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Cadmium toxicity to Microcystis aeruginosa PCC 7806 and its microcystin-lacking mutant.

Huang B, Xu S, Miao AJ, Xiao L, Yang LY - PLoS ONE (2015)

Bottom Line: The adverse effects of microcystin (MC) produced by cyanobacteria have drawn considerable attention from the public.Yet it remains unclear whether MC confers any benefits to the cyanobacteria themselves.Although the inactivation of MC peptide synthetase gene had some nutrient and Cd concentration dependent effects on the parameters above, both cyanobacterial strains showed the same Cd accumulation ability and displayed similar Cd sensitivity.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu Province, China.

ABSTRACT
The adverse effects of microcystin (MC) produced by cyanobacteria have drawn considerable attention from the public. Yet it remains unclear whether MC confers any benefits to the cyanobacteria themselves. One suggested function of MC is complexation, which may influence the bioaccumulation and toxicity of trace metals. To test this hypothesis, we examined Cd toxicity to wild-type Microcystis aeruginosa PCC 7806 (WT) and its MC-lacking mutant (MT) under nutrient-enriched (+NP), phosphorus-limited (-P), and nitrogen-limited (-N) conditions. The accumulation of Cd and the biochemical parameters associated with its detoxification [total phosphorus (TP), inorganic polyphosphate (Poly-P), and glutathione (GSH) in the cells as well as intra- and extra-cellular carbohydrates] were quantified. Although the -P cyanobacteria accumulated less Cd than their +NP and -N counterparts, the different nutrient-conditioned cyanobacteria were similarly inhibited by similar free ion concentration of Cd in the medium ([Cd2+]F). Such good toxicity predictability of [Cd2+]F was ascribed to the synchronous decrease in the intracellular concentrations of Cd and TP. Nevertheless, Cd toxicity was still determined by the intracellular Cd to phosphorus ratio (Cd/P), in accordance with what has been reported in the literature. On the other hand, the concentrations of TP, Poly-P, and carbohydrates went up, but GSH concentration dropped down with the enhancement of [Cd2+]F, indicating their association with Cd detoxification. Although the inactivation of MC peptide synthetase gene had some nutrient and Cd concentration dependent effects on the parameters above, both cyanobacterial strains showed the same Cd accumulation ability and displayed similar Cd sensitivity. These results suggest that MC cannot affect metal toxicity either by regulating metal accumulation or by altering the detoxification ability of the cyanobacteria. Other possible functions of MC need to be further investigated.

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Variation of (a) intracellular Cd concentration ([Cd]intra) and (b) intracellular Cd to phosphorus ratio (Cd/P) with free Cd ion concentration of the experimental media ([Cd2+]F, 1.00×10-13—1.21×10-8 M) in the nutrient-enriched (+NP, circle), phosphorus-limited (-P, star), and nitrogen-limited (-N, triangle) toxicity tests for Microcystis aeruginosa PCC 7806 (WT, filled symbols) and its MC-lacking mutant (MT, open symbols).Dashed lines are the simulation of the positive relationship between [Cd2+]F and [Cd]intra or Cd/P by the Freundlich isotherm. Data are mean ± standard error (n = 2)
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pone.0116659.g001: Variation of (a) intracellular Cd concentration ([Cd]intra) and (b) intracellular Cd to phosphorus ratio (Cd/P) with free Cd ion concentration of the experimental media ([Cd2+]F, 1.00×10-13—1.21×10-8 M) in the nutrient-enriched (+NP, circle), phosphorus-limited (-P, star), and nitrogen-limited (-N, triangle) toxicity tests for Microcystis aeruginosa PCC 7806 (WT, filled symbols) and its MC-lacking mutant (MT, open symbols).Dashed lines are the simulation of the positive relationship between [Cd2+]F and [Cd]intra or Cd/P by the Freundlich isotherm. Data are mean ± standard error (n = 2)

Mentions: At the end of each 72-h toxicity test, [Cd]intra went up linearly with [Cd2+]F first in the log-scale (Fig. 1a). Then it leveled off when [Cd2+]F was higher than 3.06×10-10, 1.09×10-9, and 3.15×10-10 mol/L in the +NP,-P, and—N toxicity tests, respectively. Further, Cd bioaccumulation ability of WT and MT was comparable to each other (p > 0.05, two-way ANOVA). Accordingly, [Cd]intra ranged from 3.84×10-7 to 6.54×10-3 pg/μm3 for WT and from 3.61×10-7 to 6.94×10-3 pg/μm3 for MT in the—N toxicity tests. Zhou et al. [25] cultured the same cyanobacterial species in BG-11 with [Cd2+]F of 10-11—10-10 M for 48 h. Assuming the cell volume of this cyanobacterium is 25 μm3, its [Cd]intra ranges from 1.72×10-4 to 7.84×10-4 pg/μm3, similar to what we found (1.89×10-5—4.87×10-4 pg/μm3) herein.


Cadmium toxicity to Microcystis aeruginosa PCC 7806 and its microcystin-lacking mutant.

Huang B, Xu S, Miao AJ, Xiao L, Yang LY - PLoS ONE (2015)

Variation of (a) intracellular Cd concentration ([Cd]intra) and (b) intracellular Cd to phosphorus ratio (Cd/P) with free Cd ion concentration of the experimental media ([Cd2+]F, 1.00×10-13—1.21×10-8 M) in the nutrient-enriched (+NP, circle), phosphorus-limited (-P, star), and nitrogen-limited (-N, triangle) toxicity tests for Microcystis aeruginosa PCC 7806 (WT, filled symbols) and its MC-lacking mutant (MT, open symbols).Dashed lines are the simulation of the positive relationship between [Cd2+]F and [Cd]intra or Cd/P by the Freundlich isotherm. Data are mean ± standard error (n = 2)
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4295860&req=5

pone.0116659.g001: Variation of (a) intracellular Cd concentration ([Cd]intra) and (b) intracellular Cd to phosphorus ratio (Cd/P) with free Cd ion concentration of the experimental media ([Cd2+]F, 1.00×10-13—1.21×10-8 M) in the nutrient-enriched (+NP, circle), phosphorus-limited (-P, star), and nitrogen-limited (-N, triangle) toxicity tests for Microcystis aeruginosa PCC 7806 (WT, filled symbols) and its MC-lacking mutant (MT, open symbols).Dashed lines are the simulation of the positive relationship between [Cd2+]F and [Cd]intra or Cd/P by the Freundlich isotherm. Data are mean ± standard error (n = 2)
Mentions: At the end of each 72-h toxicity test, [Cd]intra went up linearly with [Cd2+]F first in the log-scale (Fig. 1a). Then it leveled off when [Cd2+]F was higher than 3.06×10-10, 1.09×10-9, and 3.15×10-10 mol/L in the +NP,-P, and—N toxicity tests, respectively. Further, Cd bioaccumulation ability of WT and MT was comparable to each other (p > 0.05, two-way ANOVA). Accordingly, [Cd]intra ranged from 3.84×10-7 to 6.54×10-3 pg/μm3 for WT and from 3.61×10-7 to 6.94×10-3 pg/μm3 for MT in the—N toxicity tests. Zhou et al. [25] cultured the same cyanobacterial species in BG-11 with [Cd2+]F of 10-11—10-10 M for 48 h. Assuming the cell volume of this cyanobacterium is 25 μm3, its [Cd]intra ranges from 1.72×10-4 to 7.84×10-4 pg/μm3, similar to what we found (1.89×10-5—4.87×10-4 pg/μm3) herein.

Bottom Line: The adverse effects of microcystin (MC) produced by cyanobacteria have drawn considerable attention from the public.Yet it remains unclear whether MC confers any benefits to the cyanobacteria themselves.Although the inactivation of MC peptide synthetase gene had some nutrient and Cd concentration dependent effects on the parameters above, both cyanobacterial strains showed the same Cd accumulation ability and displayed similar Cd sensitivity.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu Province, China.

ABSTRACT
The adverse effects of microcystin (MC) produced by cyanobacteria have drawn considerable attention from the public. Yet it remains unclear whether MC confers any benefits to the cyanobacteria themselves. One suggested function of MC is complexation, which may influence the bioaccumulation and toxicity of trace metals. To test this hypothesis, we examined Cd toxicity to wild-type Microcystis aeruginosa PCC 7806 (WT) and its MC-lacking mutant (MT) under nutrient-enriched (+NP), phosphorus-limited (-P), and nitrogen-limited (-N) conditions. The accumulation of Cd and the biochemical parameters associated with its detoxification [total phosphorus (TP), inorganic polyphosphate (Poly-P), and glutathione (GSH) in the cells as well as intra- and extra-cellular carbohydrates] were quantified. Although the -P cyanobacteria accumulated less Cd than their +NP and -N counterparts, the different nutrient-conditioned cyanobacteria were similarly inhibited by similar free ion concentration of Cd in the medium ([Cd2+]F). Such good toxicity predictability of [Cd2+]F was ascribed to the synchronous decrease in the intracellular concentrations of Cd and TP. Nevertheless, Cd toxicity was still determined by the intracellular Cd to phosphorus ratio (Cd/P), in accordance with what has been reported in the literature. On the other hand, the concentrations of TP, Poly-P, and carbohydrates went up, but GSH concentration dropped down with the enhancement of [Cd2+]F, indicating their association with Cd detoxification. Although the inactivation of MC peptide synthetase gene had some nutrient and Cd concentration dependent effects on the parameters above, both cyanobacterial strains showed the same Cd accumulation ability and displayed similar Cd sensitivity. These results suggest that MC cannot affect metal toxicity either by regulating metal accumulation or by altering the detoxification ability of the cyanobacteria. Other possible functions of MC need to be further investigated.

Show MeSH
Related in: MedlinePlus