title: Effects of nitrogen and phosphorus on arsenite accumulation, oxidation, and toxicity in Chlamydomonas reinhardtii.
abstract: We studied arsenite (iAs(III)) accumulation, oxidation, and toxicity in the freshwater green alga Chlamydomonas reinhardtii under nutrient-enriched (+NP), phosphorus-limited (-P), and nitrogen-limited (-N) conditions. The -P alga (55.1 μM) had a Michaelis constant (Kd) for uptake approximately one tenth of the +NP (419 μM) and -N (501 μM) cells, indicating iAs(III) uptake inhibition by extracellular phosphate. This conclusion was supported by the hyperbolic reduction in iAs(III) uptake rate (V) from 9.2 to 0.8 μmol/g-dw/h when the extracellular phosphate concentration went up from 0 to 250 μM. The maximal iAs(III) uptake rate (Vmax) of the -N alga (24.3 μmol/g-dw/h) was twice as much as that of the +NP (12 μmol/g-dw/h) and -P (8.1 μmol/g-dw/h) cells. It implies that more arsenic transporters were synthesized under the -N condition. Once accumulated, iAs(III) was oxidized and a higher proportion of arsenate (iAs(V)) was observed at lower [As]dis or under nutrient-limited conditions. Nevertheless, iAs(III) oxidation mainly occurred outside the cells with the extent of oxidation reciprocal to [As]dis. Based on the logistic modeling of the concentration-response curves in the +NP, -P, and -N toxicity tests, iAs(III) had an [As]dis-based EC50 of 1763, 13.1, and 1208 μM and an intracellular arsenic concentration based EC50 of 35.6, 28.8, and 195 μmol/g-dw, respectively. Higher iAs(III) toxicity to the -P cells occured because of their increased iAs(III) accumulation, whereas the underlying mechanisms why the -N alga was more tolerant need to be further revealed. Overall, both N and P had remarkable effects on the behavior and effects of iAs(III), which cannot be disregarded in the biogeochemical cycling research of arsenic.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, Jiangsu Province, China.
authors.forename: Ning-Xin
authors.initials: NX
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, Jiangsu Province, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Huang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, Jiangsu Province, China.
authors.forename: Shen
authors.initials: S
authors.lastname: Xu
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, Jiangsu Province, China.
authors.forename: Zhong-Bo
authors.initials: ZB
authors.lastname: Wei
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, Jiangsu Province, China. Electronic address: miaoaj@nju.edu.cn.
authors.forename: Ai-Jun
authors.initials: AJ
authors.lastname: Miao
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, Jiangsu Province, China. Electronic address: ji@nju.edu.cn.
authors.forename: Rong
authors.initials: R
authors.lastname: Ji
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, Jiangsu Province, China.
authors.forename: Liu-Yan
authors.initials: LY
authors.lastname: Yang
mesh_terms: D001149:Arsenates / Q000032:analysis; D001151:Arsenic / Q000378:metabolism; D018053:Arsenites / Q000378:metabolism* / Q000633:toxicity*; D016825:Chlamydomonas reinhardtii / Q000187:drug effects* / Q000378:metabolism*; D016015:Logistic Models; D009584:Nitrogen / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010758:Phosphorus / Q000494:pharmacology; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: D001149:Arsenates; D018053:Arsenites; D014874:Water Pollutants, Chemical; D010758:Phosphorus; C015001:arsenite; D001151:Arsenic; D009584:Nitrogen; C025657:arsenic acid
keywords: Algae; Arsenite; Efflux; Oxidation; Toxicity; Uptake