A teaspoon of yeast is among the cargo on the Russian vehicle Progress that blasted off on Thursday for the International Space Station. The yeast is part of an experiment that will study the effect of microgravity on gene expression, with the long-term goal of learning how to safeguard human health in space.
The study was funded in 2002 but seems particularly timely now, coming shortly after US President George W Bush outlined an initiative that will focus ISS firmly on advancing human spaceflight.
“Yeast is a model microbial organism,” says Cheryl Nickerson, a microbiologist at the Tulane University Health Sciences Center in Louisiana, US, and one the study’s leaders. “Its cell structure is closely related to human cell structure, so we can use it to predict how humans might respond to spaceflight.”
Yeast has about 6400 genes and the researchers have sent many different strains into space, each missing a different gene. The yeast, currently in a dormant phase, will be mixed with a growth factor once aboard the ISS.
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It will then be allowed to grow for 72 hours, before one of the ISS’s crew members will turn a crank in the apparatus to stop the growth and preserve the yeast in a “freeze frame”. The experiment will most probably be brought back to Earth for analysis in April.
Turned on
Back on the ground, the researchers will isolate DNA from the yeast cells and put it on a microarray chip. This will identify which genes were “turned on” during the yeast’s time in orbit. Comparison with control strains grown on the ground will reveal the effect of microgravity.
A 72-hour experiment may appear to have little relevance for human spaceflight – especially on year-long missions to Mars, for example – but yeast replicates itself about every two hours. And the researchers have been granted several months of experimental time on a future ISS mission.
Previous research, including a study by co-investigator Tim Hammond of Tulane University and the VA Medical Center in New Orleans, Louisiana, shows microgravity may have significant effects on gene expression.
Human kidney cells grown on the space shuttle for six days in 1998 showed changes in the activity of 1600 out of 10,000 genes. By comparison, only half as many changed in a ground-based microgravity simulator and just five genes changed in a ground-based lab dish.
Super bugs
How microgravity affects gene expression is not known, but Hammond has speculated in the past that it might be because weightlessness resembles the environment of an embryo in the womb.
Gravity may “play a fundamental role in regulating gene expression in all cells and might also have had a fundamental role in evolution,” says microgravity researcher Stephen Moorman of the Robert Wood Johnson Medical School in New Jersey.
He says gravity could act indirectly, affecting the concentration of metabolites around cells, or directly, giving cells small signals of force that direct their development. “Flying yeast provides the opportunity to collect data that might allow us to test these types of ideas,” he told New Scientist.
Nickerson believes her teams’ work is also important as it could shed light on whether any bugs that hitch a ride on spacecraft could become nastier due to altered gene expression.
Research using ground-based microgravity simulators has already shown that some pathogens, such as salmonella, can become more resistant to antibiotics, she says, and spaceflight is known to weaken astronauts’ immune systems. “You can’t quarantine an infection in flight,” Nickerson says.
