title: Zinc toxicity to the alga Pseudokirchneriella subcapitata decreases under phosphate limiting growth conditions.
abstract: Previous studies have suggested that phosphorus (P) deficiency can increase the sensitivity of microalgae to toxic trace metals, potentially due to reduced metal detoxification at low cell P quota. The existing evidence is, however, inconsistent. This study was set up to determine the combined effects of zinc (Zn) and P supplies on Zn and P bioaccumulation and growth of the green microalgae Pseudokirchneriella subcapitata. Zinc toxicity was investigated in (i) a 24h growth rate assay with cells varying in initial cell P quota (0.5-1.7% P on cell dry weight) with no supplemental P during Zn exposure (Expt. 1) and in (ii) a 48h growth assay initiated with cells at the end of a 14-days steady state culture at three P addition rates (RARs) between 0.8 and 1.6day(-1) (Expt.2). The solution Zn concentrations required to reduce final cell density by 10% relative to control (EbC10) were 5-fold (Expt.1) or 2-fold (Expt.2) lower at the highest P supply than at the lowest P supply, i.e. Zn was more toxic at higher P supply, in contrast with the suggestions from previous studies. Cell P quota increased with increasing Zn in the exposure solution (Expt.2), thereby partially overcoming P deficiency under moderate Zn toxicity compared to low Zn exposure. Similarly, cell Zn increased with increasing P supply, potentially induced by Zn-P complexation or precipitation inside the cell. A dynamic growth model accounting for effects of external Zn and internal P on the specific growth rate was calibrated to all data. This model shows that the effect of solution Zn on specific growth rate (ErC50) was statistically unaffected by cell P quota. In contrast, this model predicts that the EbC10 (i.e. EC10 based on cell numbers) varies with P supply because cell P depends on external P and Zn. Moreover, scenario analysis predicts even contrasting trends of the EbC10 with increasing P supply depending on the duration of the growth assay and the P supply scenario. Our data at two experimental scenarios and the prediction under various relevant scenarios suggest a weaker effect of secondary stress factor (Zn) when nutrient deficiency (first stress factor) is prevailing.
authors: Division of Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium. Electronic address: chuan.gao@ees.kuleuven.be.
authors: C
authors: C
authors: Gao
authors: Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, 9000 Gent, Belgium.
authors: K A C
authors: KAC
authors: De Schamphelaere
authors: Division of Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium.
authors: E
authors: E
authors: Smolders
mesh_terms: D000460:Chlorophyta / Q000187:drug effects*; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism; D014131:Trace Elements / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000633:toxicity*; D015032:Zinc / Q000633:toxicity*
chemical_list: D010710:Phosphates; D014131:Trace Elements; D014874:Water Pollutants, Chemical; D015032:Zinc
keywords: Algae; Exponential addition rate; Solution Zn toxicity; Three-dimensional model; Zn–P interaction