Abstract:
Thermoacidophilic Cyanidiales maintain a competitive edge to inhabit extreme environments suffered from heat, acid, salts, absolute anaerobic, and metals. Due to horizontal gene transfer (HGT) from prokaryotes, Cyanidiales show the prominent metabolic adaptability and acceptance for As and Hg [1]. For example, the oxidation and methylation was found as the detoxification process of highly toxic arsenite for Cyanidiales [2]. Apart from the HGT, there must be newly uncharacterized strategies that have been adopted by Cyanidiales for metal detoxification. Our previous study demonstrated that Cyanidiales are able to withstand the Pb stress via four mechanisms: (1) the defense line provide by polysaccharide, (2) the inorganic Pb-PO4 precipitation, (3) the organic Pb complexation concomitant with the transport to cell vacuoles, and (4) the specific thiol-Pb chelation involved in disruption of protein secondary structures [3]. Noteworthily, individual Cyanidiales species emphasized different Pb tolerance mechanisms, leading to the Pb sorption capacity ranging from 38.2 – 298.4 mg g-1. In terms of mechanisms against toxicity of Cr(VI), different Cyanidiales species could attain the sorption capacities of 168.1 mg g-1 at pH 2.0 and 93.7 mg g-1 at pH 7.0, which were considerably greater than that of other biological materials at comparable pH [4]. Wherein, 89% and 62% of sorbed Cr at pH 2.0 and pH 7.0 was simultaneously reduced to less toxic and mobile Cr(III). In addition to the Cr(VI) that sorbed on algal surfaces, the in vitro Cr(III)-polysaccharide complexes and in vivo Cr(OH)3 attested to the reduction capability of extracellular polymeric substances and thiol groups on cysteine of Cyanidiales. In particular, relatively consistent proportion of Cr(OH)3, irrespective of Cr sorption capacity, might be the key to prompt the Cr sorption capacity. Beyond the metal removal, we expect Cyanidiales could serve as the alternative material for the chemical coagulant in wastewater treatment to reduce the sludge production. Collectively, Cyanidiales show the promise to be the green and sustainable biomaterials for metal remediation, particularly in extreme environmental conditions.
Keywords – Cyanidiales, heavy metal, detoxification, sustainable
References：
[1] A.W. Rossoni, D.C. Price, M. Seger, D. Lyska, P. Lammers, D. Bhattacharya, A.P. Weber, "The genomes of polyextremophilic cyanidiales contain 1% horizontally transferred genes with diverse adaptive functions," eLife, 8, 2019.
[2] J. Qin, C.R. Lehr, C. Yuan, X.C. Le, T.R. McDermott, B.P. Rosen, "Biotransformation of arsenic by a Yellowstone thermoacidophilic eukaryotic alga," PNAS, 106, pp. 5213-5217, 2009.
[3] 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, "Molecular mechanisms for Pb removal by Cyanidiales: a potential biomaterial applied in thermo-acidic conditions," Chem. Eng. J., 401, pp. 125828, 2020.
[4] Y.-L. Cho, Y.-M. Tzou, C.-C. Wang, Y.-C. Lee, L.C. Hsu, S.-L. Liu, A. Assakinah, Y.-H. Chen, Y.-T. Liu, J. Rinklebe, "Removal and Concurrent Reduction of Cr(Vi) by Thermoacidophilic Cyanidiales: A Novel Extreme Biomaterial Enlightened for Acidic and Neutral Conditions," Available at SSRN 4176023, 2022.