Copper Uptake, Intracellular Localization, and Speciation in Marine Microalgae Measured by Synchrotron Radiation X-ray Fluorescence and Absorption Microspectroscopy

Abstract

Metal toxicity to aquatic organisms depends on the speciation of the metal and its binding to the critical receptor site(s) (biotic ligand) of the organism. The intracellular nature of the biotic ligand for Cu in microalgal cells was investigated using the high elemental sensitivity of microprobe synchrotron radiation X-ray fluorescence (SR-XRF) and X-ray absorption near-edge spectroscopy (XANES). The marine microalgae, Ceratoneis closterium, Phaeodactylum tricornutum, and Tetraselmis sp. were selected based on their varying sensitivities to Cu (72-h 50% population growth inhibitions of 8–47 μg Cu/L). Intracellular Cu in control cells was similar for all three species (2.5–3.2 × 10–15 g Cu/cell) and increased 4-fold in C. closterium and Tetraselmis sp. when exposed to copper, but was unchanged in P. tricornutum (72-h exposure to 19, 40, and 40 μg Cu/L, respectively). Whole cell microprobe SR-XRF identified endogenous Cu in the central compartment (cytoplasm) of control (unexposed) cells. After Cu exposure, Cu was colocated with organelles/granules dense in P, S, Ca, and Si and this was clearly evident in thin sections of Tetraselmis sp. XANES indicated coexistence of Cu­(I) and Cu­(II) in control and Cu-exposed cells, with the Cu ligand (e.g., phytochelatin) in P. tricornutum different from that in C. closterium and Tetraselmis sp. This study supports the hypothesis that Cu­(II) is reduced to Cu­(I) and that polyphosphate bodies and phytochelatins play a significant role in the internalization and detoxification of Cu in marine microalgae.

Toxicity, Physiological, and Ultrastructural Effects of Arsenic and Cadmium on the Extremophilic Microalga Chlamydomonas acidophila

“…The high levels of phosphorus detected inside cells in all treatments (see TEM-EDX spectra) also support the role of polyphosphate in metal resistance [27,52]. Moreover, in recent studies by X-ray absorption near edge structure (XANES) spectroscopy in several species of marine microalgae, Cu resistance and bioaccumulation has been associated with poly-phosphate [85]. Glutathione and phytochelatins contain free thiolic groups that can reduce As(V) to As(III) and they can also immobilize both cationic forms.…”

Functional CTR‐type Cu(I) transporters in an oceanic diatom

“…Copper uptake kinetics in marine and freshwater phytoplankton follows a saturation curve as predicted for a carrier‐mediated process (Hill et al ., ; Knauer et al ., ; Croot et al ., ; Adams et al ., ). In some phytoplankton, uptake is biphasic implying that two types of transporters may be involved; one of low and one of high affinity (Knauer et al ., ; Guo et al ., ).…”

Experimental Warming Differentially Influences the Vulnerability of Phototrophic and Heterotrophic Periphytic Communities to Copper Toxicity

“…Copper (Cu) is well representative of the widespread metal pollution of surface waters including rivers and streams in agricultural areas, where it has been widely used as a fungicide and weed-killer in both conventional and organic agriculture ( Serra and Guasch, 2009 ; Provenzano et al, 2010 ). Cu is an essential element for organisms, serving as a cofactor in many enzymatic pathways that catalyze a wide variety of functions including several redox reactions as well as photosynthetic and mitochondrial electron transport ( Ladomersky and Petris, 2015 ; Adams et al, 2016 ). However, high concentrations of Cu are toxic to aquatic life, and thus pose ecotoxicological risks in freshwater ecosystems.…”