you're reading...


Genetically Modified Yeast Can Clean Up Wastewater

Reviewing: Sun, G.L., Reynolds, E.E. & Belcher, A.M. Using yeast to sustainably remediate and extract heavy metals from waste waters. Nat Sustain (2020).

DOI: https://doi.org/10.1038/s41893-020-0478-9


Toxic heavy metals in wastewater should be cleaned up

The outbreak of Minamata disease, a neurological disease caused by mercury poisoning, has alerted the public to be aware of the risks of mercury exposure. People in Minamata City, Japan, had been eating shellfish and fish with high levels of methylmercury absorbed from industrial wastewater for over 30 years, until the epidemic broke out in 1956. This still leads to intense debates over whether eating too much fish would expose people to too much mercury. Many people still wonder if eating a can of tuna every day is safe, or if pregnant women should be limiting or avoiding fish consumption.


Mercury is a type of heavy metal, along with other metals like copper, lead, cadmium, and zinc. They are called “heavy metals” because they are literally heavier than the “light” metals – a dime-sized disk of mercury would feel heavier on your palm than an identical piece of aluminum. Heavy metals naturally exist in Earth’s crust, and they enter the ocean as the rivers wash away the rocks and soils, or as wind blows dust particles into the ocean.

However, humans have been introducing additional heavy metals to the environment by burning oil and coal, producing cement, steel, electrical switches/lightings and batteries, and discharging industrial wastewater and sewage sludge into rivers. When these heavy metals get into the ocean, most of them accumulate in the sediments at the bottom of the ocean, but some are absorbed into marine plankton and move up the food chain, eventually accumulating in larger fish like tuna and mackerel that we consume. Exposure to high levels of mercury can cause a variety of symptoms such as nausea, respiratory problems, kidney disorders, tremors, paralysis and brain damage.

Tuna is the most common source of mercury in our diet. Large fish like tuna and swordfish feed on smaller fish that contains mercury, so they tend to have higher mercury than smaller fish.

To reduce the health risks associated with heavy metal, we need to clean up heavy metals from our waste and from our oceans. One strategy that has been recently getting research attention is bioremediation: using natural living organisms like microbes and bacteria to treat contaminated waters.

Scientists have discovered microbes that produce hydrogen sulfide (H2S), a chemical compound that smells like rotten eggs. Hydrogen sulfide reacts with heavy metals dissolved in water to produce metal sulfides, which are solid and will separate from water (a process called “precipitation”). However, these organisms grow very slowly under specific living conditions that cannot be easily maintained, so they haven’t been thought of as a realistic solution to cleaning up wastewater. To find a solution to this problem, Sun et al. (2020) worked on genetically modifying yeast to make it produce hydrogen sulfide and remove heavy metals from wastewater.


How can yeast remove heavy metals from wastewater?

Yeast is the same ingredient you put into that loaf of bread in your oven, or into a beer fermenter in your basement. It is a fungus that is very common in the environment, and has been used by humans since the ancient Egyptians discovered its ability to raise bread. Nowadays, yeast manufacturing is a billion-dollar business, and there are many different types of yeast supplied to different industries, such as baking, beer and wine, bioethanol and pharmaceuticals.

Yeast produces amino acids, which are the building blocks of proteins essential for its growth. Some of these amino acids contain sulfur, and to produce these sulfur-containing amino acids, yeast first takes up sulfate (a form of salt with sulfur), converts it to hydrogen sulfide, then finally converts it to the amino acids. Scientists have identified a number of genes in yeast that control each step of these sulfur-conversion processes. Each of these genes were deleted to produce “knockouts”, so that these knockouts lose the ability to convert sulfate to amino acids. By testing each knockout for its efficiency of metal removal, specific genes that play the most important roles in converting hydrogen sulfide to sulfur-containing amino acids could be identified.

Sun et al. (2020) confirmed that the yeast knockouts can produce hydrogen sulfide, and that the hydrogen sulfide produced by yeast can successfully remove metals from water, by growing the knockouts in waters that had roughly a hundred times higher copper, lead, cadmium and mercury than drinkable water. Copper and lead were most quickly removed, followed by cadmium and mercury, but four rounds of precipitation removed >99% of all these metals, to an amount low enough to drink safely.

(Figure 2c from original paper: each figure shows precipitates of metals (copper, zinc, cadmium, lead and mercury) by a yeast knockout strain. New yeast knockout cultures were supplied at each round. The diminishing color over multiple rounds of treatments shows incremental removal of heavy metals.)

The research team also attempted to control the shape and structure of the heavy metals that are precipitated on the yeast surface. This was because the traditional heavy metal removal techniques by adding chemicals such as lime and sodium hydroxide produce precipitates with heavy metals and chemicals all mingled together – like different colors of Play-Doh all mashed up – and as they cannot be separated from each other easily, they all need to be dumped into landfills or burned. While the research team successfully managed to regulate the size and shape of metal precipitates on the yeast surface to some degree, additional work needs to be done to determine how to remove these metal particles from yeast and recycle them efficiently.


Why is the genetically engineered yeast promising for the future?

We are generating large quantities of industrial, agricultural and electronic wastes that contain toxic heavy metals. This waste, untreated or only partially treated, gets discharged into the environment, polluting rivers and oceans. When heavy metals get stored in living tissues and organs of marine organisms, they do not degrade over time, and eventually get transferred to larger predators. Large amounts of heavy metals can be detrimental to the growth, survival and reproduction of marine organisms, and consuming these heavy metal-contaminated organisms is a potential threat to public health.

Currently, industries use chemicals to treat wastewater, but these chemicals produce harmful sludge that needs to be buried or composted in landfills. The chemicals also need to be renewed each time after wastewater gets treated, so treatment costs build up quickly. But yeast may be a cheap, widely available alternative to the chemical treatments. More than one million tons of yeast were produced in 2015, and a global production and supply chain of yeast already exists. Genetically engineered yeast is very easy to grow, as it can survive a wide range of temperature, acidity and oxygen concentrations.

Yet additional work is necessary to successfully implement the yeast-bioremediation in the near future. As mentioned above, a cost- and time-efficient way to remove the metals precipitated on the yeast surface still needs to be developed, so that both heavy metals and yeast can be recycled. In addition, as some heavy metals like mercury and cadmium are particularly more threatening to human health than others like calcium and zinc, selectively or preferentially precipitating specific heavy metals can be much more practical.

Nevertheless, a wider application of genetically engineered yeast may significantly reduce the cost of wastewater treatment and sludge disposal, keep heavy metals out of our oceans and reduce environmental threats and health impacts from toxic waste to both humans and the marine ecosystem.


No comments yet.

Post a Comment


  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 9 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com