My Cousin Yeast
A famous chemical spill in West Virginia led a scientist to wonder what exactly had spilled into the river. So she watched the reaction of yeast, a very distant relation to humans.
Jennifer Gallagher was at the Morgantown Municipal Airport to pick up her dad when she found the industrial chemical on the Internet that she wanted to order.
The chemical was 4-methylcyclohexane methanol, also known as MCHM. It was a coal-washing chemical that most people, including Gallagher — a geneticist at West Virginia University — hadn’t heard of until about 10,000 gallons of it spilled into the Elk River in January 2014. Charleston’s water supply was shut down and eventually 300,000 residents were urged not to use the water in any way if they could smell the telltale licorice odor that followed even trace amounts of the chemical.
When she contacted the company, they wanted to give her a tankard. She wanted five grams. They settled on a paint can full of MCHM. The next step was to bring the chemical to work and introduce it to her collection of yeast.
“I was like, look, I just want to know what it does,” Gallagher said. “I mean, I have the tools. I have the interest. I had developed this model for assessing cellular effects of different chemicals.”
What she found shows how much we still don’t know about the chemicals we produce every day, how our bodies work and how chemicals and biology interact.
Yeast is a good candidate for chemical testing. It doesn’t seem like the tiny, white and pasty microorganisms are anything like us. But if you count billion year-old common ancestors, yeast is a very distant cousin. We both mate and produce children and are made of the same basic building blocks from the same planet.
There’s one particular similarity that is the reason Gallagher has a lab full of circles of yeast on Petri dishes: The way we process chemicals. Humans developed to have seven biochemical pathways. Yeast only has one. That makes it simpler to understand, and while it takes decades for human families to generate and grow, Gallagher’s lab has one yeast pair that has created 1,000 offspring. Her graduate student Apoorva Ravishankar has created two yeast genomes that are either completely or mostly sequenced after becoming resistant to the pesticide Roundup.
Gallagher has also exposed yeast to 4-Nitroquinoline 1-oxide, a poison used to induce tumors in rats for research. She took yeast — which reproduces in an hour and a half — and introduced it to chemicals it had never met, seeing how it withered or adapted with resistance.
The standard for U.S. chemical testing is to see how much of a substance it will take to kill a rat. Gallagher says death is one clear outcome from testing. But that result doesn’t show us how a chemical affects life immediately in other ways and in the long term.
When she exposed yeast to MCHM — in a study that has been funded by the National Institutes of Health — the yeast stopped growing. But when her grad student Michael Ayers removed the chemical, they started growing again like nothing happened.
Then it was time for her colleagues to move up the life ladder and test the chemical on African clawed frog tadpoles. At low doses, the tadpoles froze. Tapping their Petri dishes got no reaction. Like the yeast, when Gallagher and her students took the MCHM away, the tadpoles went back to life as normal. When they exposed the tadpoles to a higher dose — much higher than the concentration in the Elk River — they showed developmental defects, including a curved spine and skin cells that didn’t move properly.
Gallagher has some ideas about why this is happening. It could be that the chemical inhibits the creatures’ muscles. Or it could be that their nervous systems are affected.
The next step in the research is to move on to zebrafish, a species that is similarly affected by MCHM. Assistant professor Sadie Bergeron will give them MDMA. If they move under the power of the stimulant, their muscles aren’t inhibited, and it’s their nervous system that is putting on the brakes. The idea hasn’t been tested yet but Gallagher believes it’s probably their nervous systems that are being halted.
So how much does it matter that some tadpoles and zebrafish are paralyzed by this chemical?
Gallagher points out that as we develop resistances to chemicals in our microbiome, our biology is changing and will be passed down to our descendants.
“You put them in the environment,” she said of chemicals, “they are going to affect organisms and they are going to change in response to them.”
“And what I’m interested in is how do they respond to it and how do they change over time? And are there multiple ways to become resistant? Is it just one way and they’re following that same path or do you have different paths to the same end?”
When she saw the MCHM spill in the news, she saw people complaining of lung irritation, she saw people who couldn’t use their water and she saw a chemical interaction she didn’t understand.
The episode was a reminder that it’s the moments between the start and end of life that make us who we are. When we come into contact with chemicals, do we resist? And as we resist, how are we changed forever?