Aerobic transformation of zinc into metal sulfide by photosynthetic microorganisms

Abstract

Industrial activity over the last two centuries has increased heavy metal contamination worldwide, leading to greater human exposure. Zinc is particularly common in industrial effluents and although an essential nutrient, it is highly toxic at elevated concentrations. Photoautotrophic microbes hold promise for heavy metal bioremediation applications because of their ease of culture and their ability to produce sulfide through metabolic processes that in turn are known to complex with the metal ion, Hg(II). The green alga Chlamydomonas reinhardtii, the red alga Cyanidioschyzon merolae, and the cyanobacterium Synechococcus leopoliensis were all able to synthesize sulfide and form zinc sulfide when exposed to Zn(II). Supplementation of their respective media with sulfite and cysteine had deleterious effects on growth, although ZnS still formed in Cyanidioschyzon cells to the same extent as in unsupplemented cells. The simultaneous addition of sulfate and Zn(II) had similar effects to that of Zn(II) alone in all three species, whereas supplying sulfate prior to exposure to Zn(II) enhanced metal sulfide production. The coupled activities of serine acetyltransferase and O-acetylserine(thiol)lyase (SAT/OASTL) did not increase significantly in response to conditions in which enhanced ZnS formation occurred; sulfate added prior to and simultaneously with Zn(II). However, even low activity could provide sufficient sulfate assimilation over this relatively long-term study. Because the extractable activity of cysteine desulfhydrase was elevated in cells that produced higher amounts of zinc sulfide, cysteine is the probable source of the sulfide in this aerobic process.

Highly-defective nanocrystals of ZnS formed via dissimilatory bacterial sulfate reduction: A comparative study with their abiogenic analogues

“…Among the efforts to synthesize metal sulfide nanostructures of specific physicochemical properties, the biological pathways via microbial sulfate-reduction are gaining noticeable traction being less energy-intensive and eco-friendly. To date, a variety of microorganisms including bacteria, algae, yeasts, and fungi have been, or are being, tested for the ability to synthesize metal sulfide nanoparticles (Bai et al, 2006;Mandal et al, 2006;Zhou et al, 2010;da Costa et al, 2012;Duran and Seabra, 2012;Hazra et al, 2012;Edwards et al, 2013;Miradeh et al, 2013;Su et al, 2013;Villa-Gomez et al, 2013;Mala and Rose, 2014;Moon et al, 2014).…”

Formation of Mercury Sulfide from Hg(II)–Thiolate Complexes in Natural Organic Matter

“…Sulfide can be produced from aqueous sulfate by dissimilatory sulfatereducing microbes in the laboratory and field, 58,59 and enzymatically from intracellular cysteine by photosynthetic aerobic microorganisms exposed to high levels of sulfate and trace metals in free ionic form in the laboratory. 60,61 Our experimental findings indicate that neither microbial process is needed to nucleate mercury sulfide. Instead, mercury(II)−thiol sulfur complexes in natural organic matter can react to form the solid.…”

Phytoremediation of Heavy Metals: The Use of Green Approaches to Clean the Environment

“…Heavy metals are only transformed from one oxidation state or organic complex to another. Microorganisms can be used for the bioremediation of metals as they reduce metals in their detoxifi cation mechanism (Garbisu and Alkorta 2001 ;Edwards et al 2013 ).…”