Microbes hitchhike across Atlantic on desert dust

ORLANDO May 24, 2006 -- Bacteria and fungi, some with the potential to cause disease in plants or animals, may be finding their way from Africa to the Americas by hitchhiking on microscopic dust particles kicked up by storms in the Sahara, according to research presented today at the 106th General Meeting of the American Society for Microbiology in Orlando, Florida.

"This study presents evidence of early summer survival and transport of microorganisms from North Africa to a mid-Atlantic research site," says Dale Griffin of the U.S. Geological Survey in St. Petersburg, Florida, one of the researchers on the study.

Griffin and his colleagues tested air samples on a research ship in the middle of the Atlantic Ocean during May and June 2003 to determine if airborne, viable populations of bacteria and fungi could be detected and also to see if total population counts increased with the presence of airborne desert dust.

"The phenomenon known as desert-dust storms moves an estimated 2.2 billion metric tons of soil and dried sediment through the Earth's atmosphere each year. The largest of these events is capable of dispersing large quantities of dust across oceans and continents. Since a gram of desert soil may contain as many as 1 billion bacterial cells, the presence of airborne dust should correspond with increased concentrations of airborne microorganisms," says Griffin

Viable bacterial and fungal populations were collected on 24 of 40 sampling days. The three days where the highest populations were collected corresponded with the two highest periods of dust activity as determined by the U.S. Navy's Naval Aerosol Analysis and Prediction System Global Aerosol Model.

DNA analysis matched two of the isolates 100 percent to two dust-borne isolates previously collected from the atmosphere in Mali. One of them, a known human pathogen, has also been found in atmospheric samples in the U.S. Virgin Islands when African desert dust was present. Additional analysis identified a number of bacteria and fungi capable of causing disease in animals and plants, including the cause of Florida Sycamore canker.

"It is tempting to speculate that transatlantic transport of dust could be a vector to renew reservoirs of some plant and animal pathogens in North America and could also be the cause of new diseases," says Griffin.

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