Using yeast to sustainably remediate and extract heavy metals from waste waters

Our demand for electronic goods and fossil fuels has challenged our ecosystem with contaminating amounts of heavy metals, causing numerous water sources to become polluted. To counter heavy-metal waste, industry has relied on a family of physicochemical processes, with chemical precipitation being one of the most commonly used. However, the disadvantages of chemical precipitation are vast, including the generation of secondary waste, technical handling of chemicals and need for complex infrastructures. To circumvent these limitations, biological processes to naturally manage waste have been sought. Here, we show that yeast can act as a biological alternative to traditional chemical precipitation by controlling naturally occurring production of hydrogen sulfide (H2S). Sulfide production was harnessed by controlling the sulfate assimilation pathway, where strategic knockouts and culture conditions generated H2S from 0 to over 1,000 ppm (similar to 30 mM). These sulfide-producing yeasts were able to remove mercury, lead and copper from real-world samples taken from the Athabasca oil sands. More so, yeast surface display of biomineralization peptides helped control for size distribution and crystallinity of precipitated metal sulfide nanoparticles. Altogether, this yeast-based platform not only removes heavy metals but also offers a platform for metal re-extraction through precipitation of metal sulfide nanoparticles.