Aerobic transformation of cadmium through metal sulfide biosynthesis in photosynthetic microorganisms

Abstract

BackgroundCadmium 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.ResultsWhen 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.ConclusionsCadmium(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.

Single-enzyme biomineralization of cadmium sulfide nanocrystals with controlled optical properties

“…In addition, the purified smCSE enzyme, by itself, is capable of aqueous phase synthesis of CdS nanocrystals directly from cadmium acetate and L-cysteine. The resulting CdS nanocrystals are within the quantum confined size range and display optoelectronic properties analogous to those previously described for cell-based or chemically synthesized CdS nanocrystals (21-23, 32, 34-37 (33,(38)(39)(40)(41)(42) and suggested that H 2 S generation from CSE was the primary driver for CdS precipitation. To determine whether the putative CSE identified from S. maltophilia (smCSE) was capable of H 2 S generation from L-cysteine, smCSE was heterologously overexpressed and purified from Escherichia coli and the intrinsic kinetics of L-cysteine turnover to H 2 S measured (described in SI Appendix, SI Materials and Methods).…”

Effect of Metals, Metalloids and Metallic Nanoparticles on Microalgae Growth and Industrial Product Biosynthesis: A Review

“…In another study, a 10-fold increase in SO 4 2− supply resulted in a Chlamydomonas reinhardtii resistance improved by up to 77% towards Cd. Improved Chlamydomonas resistance was accompanied with an increased activity of cysteine desulfhydrase, an enzyme responsible for the cleavage of cysteine into pyruvate, NH 3 and sulfide, the latter one reported to react with Cd to form CdS [ 181 ].…”

Baicalein ameliorates cadmium-induced hepatic and renal oxidative damage in rats

“…They were found in each range of advanced consumerism and heedful or accidental permit, increased the exposure (Dhanalakshmi and Gawdaman, 2013). Cadmium (Cd) is an important heavy metal, which is discharged into nature by the mining and smelting operations of cadmium, lead, zinc and copper, the use of phosphate fertilizer, and sewage sludge, burning of metropolitan waste (Edwards et al, 2013). People are exposed to Cd from water, rice, potato, tobacco, soil, sleek seeds, root and leaf of vegetables which were polluted by Cd (Nisha et al, 2009;Sakr et al, 2015).…”