'Space bugs' grown in lab

It would be difficult to survive high up in the atmosphere

Samples of bacteria which some scientists believe may have come from space have been coaxed "back to life" by researchers.

It adds weight to a controversial theory which suggests that Earth could have been "seeded" by extraterrestrial micro-organisms.

The samples of bacteria and fungus were apparently collected from 41 kilometres above the planet's surface by a joint UK/Indian project.

The culture work in the laboratory reveals the organisms are forms common to Earth.

Possibility of contamination

Opponents of the extraterrestrial seeding theory were convinced that the bacteria collected were either only the result of cross-contamination during the experiment or had somehow travelled up from Earth's surface.

One of the bacteria samples grown in Sheffield

The latest research, led by Dr Milton Wainwright, from the University of Sheffield, tried to see if any of the organisms collected from 41 km up could be persuaded to divide and grow in culture.

He managed to culture and identify three species. Two were bacteria: Bacillus simplex and Staphylococcus pasteuri.

Both are found commonly in the environment, and neither is known to cause disease.

The third was a fungus called Engyodontium album. Again, this is a common and harmless mould.

'Freeze dried'

Dr Wainwright told BBC News Online that he was fairly certain that contamination was not an explanation.

He said: "None of those bacteria have ever been found in my lab, or the hospital as a whole, as far as I am aware.

"I think another explanation for how those bacteria got there has to be found."

Reviving the bacteria had been difficult, he said, as they did not tend to form colonies, as might normally be expected. "It was as if they had been freeze dried."

Hardy bacteria

The strains cultured by Dr Wainwright seemed to be resistant to the effects of UV - one quality required for survival in space.

Established wisdom suggests that bacteria in the air cannot get past the troposphere which extends up to approximately 17 km above the Earth - and that the effects of gravity would bring even micro-organisms back to the surface eventually.

Dr Wainwright said he could not rule out an unknown event pushing bacteria beyond this altitude, but said that proof that this had happened was lacking so far.

"Perhaps, if bacteria from Earth were able to get this far up, we can't rule out the possibility that we might be able to 'seed' other planets!"

The study results are to be published in the journal FEMS Microbiology Letters.