Yeast experiments on Artemis I may help astronauts survive cosmic radiation in deep space
Ancient microorganism may hold one of the keys to helping humans tolerate cosmic radiation in space
When NASA's Artemis I lifts off from a launch pad in Florida, it will carry no human crew on a 42-day mission to orbit the moon and return to Earth. But experiments aboard the rocket could lead to solving a vexing problem that stands in the way of long-duration human space flight: cosmic radiation.
University of British Columbia pharmaceutical scientist Corey Nislow was just a toddler when Apollo 11 landed on the moon in 1969. The human crew spent less than a day on the lunar surface beyond the protection against cosmic radiation provided by Earth's magnetic field, which deflects it to the Van Allen belts around the planet.
Apollo 17, the last human voyage to the moon completed fifty years ago this December, lasted just 12 days.
"Once you leave the safety of the Van Allen belts," Nislow said, "there is no shielding currently available that can protect biological material, including crew members, from the effects of cosmic radiation."
Those effects can include everything from an increased chance of developing cataracts to cancer. The International Space Station (ISS) is in low Earth orbit (LEO) and astronauts aboard the ISS are inside the Earth's protective magnetosphere.
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But extended missions to the moon and what NASA expects could be a nearly two-year return trip to Mars pose serious risks.
"Frankly if we're going to Mars, a return trip will expose a crew member to between 10 and 100 times the allowable limit of radiation," Nislow said.
1st biological material beyond Earth's orbit in 50 years
The work Nislow and his collaborators are doing with NASA to mitigate the effects of cosmic radiation will send the first biological material beyond Earth's orbit in 50 years. And the stand-in for flesh and blood astronauts is something most people have in their pantry: yeast.
"Even though yeast and human beings are separated by a million years of evolutionary time, half of all yeast genes function nearly identically to human genes," Nislow said.
Yeast, a single-celled microorganism, has about 6,000 genes. Nislow, who holds the Tier 1 Canada Research Chair in translational genomics, says the yeast cells in the experiment aboard the Orion spacecraft atop Artemis I have been individually altered to produce 6,000 genetically unique versions. Each version has a different gene removed and replaced with a short splice of unique DNA known as a barcode, which allows researchers to readily identify and track the variant.
Once the spacecraft is beyond the protection of the Earth's magnetic field, the dried yeast will be remotely rehydrated so it can grow and divide while bombarded with cosmic radiation. Five or six weeks later, when the spacecraft splashes down in the Pacific Ocean, the shoebox-sized container holding the experiment will be recovered and returned to Nislow's lab at UBC. The hope is to find individual genes in the cells that withstood the radiation or were able to repair any damage.
"And then we can ask what drugs or chemicals at our disposal might help lessen the sensitivity of a particular gene and that's where we get toward looking at countermeasures," Nislow said.
Yeast cells make the perfect astronauts
It's a fascinating opportunity, according to Prof. Doug Boreham, a radiation biologist at the Northern Ontario School of Medicine in Sudbury.
"They're going to be looking at the survival when they get these things back, which is very cool," Boreham said, noting that yeast cells make the perfect astronauts. "They don't need to breathe. They don't need water. They don't eat. They don't care what temperature it is. But yet they're alive."
In fact, yeast cells are such ideal surrogates for human ones that they are at the core of a different experiment aboard Artemis that Boreham and his colleagues are helping to support. BioSentinel is a small satellite the size of a cinder block that will be deployed in deep space. It contains yeast samples that will be rehydrated in stages over a period of weeks using a blue nutrient solution.
The solution turns pink as the yeast metabolizes and an optical sensor on board will measure the colour changes. Cells that can't repair the damage from cosmic radiation will be less pink and more blue. But the samples won't return to Earth for study. BioSentinel will transmit the data as it orbits the Sun until it runs out of power.
Boreham is involved in the project science, which he says will involve comparing data from BioSentinel with that from samples grown simultaneously at his university and two kilometres underground at SNOLAB, Canada's deep underground research facility.
"We're looking at the fundamental mechanisms that are involved in cells managing and repairing the effects of cosmic radiation," Boreham said, acknowledging that there are limitations to the experiments.
Single-cell organisms like yeast just want to grow and divide, he says. Human cells, however, can "communicate" with each other. Human cells exposed to stress and damage like radiation create free radicals, which stimulate our immune system. Humans also have tumour suppressor genes, which can cause the self-destruction of cells that are beyond repair.
"You can't get that in a yeast model," Boreham said.
'Very important experiments'
But it's all critical work, according to Canadian astronaut Dr. Roberta Bondar.
"Those are very, very important experiments and those are things we need to do very soon," Bondar said.
Bondar, who is a neurologist, flew aboard NASA's space shuttle Discovery 30 years ago and went on to analyze astronaut health data from two-dozen missions. She says the effects of radiation on any long-duration space flight could wreak havoc on the mission.
"So that includes things like altered cognitive functions or maybe even impaired motor functions and behavioural changes," Bondar says. "These are things that would be scary in a closed environment in some type of spacecraft."
Nislow believes that until a way to mitigate those radiation risks has been found, it would be unethical to send humans on any space voyage lasting more than a year.
And he's hoping that experiments using one of the oldest life forms on the planet make it possible for humans to safely travel to other worlds.
"Without being hyperbolic, it's a very very important step."
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