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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 concentration of (a-c) total phosphorus (TP) and (d-f) inorganic polyphosphate (Poly-P) in treatments A-H of the (a, d) nutrient-enriched (+NP), (b, e) phosphorus-limited (-P), and (c, f) nitrogen-limited (-N) toxicity tests for Microcystis aeruginosa PCC 7806 (WT, black bar) and its MC-lacking mutant (MT, white bar).All values were normalized to levels (100% as represented by the dashed lines) detected in the WT strain at the lowest respective Cd concentration (Treatment A). 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.g003: Cellular concentration of (a-c) total phosphorus (TP) and (d-f) inorganic polyphosphate (Poly-P) in treatments A-H of the (a, d) nutrient-enriched (+NP), (b, e) phosphorus-limited (-P), and (c, f) nitrogen-limited (-N) toxicity tests for Microcystis aeruginosa PCC 7806 (WT, black bar) and its MC-lacking mutant (MT, white bar).All values were normalized to levels (100% as represented by the dashed lines) detected in the WT strain at the lowest respective Cd concentration (Treatment A). 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: At the end of each toxicity test, cellular TP concentration was first kept constant, but increased significantly (p < 0.05, two-way ANOVA, Table C in S1 File) at higher [Cd2+]F, even when its value was lowered by one order of magnitude under the—P condition (Fig. 3 and Figure A in S1 File). Consequently, the cellular TP concentration of WT was enhanced by 63.6%, 230.5%, and 358.1% in treatment H, compared to the control treatment of the +NP,-P, and—N toxicity tests, respectively. The stimulative effect of Cd on cellular TP indicates that phosphorus might play an important role in alleviating Cd toxicity to WT and MT. This hypothesis was further supported by our findings that the +NP,-P, and—N cells displayed comparable Cd/P at the same [Cd2+]F regardless of the nutrient conditions and cyanobacterial strain (Fig. 1b). As [Cd2+]F-based EC50s of the six toxicity tests were similar to each other (Table 1), Cd toxicity was still determined by intracellular Cd/P in the present study. Therefore, the good predictability of [Cd2+]F was just attributable to the synchronous decrease of [Cd]intra together with the cellular concentration of TP. Phosphorus association with Cd detoxification may partly explain why WT and MT with comparable cellular concentration of TP at lower levels of Cd had similar sensitivity to Cd. However, the underlying mechanisms why MT showed higher cellular concentration of TP than WT at higher levels of [Cd2+]F (Table C in S1 File), especially under the +NP and—N conditions, need to be further investigated.


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 concentration of (a-c) total phosphorus (TP) and (d-f) inorganic polyphosphate (Poly-P) in treatments A-H of the (a, d) nutrient-enriched (+NP), (b, e) phosphorus-limited (-P), and (c, f) nitrogen-limited (-N) toxicity tests for Microcystis aeruginosa PCC 7806 (WT, black bar) and its MC-lacking mutant (MT, white bar).All values were normalized to levels (100% as represented by the dashed lines) detected in the WT strain at the lowest respective Cd concentration (Treatment A). 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.g003: Cellular concentration of (a-c) total phosphorus (TP) and (d-f) inorganic polyphosphate (Poly-P) in treatments A-H of the (a, d) nutrient-enriched (+NP), (b, e) phosphorus-limited (-P), and (c, f) nitrogen-limited (-N) toxicity tests for Microcystis aeruginosa PCC 7806 (WT, black bar) and its MC-lacking mutant (MT, white bar).All values were normalized to levels (100% as represented by the dashed lines) detected in the WT strain at the lowest respective Cd concentration (Treatment A). 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: At the end of each toxicity test, cellular TP concentration was first kept constant, but increased significantly (p < 0.05, two-way ANOVA, Table C in S1 File) at higher [Cd2+]F, even when its value was lowered by one order of magnitude under the—P condition (Fig. 3 and Figure A in S1 File). Consequently, the cellular TP concentration of WT was enhanced by 63.6%, 230.5%, and 358.1% in treatment H, compared to the control treatment of the +NP,-P, and—N toxicity tests, respectively. The stimulative effect of Cd on cellular TP indicates that phosphorus might play an important role in alleviating Cd toxicity to WT and MT. This hypothesis was further supported by our findings that the +NP,-P, and—N cells displayed comparable Cd/P at the same [Cd2+]F regardless of the nutrient conditions and cyanobacterial strain (Fig. 1b). As [Cd2+]F-based EC50s of the six toxicity tests were similar to each other (Table 1), Cd toxicity was still determined by intracellular Cd/P in the present study. Therefore, the good predictability of [Cd2+]F was just attributable to the synchronous decrease of [Cd]intra together with the cellular concentration of TP. Phosphorus association with Cd detoxification may partly explain why WT and MT with comparable cellular concentration of TP at lower levels of Cd had similar sensitivity to Cd. However, the underlying mechanisms why MT showed higher cellular concentration of TP than WT at higher levels of [Cd2+]F (Table C in S1 File), especially under the +NP and—N conditions, need to be further investigated.

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