Washington, Feb 1 (IANS): The clue to astronauts' immunity in outer space owing to prolonged travel lies in learning the negative impact of zero gravity on fruit flies.

A team of researchers from the University of California at Davis and the University of Central Florida (UCF) has studied the impact weightlessness has on fruit flies bred in space.

"Our study showed that a biochemical pathway needed to fight fungal infections is seriously compromised in the flies after space flight," said Laurence Von Kalm, a UCF biologist.

"More work would be needed to determine if similar effects occur in humans but this gives us some important clues," he added.

Fruit flies' innate immune system is similar to that of humans and other mammals and is often used as a model in basic studies.

The research team, led by UC Davis biologist Deborah Kimbrell, bred flies in space aboard Space Shuttle Discovery in 2006.

The flies developed into adults while on the 12-day mission.

The flies were retrieved after the mission and researchers found that they were more apt to get fungal infections.

Further analysis revealed that the system the flies use for detecting and defending against fungal infection was deactivated.

In contrast, another system used to defend against bacterial infection was not impaired in the space flies.

The team hopes to carry out research with fruit flies on the International Space Station (ISS).

"Getting a better understanding is particularly important, especially as we look to engage in long-term missions such as interplanetary space flights," added Kalm.

The findings were published in the journal PLOS One.