Bioremediation potential of Cd by transgenic yeast expressing a metallothionein gene from Populus trichocarpa

Abstract

Cadmium (Cd) is an extremely toxic environmental pollutant with high mobility in soils, which can contaminate groundwater, increasing its risk of entering the food chain. Yeast biosorption can be a low-cost and effective method for removing Cd from contaminated aqueous solutions.We transformed wild-type Saccharomyces cerevisiae (WT) with two versions of a Populus trichocarpa gene (PtMT2b) coding for a metallothionein: one with the original sequence (PtMT2b 'C') and the other with a mutated sequence, with an amino acid substitution (C3Y, named here: PtMT2b 'Y'). WT and both transformed yeasts were grown under Cd stress, in agar (0; 10; 20; 50 µM Cd) and liquid medium (0; 10; 20 µM Cd). Yeast growth was assessed visually and by spectrometry OD600. Cd removal from contaminated media and intracellular accumulation were also quantified. PtMT2b 'Y' was also inserted into mutant strains: fet3fet4, zrt1zrt2 and smf1, and grown under Fe-, Zn-and Mn-deficient media, respectively. Yeast strains had similar growth under 0 µM, but differed under 20 µM Cd, the order of tolerance was: WT < PtMT2b 'C' < PtMT2b 'Y', the latter presenting 37% higher growth than the strain with PtMT2b 'C'. It also extracted ~80% of the Cd in solution, and had higher intracellular Cd than WT. Mutant yeasts carrying PtMT2b 'Y' had slightly higher growth in Mn-and Fedeficient media than their non-transgenic counterparts, suggesting the transgenic protein may chelate these metals. S. cerevisiae carrying the altered poplar gene offers potential for bioremediation of Cd from wastewaters or other contaminated liquids.

Biosorption: A Review of the Latest Advances

“…In the same way, the expression of a non-MT cadmium-binding protein from Lentinula edodes significantly enhanced the cadmium biosorption capacity of transgenic Escherichia coli [35]. The transformation of the wild-type Saccharomyces cerevisiae with two versions of a Populus trichocarpa gene (PtMT2b) coding for a metallothionein allowed an increase in the intracellular content of cadmium in relation to the wild strain [36].…”

“…Some examples have recently been published in which different modification methods are used, such as esterification, graft polymerization, coating, treatments with acids, alkalis, methanol, cationic surfactants, formaldehyde or triethyl phosphate and nitromethane [30][31][32][33]. Although these modifications apply to dead biomass, living biomass can also be modified, but in a very different way, by genetic modification, which allows the introduction of genes into the desired biomass that increase resistance to the toxic effect of certain pollutants, or that increase the uptake of the pollutant (several examples with metals have recently been published) [34][35][36].…”

“…The deletion of the crpA gene (P-type ATPase) in the fungus Aspegillus nidulans showed 2.7 times higher cadmium biosorption capacity [92]. A transgenic yeast that expressed a metallothionein gene from Populus trichocarpa had higher intracellular Cd than the wild strain [36]. Through genetic engineering, a plant cadmium and zinc transporter (AtHMA4) was also used as a transgene to increase tolerance to these metals and the biosorption capacity of Chlamydomonas reinhardtii [93].…”

Novel Latex Microsphere Immunochromatographic Assay for Rapid Detection of Cadmium Ion in Asparagus

“…The current experiment of gene-knockout yeast strain intuitively explained why ITCBE had been used as a bifunctional chelator in the immunodetection of Cd 2+ [ 20 , 36 , 37 ]. In addition to our current research, other reports also indicate that yeast strains with special genotypes could be used to investigate Cd 2+ tolerance [ 38 , 39 ]. Additionally, we innovatively used yeast mutants to screen chelators against Cd 2+ , which has never been reported in previous studies.…”

Yeast Genomics and Its Applications in Biotechnological Processes: What Is Our Present and Near Future?

“…It can also withstand high salt and heavy metal concentrations and is being investigated for its potential as a heavy metal biosorbent [ 92 , 93 ]. Furthermore, S. cerevisiae has the potential to bioremediate toxic pollutants found in industrial effluent, such as arsenic, and it has been extensively researched as a biosorbent for a variety of heavy metals, including Pb, Cr, Zn, Cu, and Cd [ 94 ]. This microorganism-based method has numerous benefits including low operating costs, a smaller volume of sludge produced, and a high efficiency in detoxifying very dilute effluents [ 95 , 96 ].…”