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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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Cellular MC-LR concentration ([MC-LR]cell, fg/μm3) in treatments A-H of the nutrient-enriched (+NP), phosphorus-limited (-P), and nitrogen-limited (-N) toxicity tests for Microcystis aeruginosa PCC 7806 (WT). Cd concentration in treatments A-H ([Cd]T, 1.00×10-8—9.95×10-6 M; [Cd2+]F, 1.00×10-13—1.21×10-8 M) is listed in Table B of S1 File.Data are mean ± standard error (n = 2)
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pone.0116659.g006: Cellular MC-LR concentration ([MC-LR]cell, fg/μm3) in treatments A-H of the nutrient-enriched (+NP), phosphorus-limited (-P), and nitrogen-limited (-N) toxicity tests for Microcystis aeruginosa PCC 7806 (WT). Cd concentration in treatments A-H ([Cd]T, 1.00×10-8—9.95×10-6 M; [Cd2+]F, 1.00×10-13—1.21×10-8 M) is listed in Table B of S1 File.Data are mean ± standard error (n = 2)

Mentions: Although the adverse effects of MC have drawn considerable attention from the public, its potential function in the cyanobacteria themselves remains largely unknown. In the present study, no MC-LR was detected in MT and [MC-LR]cell of WT stayed constant when [Cd2+]F was low, but went down by as much as 44.1% at higher [Cd2+]F (Fig. 6). As nitrogen was required during the synthesis of MC, [MC-LR]cell of the—N cells was significantly (p < 0.05) lowered. Nevertheless, the—N cyanobacterium displayed similar sensitivity to Cd (EC50 = 1.15×10-10 M), compared to its +NP counterpart (EC50 = 8.96×10-11 M) (Table 1). Although MT doesn’t possess any variant of MC, its EC50 was similar to that of WT under each nutrient condition and both strains also had comparable [Cd]intra. All these phenomena suggest that MC might not have any direct effects on the intracellular complexation or detoxification of Cd. The hypothesis was supported by the study of Fujii et al. [8], where the uptake of both ferric and ferrous iron by M. aeruginosa PCC 7806 remains unchanged when the MC synthesis gene mcyH in this cyanobacterium is inactivated. Our previous study also manifests that 1 mg/L MC does not have any considerable roles in the bioavailability of various metals (Cd, Cu, Zn, and Cr) to the green alga C. reinhardtii [4].


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)

Cellular MC-LR concentration ([MC-LR]cell, fg/μm3) in treatments A-H of the nutrient-enriched (+NP), phosphorus-limited (-P), and nitrogen-limited (-N) toxicity tests for Microcystis aeruginosa PCC 7806 (WT). Cd concentration in treatments A-H ([Cd]T, 1.00×10-8—9.95×10-6 M; [Cd2+]F, 1.00×10-13—1.21×10-8 M) is listed in Table B of S1 File.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.g006: Cellular MC-LR concentration ([MC-LR]cell, fg/μm3) in treatments A-H of the nutrient-enriched (+NP), phosphorus-limited (-P), and nitrogen-limited (-N) toxicity tests for Microcystis aeruginosa PCC 7806 (WT). Cd concentration in treatments A-H ([Cd]T, 1.00×10-8—9.95×10-6 M; [Cd2+]F, 1.00×10-13—1.21×10-8 M) is listed in Table B of S1 File.Data are mean ± standard error (n = 2)
Mentions: Although the adverse effects of MC have drawn considerable attention from the public, its potential function in the cyanobacteria themselves remains largely unknown. In the present study, no MC-LR was detected in MT and [MC-LR]cell of WT stayed constant when [Cd2+]F was low, but went down by as much as 44.1% at higher [Cd2+]F (Fig. 6). As nitrogen was required during the synthesis of MC, [MC-LR]cell of the—N cells was significantly (p < 0.05) lowered. Nevertheless, the—N cyanobacterium displayed similar sensitivity to Cd (EC50 = 1.15×10-10 M), compared to its +NP counterpart (EC50 = 8.96×10-11 M) (Table 1). Although MT doesn’t possess any variant of MC, its EC50 was similar to that of WT under each nutrient condition and both strains also had comparable [Cd]intra. All these phenomena suggest that MC might not have any direct effects on the intracellular complexation or detoxification of Cd. The hypothesis was supported by the study of Fujii et al. [8], where the uptake of both ferric and ferrous iron by M. aeruginosa PCC 7806 remains unchanged when the MC synthesis gene mcyH in this cyanobacterium is inactivated. Our previous study also manifests that 1 mg/L MC does not have any considerable roles in the bioavailability of various metals (Cd, Cu, Zn, and Cr) to the green alga C. reinhardtii [4].

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