title: The mechanisms of detoxification of As(III), dimethylarsinic acid (DMA) and As(V) in the microalga Chlorella vulgaris.
abstract: The response of Chlorella vulgaris when challenged by As(III), As(V) and dimethylarsinic acid (DMA) was assessed through experiments on adsorption, efflux and speciation of arsenic (reduction, oxidation, methylation and chelation with glutathione/phytochelatin [GSH/PC]). Our study indicates that at high concentrations of phosphate (1.62mM of HPO4(2-)), upon exposure to As(V), cells are able to shift towards methylation of As(V) rather than PC formation. Treatment with As(V) caused a moderate decrease in intracellular pH and a strong increase in the concentration of free thiols (GSH). Passive surface adsorption was found to be negligible for living cells exposed to DMA and As(V). However, adsorption of As(III) was observed to be an active process in C. vulgaris, because it did not show saturation at any of the exposure periods. Chelation of As(III) with GS/PC and to a lesser extent hGS/hPC is a major detoxification mechanism employed by C. vulgaris cells when exposed to As(III). The increase of bound As-GS/PC complexes was found to be strongly related to an increase in concentration of As(III) in media. C. vulgaris cells did not produce any As-GS/PC complex when exposed to As(V). This may indicate that a reduction step is needed for As(V) complexation with GSH/PC. C. vulgaris cells formed DMAS(V)-GS upon exposure to DMA independent of the exposure period. As(III) triggers the formation of arsenic complexes with PC and homophytochelatins (hPC) and their compartmentalisation to vacuoles. A conceptual model was devised to explain the mechanisms involving ABCC1/2 transport. The potential of C. vulgaris to bio-remediate arsenic from water appeared to be highly selective and effective without the potential hazard of reducing As(V) to As(III), which is more toxic to humans.
authors.affiliation: Department of Natural Sciences, School of Science and Technology, Middlesex University, The Burroughs, London NW4 4BT, United Kingdom.
authors.forename: L
authors.initials: L
authors.lastname: Pantoja Munoz
authors.affiliation: Department of Natural Sciences, School of Science and Technology, Middlesex University, The Burroughs, London NW4 4BT, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Purchase
authors.affiliation: Department of Natural Sciences, School of Science and Technology, Middlesex University, The Burroughs, London NW4 4BT, United Kingdom.
authors.forename: H
authors.initials: H
authors.lastname: Jones
authors.affiliation: College of Physical Sciences - Chemistry, Trace Element Speciation Laboratory (TESLA), University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Raab
authors.affiliation: College of Physical Sciences - Chemistry, Trace Element Speciation Laboratory (TESLA), University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Urgast
authors.affiliation: College of Physical Sciences - Chemistry, Trace Element Speciation Laboratory (TESLA), University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, United Kingdom.
authors.forename: J
authors.initials: J
authors.lastname: Feldmann
authors.affiliation: Department of Natural Sciences, School of Science and Technology, Middlesex University, The Burroughs, London NW4 4BT, United Kingdom. Electronic address: H.Garelick@mdx.ac.uk.
authors.forename: H
authors.initials: H
authors.lastname: Garelick
mesh_terms: D000704:Analysis of Variance; D001151:Arsenic / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D001673:Biodegradation, Environmental; D001692:Biological Transport / Q000187:drug effects; D001711:Biotransformation / Q000502:physiology; D002101:Cacodylic Acid / Q000378:metabolism / Q000633:toxicity*; D048408:Chlorella vulgaris / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D005434:Flow Cytometry; D005978:Glutathione / Q000378:metabolism; D008667:Metalloproteins / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects; D054811:Phytochelatins / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000378:metabolism / Q000633:toxicity*
chemical_list: D008667:Metalloproteins; D014874:Water Pollutants, Chemical; C434267:homophytochelatin; D054811:Phytochelatins; D002101:Cacodylic Acid; D005978:Glutathione; D001151:Arsenic
keywords: ABC/MRP; Arsenic; Chlorella vulgaris; Efflux; Flow cytometry; ICP–MS; Intracellular pH; Oxidative stress