Phytochelatin–cadmium–sulfide high‐molecular‐mass complexes of Euglena gracilis

Abstract

High‐molecular‐mass PC complexes (PC‐HMWCs) constituted by phytochelatins (PCs), cadmium and sulfide are synthesized by several organisms after exposure to cadmium. In this study, PC‐HMWCs were isolated from photoheterotrophic Euglena gracilis and purified to homogeneity, resulting in compounds of molecular mass 50–380 kDa depending on the CdCl2 and sulfate concentrations in the culture medium. In contrast with plants and some yeasts, PC‐HMWCs from E. gracilis mainly comprise (57–75%) monothiol molecules (Cys, γ‐glutamylcysteine, GSH) and, to a lesser extent (25–43%), PCs. A similar acid‐soluble thiol compound composition was found in whole cell extracts. The –SH/Cd2+and S2–/Cd2+ ratios found in purified PC‐HMWCs were 1.5 and 1.8, respectively; the (–SH + S2–)/Cd2+ ratio was 3.2. PC‐HMWCs of molecular mass 60 and 100 kDa were also localized inside Percoll‐purified chloroplasts, in which cadmium and PCs were mainly compartmentalized. Cadmium and sulfur‐rich clusters with similar sulfur/cadmium stoichiometries to those of the purified PC‐HMWCs were detected in the chloroplast and throughout the cell by energy dispersive microanalysis and atomic resolution electron microscopy. The presence of PC‐HMWCs in primitive photosynthetic eukaryotes such as the protist, E. gracilis, suggests that their function as the final cadmium‐storage‐inactivation process is widespread. Their particular intracellular localization suggests that chloroplasts may play a major role in the cadmium‐resistance mechanism in organisms lacking a plant‐like vacuole.

Phytochelatins: Peptides Involved in Heavy Metal Detoxification

“…It is an Mg-ATP-dependent glutathione S-conjugate transporter responsible for vacuolar sequestration of GSH-metal complexes, that transport bis (glutathionato) cadmium (Cd-GS 2 ) into vacuoles [19,111], as well as As-GS 3 [112] and Hg-GS 2 [113]. Recently, Mendoza-Cozatl et al [114] showed the presence of PC-HMW complexes in chloroplasts of Euglena gracilis, suggesting role of chloroplast in Cd resistance mechanism in organisms lacking a plant-like vacuole (Fig. 6).…”

Integrated phytobial remediation for sustainable management of arsenic in soil and water

“…Keimowitz et al (2007), showed that this phenomenon could be utilized at landfill and other sites where As mobilization is a problem. While some eukaryotic microbes like Candida glabrata metabolizes extracellular sulfate to sulfide (Thomas and SurdinKerjan, 1997), that acts as an electron donor for As(V) reduction (Rochette et al, 2000), other yeast like Schizosaccharomyces pombe (Dameron and Winge, 1990) and C. glabrata (Krumov et al, 2007) incorporates sulfide to form a more stable, high molecular weight PC-metal-sulfide complex in the vacuole (Kneer and Zenk, 1997;Mendoza-Cozatl et al, 2006). Some microbes (e.g.…”

“…It is known that sulfide present in soil decreases the toxicity of As by creating metal precipitates. Some eukaryotes also have taken this strategy by incorporating sulfide and forming a high molecular weight PC-metal-sulfide precipitation in the vacuole (Mendoza-Cozatl et al, 2006). However in the bacterial kingdom hydrogen sulfide production is only restricted to anaerobic sulfatereducing bacteria that produce H 2 S only under strict anaerobic condition.…”

Homologous cloning, characterization and expression of a new halophyte phytochelatin synthase gene in Suaeda salsa

“…Non-essential heavy metals (e.g., lead, cadmium and mercury) and excessive essential heavy metals (e.g., zinc and copper) can have many deleterious eff ects on plants, such as chlorosis, necrosis, accelerated aging, and changes in ionome and hormonal status (Lequeux et al, 2010;Pandey and Singh, 2012). To detoxify non-essential or excessive essential heavy metals, high-affi nity substances with abundant thiol groups, such as phytochelatins (PCs), can be used to chelate, sequestrate and compartmentalize heavy metals (Mendoza-Cózatl et al, 2006).…”