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Aerobic transformation of cadmium through metal sulfide biosynthesis in photosynthetic microorganisms.

Edwards CD, Beatty JC, Loiselle JB, Vlassov KA, Lefebvre DD - BMC Microbiol. (2013)

Bottom Line: In general, conditions that increased cadmium sulfide production also resulted in elevated cysteine desulfhydrase activities, strongly suggesting that cysteine is the direct source of sulfur for CdS synthesis.Cadmium(II) tolerance and CdS formation were significantly enhanced by sulfate supplementation, thus indicating that algae and cyanobacteria can produce CdS in a manner similar to that of HgS.However, the enhanced activity of cysteine desulfhydrase indicates that it is instrumental in the provision of H2S for aerobic CdS biosynthesis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, Queen's University, Kingston, ON, Canada.

ABSTRACT

Background: Cadmium is a non-essential metal that is toxic because of its interference with essential metals such as iron, calcium and zinc causing numerous detrimental metabolic and cellular effects. The amount of this metal in the environment has increased dramatically since the advent of the industrial age as a result of mining activities, the use of fertilizers and sewage sludge in farming, and discharges from manufacturing activities. The metal bioremediation utility of phototrophic microbes has been demonstrated through their ability to detoxify Hg(II) into HgS under aerobic conditions. Metal sulfides are generally very insoluble and therefore, biologically unavailable.

Results: When Cd(II) was exposed to cells it was bioconverted into CdS by the green alga Chlamydomonas reinhardtii, the red alga Cyanidioschyzon merolae, and the cyanobacterium, Synechoccocus leopoliensis. Supplementation of the two eukaryotic algae with extra sulfate, but not sulfite or cysteine, increased their cadmium tolerances as well as their abilities to produce CdS, indicating an involvement of sulfate assimilation in the detoxification process. However, the combined activities of extracted serine acetyl-transferase (SAT) and O-acetylserine(thiol)lyase (OASTL) used to monitor sulfate assimilation, was not significantly elevated during cell treatments that favored sulfide biosynthesis. It is possible that the prolonged incubation of the experiments occurring over two days could have compensated for the low rates of sulfate assimilation. This was also the case for S. leopoliensis where sulfite and cysteine as well as sulfate supplementation enhanced CdS synthesis. In general, conditions that increased cadmium sulfide production also resulted in elevated cysteine desulfhydrase activities, strongly suggesting that cysteine is the direct source of sulfur for CdS synthesis.

Conclusions: Cadmium(II) tolerance and CdS formation were significantly enhanced by sulfate supplementation, thus indicating that algae and cyanobacteria can produce CdS in a manner similar to that of HgS. Significant increases in sulfate assimilation as measured by SAT-OASTL activity were not detected. However, the enhanced activity of cysteine desulfhydrase indicates that it is instrumental in the provision of H2S for aerobic CdS biosynthesis.

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Effect of cadmium on coupled serine acetyl-transferase and O-acetylserine(thiol)lyase activity in Chlamydomonas reinhardtii (A), Cyanidioschyzon merolae (B), and Synechococcus leopoliensis (C) exposed to 100, 100, and 2 μM Cd(II), respectively, when supplemented with sulfur containing compounds. No added Cd(II) (), Cd(II) alone (), and Cd(II) with the following additions; sulfate (), prefed sulfate plus sulfate (), sulfite (), prefed sulfite plus sulfite (), cysteine (), and prefed cysteine plus cysteine (). Means are presented (n = 4). SE always less than 6%.
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Figure 3: Effect of cadmium on coupled serine acetyl-transferase and O-acetylserine(thiol)lyase activity in Chlamydomonas reinhardtii (A), Cyanidioschyzon merolae (B), and Synechococcus leopoliensis (C) exposed to 100, 100, and 2 μM Cd(II), respectively, when supplemented with sulfur containing compounds. No added Cd(II) (), Cd(II) alone (), and Cd(II) with the following additions; sulfate (), prefed sulfate plus sulfate (), sulfite (), prefed sulfite plus sulfite (), cysteine (), and prefed cysteine plus cysteine (). Means are presented (n = 4). SE always less than 6%.

Mentions: Each species had significantly different initial SAT/OASTL activities under control conditions (ANOVA, p < 0.05; Figure 3). Exposure to Cd(II) enhanced the activity of coupled SAT and OASTL over controls with no added metal after 48 hrs to 2.0, 1.7, and 3.2 fold in Chlamydomonas (Figure 3A), Cyanidioschyzon (Figure 3B), and Synechococcus (Figure 3C), respectively. This treatment also resulted in the highest enzyme activities in each of the species. The only other Cd(II) treatments that were higher than the controls in all three species were the simultaneously sulfate fed, and the pre- and simultaneously sulfite fed cells. The pre- and simultaneously cysteine-fed Chlamydomonas and Synechococcus had the lowest activities (ANOVA, p < 0.05), although this was not the case for Cyanidioschyzon. In the latter species the treatments with the lowest activities did not differ from the control, and the pre- and simultaneously cysteine-fed cells were significantly different from the control (ANOVA, p < 0.05).


Aerobic transformation of cadmium through metal sulfide biosynthesis in photosynthetic microorganisms.

Edwards CD, Beatty JC, Loiselle JB, Vlassov KA, Lefebvre DD - BMC Microbiol. (2013)

Effect of cadmium on coupled serine acetyl-transferase and O-acetylserine(thiol)lyase activity in Chlamydomonas reinhardtii (A), Cyanidioschyzon merolae (B), and Synechococcus leopoliensis (C) exposed to 100, 100, and 2 μM Cd(II), respectively, when supplemented with sulfur containing compounds. No added Cd(II) (), Cd(II) alone (), and Cd(II) with the following additions; sulfate (), prefed sulfate plus sulfate (), sulfite (), prefed sulfite plus sulfite (), cysteine (), and prefed cysteine plus cysteine (). Means are presented (n = 4). SE always less than 6%.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750252&req=5

Figure 3: Effect of cadmium on coupled serine acetyl-transferase and O-acetylserine(thiol)lyase activity in Chlamydomonas reinhardtii (A), Cyanidioschyzon merolae (B), and Synechococcus leopoliensis (C) exposed to 100, 100, and 2 μM Cd(II), respectively, when supplemented with sulfur containing compounds. No added Cd(II) (), Cd(II) alone (), and Cd(II) with the following additions; sulfate (), prefed sulfate plus sulfate (), sulfite (), prefed sulfite plus sulfite (), cysteine (), and prefed cysteine plus cysteine (). Means are presented (n = 4). SE always less than 6%.
Mentions: Each species had significantly different initial SAT/OASTL activities under control conditions (ANOVA, p < 0.05; Figure 3). Exposure to Cd(II) enhanced the activity of coupled SAT and OASTL over controls with no added metal after 48 hrs to 2.0, 1.7, and 3.2 fold in Chlamydomonas (Figure 3A), Cyanidioschyzon (Figure 3B), and Synechococcus (Figure 3C), respectively. This treatment also resulted in the highest enzyme activities in each of the species. The only other Cd(II) treatments that were higher than the controls in all three species were the simultaneously sulfate fed, and the pre- and simultaneously sulfite fed cells. The pre- and simultaneously cysteine-fed Chlamydomonas and Synechococcus had the lowest activities (ANOVA, p < 0.05), although this was not the case for Cyanidioschyzon. In the latter species the treatments with the lowest activities did not differ from the control, and the pre- and simultaneously cysteine-fed cells were significantly different from the control (ANOVA, p < 0.05).

Bottom Line: In general, conditions that increased cadmium sulfide production also resulted in elevated cysteine desulfhydrase activities, strongly suggesting that cysteine is the direct source of sulfur for CdS synthesis.Cadmium(II) tolerance and CdS formation were significantly enhanced by sulfate supplementation, thus indicating that algae and cyanobacteria can produce CdS in a manner similar to that of HgS.However, the enhanced activity of cysteine desulfhydrase indicates that it is instrumental in the provision of H2S for aerobic CdS biosynthesis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, Queen's University, Kingston, ON, Canada.

ABSTRACT

Background: Cadmium is a non-essential metal that is toxic because of its interference with essential metals such as iron, calcium and zinc causing numerous detrimental metabolic and cellular effects. The amount of this metal in the environment has increased dramatically since the advent of the industrial age as a result of mining activities, the use of fertilizers and sewage sludge in farming, and discharges from manufacturing activities. The metal bioremediation utility of phototrophic microbes has been demonstrated through their ability to detoxify Hg(II) into HgS under aerobic conditions. Metal sulfides are generally very insoluble and therefore, biologically unavailable.

Results: When Cd(II) was exposed to cells it was bioconverted into CdS by the green alga Chlamydomonas reinhardtii, the red alga Cyanidioschyzon merolae, and the cyanobacterium, Synechoccocus leopoliensis. Supplementation of the two eukaryotic algae with extra sulfate, but not sulfite or cysteine, increased their cadmium tolerances as well as their abilities to produce CdS, indicating an involvement of sulfate assimilation in the detoxification process. However, the combined activities of extracted serine acetyl-transferase (SAT) and O-acetylserine(thiol)lyase (OASTL) used to monitor sulfate assimilation, was not significantly elevated during cell treatments that favored sulfide biosynthesis. It is possible that the prolonged incubation of the experiments occurring over two days could have compensated for the low rates of sulfate assimilation. This was also the case for S. leopoliensis where sulfite and cysteine as well as sulfate supplementation enhanced CdS synthesis. In general, conditions that increased cadmium sulfide production also resulted in elevated cysteine desulfhydrase activities, strongly suggesting that cysteine is the direct source of sulfur for CdS synthesis.

Conclusions: Cadmium(II) tolerance and CdS formation were significantly enhanced by sulfate supplementation, thus indicating that algae and cyanobacteria can produce CdS in a manner similar to that of HgS. Significant increases in sulfate assimilation as measured by SAT-OASTL activity were not detected. However, the enhanced activity of cysteine desulfhydrase indicates that it is instrumental in the provision of H2S for aerobic CdS biosynthesis.

Show MeSH
Related in: MedlinePlus