Speciation of arsenic in Euglena gracilis cells exposed to As(V).
Euglena gracilis is a photosynthetic eukaryote ubiquitous in arsenic-polluted acid mine drainages and is locally exposed to As(III) and As(V) concentrations up to 250 and 100 mg L(-1), respectively. Here, arsenic speciation in E. graciliswas determined by X-ray absorption spectroscopy and selected (bio)chemical methods on cells grown at nonlimiting phosphate concentrations. Our results suggest the following detoxification scheme: (1) uptake of As(V) from solution in competition with phosphate, (2) intracellular reduction to As(III), (3) complexation by cytoplasmic proteic thiol ligands of low molecular weight, and (4) As(III) export from the cell. However, at As(V) concentrations >100 mg L(-1), growth rate is markedly lowered and As(V) remains mostly unreduced during the extended lag period. Intracellular As(V) is found to be exclusively concentrated in the membrane + nucleus fraction, suggesting that arsenate could substitute for phosphate groups in membranes or in phosphate-containing macromolecules. Thus, arsenic species are partitioned, with As(III)-thiol compounds concentrated in the cytoplasmic proteic pool and As(V)-compounds associated with the membrane + nucleus fraction. The increasing growth delay observed with increasing initial As(V) concentration in the culture medium is proposed to result from the combination of a higher As(V) uptake and limiting intracellular As(V) reduction rate and As(III) export rate. Under high As(V) exposure conditions (200 mg L(-1)) the reduction step is found to be the most limiting step for detoxification.
Miot
Jennyfer
J
Institut de Minéralogie et de Physique des Milieux Condensés and Institut de Physique du Globe de Paris, Universités Paris 6 et Paris 7, UMR 7590, CNRS, 140, rue de Lourmel 75015 Paris, France. miot@impmc.jussieu.fr
Morin
Guillaume
G
Skouri-Panet
Fériel
F
Férard
Céline
C
Poitevin
Antonine
A
Aubry
Emmanuel
E
Ona-Nguema
Georges
G
Juillot
Farid
F
Guyot
François
F
Brown
Gordon E
GE
D000818:Animals; D001151:Arsenic / Q000302:isolation & purification* / Q000633:toxicity*; D001673:Biodegradation, Environmental / Q000187:drug effects; D001692:Biological Transport / Q000187:drug effects; D005056:Euglena gracilis / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D010710:Phosphates / Q000494:pharmacology; D013057:Spectrum Analysis
D010710:Phosphates; D001151:Arsenic