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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 cysteine desulfhydrase 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 7%.
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Figure 4: Effect of cadmium on cysteine desulfhydrase 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 7%.

Mentions: The presence of Cd(II) increased cysteine desulfhydrase activity over that of the metal free control in only one of the three investigated species, Chlamydomonas (Figure 4). However, of the Cd(II) treatments the pre- and simultaneously sulfate fed cells had the highest activity in all species after 48 h (ANOVA, p < 0.05). Under these conditions, Cyanidioschyzon had the highest cysteine desulfhydrase activity after 48 h at 21.5 U/mg protein, followed by Chlamydomonas at 7.8 U/mg protein, and Synechococcus at only 2.5 U/mg protein. Simultaneous metal and sulfate treatments consistently had the second highest final activities in the eukaryotic species, whereas for Synechococcus, it was the simultaneous cysteine treatment. All of the Chlamydomonas and Cyanidioschyzon treatments started with an increase in activity whereas cysteine desulfhydrase activity actually initially decreased in all Synechococcus cultures (Figure 4C) followed by slow recoveries up to 48 h (Figure 4C). In the eukaryotic species, both types of cysteine treatments gave transient increases with peak activities at 6 h followed by decreases in activity. All sulfide treatments resulted in relatively low cysteine desulfhydrase activities.


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 cysteine desulfhydrase 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 7%.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Effect of cadmium on cysteine desulfhydrase 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 7%.
Mentions: The presence of Cd(II) increased cysteine desulfhydrase activity over that of the metal free control in only one of the three investigated species, Chlamydomonas (Figure 4). However, of the Cd(II) treatments the pre- and simultaneously sulfate fed cells had the highest activity in all species after 48 h (ANOVA, p < 0.05). Under these conditions, Cyanidioschyzon had the highest cysteine desulfhydrase activity after 48 h at 21.5 U/mg protein, followed by Chlamydomonas at 7.8 U/mg protein, and Synechococcus at only 2.5 U/mg protein. Simultaneous metal and sulfate treatments consistently had the second highest final activities in the eukaryotic species, whereas for Synechococcus, it was the simultaneous cysteine treatment. All of the Chlamydomonas and Cyanidioschyzon treatments started with an increase in activity whereas cysteine desulfhydrase activity actually initially decreased in all Synechococcus cultures (Figure 4C) followed by slow recoveries up to 48 h (Figure 4C). In the eukaryotic species, both types of cysteine treatments gave transient increases with peak activities at 6 h followed by decreases in activity. All sulfide treatments resulted in relatively low cysteine desulfhydrase activities.

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