Monday, January 28, 2013

Clouds of bacteria found at airline-cruising altitudes: Study

Airplane passengers have a host of invisible company in that thin, frigid atmosphere outside their airplane windows.

High above the wispy, cumulous canyons below, commercial jetliners fly through clouds of bacterial microbes — including some forms of E. coli — at typical cruising altitudes, a U.S. study has revealed.

“I think that’s a good way to put it actually,” said Kostas Konstantinidis, an environmental microbiologist at the Georgia Institute of Technology and one of the paper’s co-authors.

“You have company up there.”

Indeed, the paper shows that microbes — some of which could be disease-spreading pathogens — exist in greater concentrations than the dust and sea salt particles that also populate the troposphere between 6.4 and 9.6 kilometers above sea level.

But these microbial fellow flyers are unlikely to pose a danger to airline passengers, Konstantinidis said.

First, he says, airliners are closed circuit crafts that don’t typically allow outside air in. And second — even at 10,000 cells per square metre — the microbes exist in concentrations too low to pose real disease dangers.

“But after this study I expect that some of them are pathogens,” Konstantinidis said of the high flying microbes.

“In my mind it’s very possible,” he said, adding new research will now attempt to better identify the bugs.

While posing no danger to passengers, the wafting microbes could explain how some pathogens may have crossed between continents in the days prior to rapid, long distance air travel, Konstantinidis says.

Lofted into the heavens by sea spray and hurricane winds, the organisms may form the nucleus of the ice particles that fall as rain and snow — bringing their micro-organic loads to Earth with them.

“This study is really interesting for microbial bio-geography, how microbes are transported between continents and so on,” Konstantinidis said.

The paper was published Monday by the journal Proceedings of the National Academy of Sciences.

And while airborne microbes have been found at the summits of the world’s tallest mountains, the paper marks the first time they’ve been located in the jet paths that millions of passenger flights ply every year.

To locate the organisms, Konstantinidis’ team flew a NASA DC-8 craft above two major tropical hurricanes – Earl and Carl – in 2010.

The plane was equipped with filtered sampling probes that trapped passing particles as the craft flew by.

These particles were then run through genomic scanners, which found more than 100 different brands of bacteria and other micro-organisms in each sampling.

This DNA testing, however, was not refined enough to specifically identify the bacteria — though at least one form of E. coli could be inferred from its genetic snippets.

With frigid temperatures, high ultraviolet blasts and minimal oxygen, the mid to upper troposphere seems an unlikely place for life to survive.

“It’s very harsh conditions from our perspective, but from their perspective it might be different,” Konstantinidis said.

“For example, the way we preserve microbes in the lab and keep them for years is by freezing them at minus 80 C.”

Some 60 percent of the microbes his team tested were alive when they were captured, he said.