. Despite the reduction and fixation of sorbed Cr(VI) by the polysaccharide, the proportion of Cr(OH) 3 generally declined with increasing sorbed Cr, suggesting cell surfaces as the primary defense against Cr. The consistent presence of Cr(OH) 3 on Cm and Cc at pH 2.0 may contribute to enhanced Cr tolerance and sorption capacity. Chromium(VI) Removal by Extreme Microalgae— Cyanidiales Molecular mechanisms of chromium(VI) removal by Cyanidiales: a novel extreme biomaterial enlightened for acidic and neutral conditions and during eutrophic events. (Reported by Biqing Liang, National Cheng Kung University) This report features the work of Biqing Liang and her collaborators published in Chemosphere 337 , 139357 (2023). TPS 21A X-ray Nanodiffraction TPS 19A High-resolution Powder X-ray Diffraction TLS 01B1 X-ray Microscopy TLS 14A1 IR Microscopy • X-ray Laue Diffraction, High-resolution Powder XRD, X-ray Tomography, IR Spectroscopy • Environmental and Earth Sciences, Chemistry, Materials Science References 1. M.-S. Sader, K. Lewis, G.-A. Soares, R.-Z. LeGeros, Mater. Res-Ibero-Am. J. 16 , 779 (2013). 2. Y. Chen, M. Li, Y. Li, Y. Liu, Y. Chen, H. Li, L. Li, F. Xu, H. Jiang, L. Chen, Bioresour. Technol. 321 , 124413 (2021). 3. C. Zhou, X. Song, Y. Wang, H. Wang, S. Ge, Chemo- sphere 286 , 131810 (2022). 3. T.-T.Qian, Y.-J. Wang, T.-T. Fan, G.-D.Fang, D.-M. Zhou, Sci. Rep. 6 , 33630 (2016). 4. P. P. Biswas, J. Rathod, C.-Y. Chiang, B. Liang, C.-C. Wang, Y.-C. Lee, Y.-C. Chuang, P. C. Loni, W.-H. Chen, S.-L. Wang, Chemosphere 337 , 139357 (2023).