As if astronauts on the space station didn’t have it tough enough. Not only do they have to contend with radiation, space junk and a dampened immune system, bacteria that are normally harmless on Earth turn nasty in microgravity.
Now researchers in the US think they know what’s behind this microbial maliciousness – they're hungry.
Luis Zea, an aerospace engineer from the University of Colorado, and colleagues compared Escherichia coli bacteria which had a stint on the space station with those on Earth – in particular, which genes were switched on and off.
In the journal PLOS One, they found E. coli in space dialled up genes linked to starvation mode. These genes boost a bacterium's virulence in an effort to find food.
They probably kick into gear, the researchers write, because bacteria are less able to transfer molecules – including glucose, their main energy source – between each other while floating in space.
The work could help protect astronauts from infections during long-haul missions.
Microbiologists have studied bacteria in space since satellites carrying microbes were launched in 1960.
Since then, they’ve discovered that some bacteria in reduced gravity multiply faster and become more virulent and less susceptible to antibiotics. But little evidence was found to explain why they take on these new traits.
So Zea and colleagues prepared E. coli cultures. Half were sent to the space station on 9 January 2014 and allowed to grow in various antibiotic concentrations for nearly 50 hours before being frozen and returned to Earth in May and October 2015.
The space bacteria ended with much higher cell counts and were able to grow in stronger antibiotics than their Earth-bound counterparts.
And when the researchers measured their gene expression, all signs pointed to reduced extracellular transport – or fewer molecules being passed between cells.
“When we started seeing the gene expression data, the story that the cells were telling was very obvious, almost like numbers popping out of the computer screen,” Zea says.
Future research will examine a variety of other bacteria in zero gravity. But knowing why some harmless bacteria bring out their bad side in space is a huge step towards keeping future astronauts healthy.