Accumulation and bio-oxidation of arsenite mediated by thermoacidophilic Cyanidiales: innate potential biomaterials toward arsenic remediation.

Addressing geogenic and anthropogenic arsenic (As) pollution is critical for environmental health. This study explored arsenite [As(III)] removal using Cyanidiales, particularly Cyanidium caldarium (Cc) and Galdieria partita (Gp), under acidic to neutral pH, and determined As(III) detoxification mechanisms in relation to As speciation and protein secondary structure in Cyanidiales. Regarding As(III) sorption amounts, Cc outperformed Gp, reaching 83.2 mg g-1 of removal at pH 5.0. Wherein, 23.5 % of sorbed As on Cc presented as arsenate [As(V)] complexation with polysaccharides, alongside other predominant species including As(III)-cysteine (41.2 %) and As(III)-polysaccharides (35.3 %) complexes. This suggested that As(III) was directly transported into cells, rather than As(V). Coupled with the formation of As(III)-cysteine complexes within cells, these mechanisms may be key to efficiently accumulating As(III) in Cyanidiales during the 6-h incubation. These results highlight the potential of Cyanidiales for sustainable As(III) remediation and provide new insights into managing As(III) toxicity.

Removal and concurrent reduction of Cr(VI) by thermoacidophilic Cyanidiales: a novel extreme biomaterial enlightened for acidic and neutral conditions.

Thermoacidophilic Cyanidiales maintain a competitive edge in inhabiting extreme environments enriched with metals. Here, species of Cyanidioschyzon merolae (Cm), Cyanidium caldarium (Cc), and Galdieria partita (Gp) were exploited to remove hexavalent chromium [Cr(VI)]. Cm and Gp could remove 168.1 and 93.7 mg g-1 of Cr(VI) at pH 2.0 and 7.0, respectively, wherein 89% and 62% of sorbed Cr on Cm and Gp occurred as trivalent chromium [Cr(III)]. Apart from surface-sorbed Cr(VI), the in vitro Cr(III) bound with polysaccharide and in vivo chromium(III) hydroxide [Cr(OH)3] attested to the reduction capability of Cyanidiales. The distribution of Cr species varied as a function of sorbed Cr amount, yet a relatively consistent proportion of Cr(OH)3, irrespective of Cr sorption capacity, was found only on Cm and Cc at pH 2.0. In conjunction with TXM (transmission X-ray microscopy) images that showed less impaired cell integrity and possible intracellular Cr distribution on Cm and Cc at pH 2.0, the in vivo Cr(OH)3 might be the key to promoting the Cr sorption capacity (≥ 152 mg g-1). Cyanidiales are promising candidates for the green and sustainable remediation of Cr(VI) due to their great removal capacity, the spontaneous reduction under oxic conditions, and in vivo accumulation.