The Flight of Migrating Microbes

Jul 30, 2010
Millions of microorganisms can travel on dust particles blown from areas like the Sahara Desert in Africa. Credit: NASA/SeaWiFS

Every day, millions of microorganisms reach Spain from the Sahara Desert and the Sahel region - by flying.

Louis Pasteur demonstrated back in 1861 that germs can move through the air, but it was only recently discovered that bacteria, funguses and viruses can travel thousands of kilometers stuck onto . show clouds that come close to the size of the .

For the first time, the international team on the Ecosensor project, funded by the BBVA Foundation, have analyzed these traveling using molecular biology techniques. As well as identifying the species, they have found that they colonize high-mountain lakes in the and the Pyrenees, and that the phenomenon is escalating with .

The "migration" of these microorganisms on African dust is most intense in spring and summer, and has been gathering momentum in recent years; at times multiplying their numbers ten times over. This is due, researchers say, to the drought afflicting the Sahel region for the last thirty years, itself a product of our changing climate.

An added spur is the loss of plant cover in Africa driven by changes in farming practices. It is reckoned that between 60 and 200 million tons of dust rise up from the Sahara every year; a material rich in nitrogen, phosphorous and iron with an important role in the growth of marine plankton, and even the fertilization of .

Ecosensor brings together an international team of atmospheric physicists and biologists led by Isabel Reche, of the University of Granada, and Emilio O. Casamayor, from the Blanes Center for Advanced Studies. The molecular biology techniques these researchers use allow them to detect almost all the organisms present in a given sample, in contrast to earlier methods which Reche explains revealed "a good deal less than there really is".

The Canary Islands bear the brunt

That is why until now we could not even identify 0.1 percent of the 500 bacteria present in a liter of air, and had no inkling of how they might affect their "destination" ecosystems. The Saharan dust spreads across the whole planet, but the prevailing winds - from the east - mean the regions most affected are the Canary Islands and the Caribbean (see satellite photos).

Ecosensor researchers have taken air samples in the places where it is easiest to detect the rain of microorganisms, such as high-mountain lakes. "Such spots have barely been altered by local human activity" Reche remarks, " so they are invaluable for studying the incidence of invading airborne microorganisms blown in from remote sources".

The lakes chosen are located in Sierra Nevada and the Pyrenees, as well as the Alps (Austria), Argentinean Patagonia, the Bylot Islands in the Arctic (Canada), and the South Shetland archipelago (Antarctica).

The researchers suck out air, filter it and extract the DNA of the organisms present. "By analyzing the genes we can tell what microorganism they belong to," Reche continues. They also separate the microorganisms to ascertain which can reach the lakes alive.

The Pyrenees mountains separate France and Spain. Dust from Africa has allowed microorganisms to migrate into lakes high in the mountain range. Credit: NASA

The same life in Sierra Nevada, the Pyrenees and Mauritania

Their results, which have recently appeared in various scientific publications, show that Sierra Nevada and Pyrenean lakes harbor microorganisms "that we have also found in the soil in Mauritania", says Reche. "It is truly amazing".

Among the microorganisms identified are Pseudomonas - a Bacillus genus capable of colonizing a wide range of niches; Staphylococci - a genus that includes microorganisms present in human skin, and Acinetobacter, which contribute to the mineralization of the soil. In general terms, they are considered to be non-pathogenic for humans.

But how might the advent of these new microorganisms affect local ecosystems?

"The increase in dust load in pristine ecosystems, like high-mountain lakes, has major repercussions" explains Reche, "because with it come nutrients that fertilize the lakes and alter their microbial communities".

Some of these changes have harmful effects; indeed the dust may already be damaging the fauna and flora of some ecosystems. Caribbean corals, for instance, are suffering decline due to excess dust deposition.

Another big question is, how do microorganisms manage to stay biologically active after their journey? The dust travels at between 2000 and 4000 meters altitude, exposed to severe dryness and harmful radiation; not all the organisms found form spores, so they must have other defense mechanisms at their command.

One hypothesis mentioned by Reche is "an increase in the quantity of protective pigments, which adhere to the mineral particles, conferring a degree of protection".

Explore further: Image: Underwater structures of the Great Bahamas Bank

Related Stories

Climate change effects on imperiled Sierra frog examined

Dec 11, 2008

Climate change can have significant impacts on high-elevation lakes and imperiled Sierra Nevada Yellow-legged frogs that depend upon them, according to U.S. Forest Service and University of California, Berkeley, scientists.

Cosmopolitan microbes -- hitchhikers on Darwin's dust

Dec 04, 2007

Scientists have analysed aerial dust samples collected by Charles Darwin and confirmed that microbes can travel across continents without the need for planes or trains - rather bacteria and fungi hitch-hike by attaching to ...

Recommended for you

Scientists make strides in tsunami warning since 2004

11 hours ago

The 2004 tsunami led to greater global cooperation and improved techniques for detecting waves that could reach faraway shores, even though scientists still cannot predict when an earthquake will strike.

Trade winds ventilate the tropical oceans

12 hours ago

Long-term observations indicate that the oxygen minimum zones in the tropical oceans have expanded in recent decades. The reason is still unknown. Now scientists at the GEOMAR Helmholtz Centre for Ocean Research ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.