Molecular mechanisms for Pb removal by Cyanidiales: a potential biomaterial applied in thermo-acidic conditions

Abstract

Thermoacidophilic Cyanidiales are capable to survive in extreme environments (20–56 °C; pH 0.5–5.0) with concentrated metals, allowing them to serve as promising green materials applied in metal remediation. It is the first attempt to determine the capacity and related mechanisms for Pb(II) ions sorption on three Cyanidiales genera: Galdieria maximum (Gm), Cyanidioschyzon merolae (Cm), and Cyanidium caldarium (Cc) in relation to changes in Pb speciation obtained from Pb LIII-edge X-ray absorption, organic functional groups, and protein secondary structures derived from synchrotron-based Fourier-transform infrared spectroscopy. Three-dimensional images of Cyanidiales were collected using Transmission X-ray microscopy. Lead tolerance on Cyanidiales was modulated according to four mechanisms: the defense line provide by polysaccharide, the inorganic Pb-PO4 precipitation, the organic Pb complexation concomitant with the transport to cell vacuoles, and the specific thiol-Pb chelation involved in disruption of protein secondary structures. Despite Cyanidiales generally performed all mechanisms against Pb toxicity, individual defense responses were highlighted by specific Cyanidiales species. The redistribution of Pb-polysaccharide species and inorganic Pb-PO4 precipitates toward organic complexation promoted Pb(II) ions sorption capacity of Cyanidiales, accounting for the almost eight-time-greater sorbed Pb (298.4 mg g−1) on Cc in comparison to Gm. The knowledge provided here could improve the application of the Cyanidiales in environmental remediation as an innovative green technology.