Plumes across the Pacific deliver thousands of microbial species to North American West Coast

Dec. 17, 2012 — A surprising number of microorganisms -- 99 percent more kinds than had been reported in findings published just four months ago -- are leaping the biggest gap on the planet. Hitching rides in the upper troposphere, they're making their way from Asia across the Pacific Ocean and landing in North America.

For the first time researchers have been able to gather enough biomass in the form of DNA to apply molecular methods to samples from two large dust plumes originating in Asia in the spring of 2011. The scientists detected more than 2,100 unique species compared to only 18 found in the very same plumes using traditional methods of culturing, results they published in July.

"The long-range transport and surprising level of species richness in the upper atmosphere overturns traditional paradigms in aerobiology," says David J. Smith, who recently earned his doctorate at the University of Washington in biology and astrobiology. He's lead author of a paper in the current issue of the journal Applied and Environmental Microbiology.

"It's a small world. Global wind circulation can move Earth's smallest types of life to just about anywhere," Smith said.

It's been estimated that about 7.1 million tons (64 teragrams) of aerosols -- dust, pollutants and other atmospheric particles, including microorganisms -- cross the Pacific each year. The aerosols are carried by wind storms into the upper reaches of the troposphere. The troposphere, the layer of air closest to earth up to about 11 miles (18 kilometers), is where almost all our weather occurs.

Co-author Daniel Jaffe, professor at UW Bothell, has previously documented especially large plumes of aerosols in the troposphere making the trans-Pacific trip in seven to 10 days. The recent findings are based on two such plumes, one in April and the other in May of 2011, detected at Mount Bachelor in the Cascade Mountains of central Oregon.

Most of the microorganisms -- about half were bacterial and the other half fungal -- originated from soils and were either dead on arrival or harmless to humans. A few fungal species have been associated previously with crop wilt but scientists had no way of determining if any crops were affected during either plume event.

Most of the species in the plumes can be found in low, background levels on the West Coast. The plumes, however, brought elevated levels of such organisms leading the scientists to say that it may be useful to think about microorganisms as air pollution: microorganisms that are unnoticed in background levels might be more relevant in concentrated doses.

"I was very surprised at the concentrations. One might expect the concentrations of cells to decrease with altitude based on fallout and dilution," Smith said. "But during these plume events, the atmosphere was pooling these cells just as it does with other kinds of air pollution."

Interestingly, Smith says, two of the three most common families of bacteria in the plumes are known for their ability to form spores in ways that they can hibernate safely during harsh conditions, making them especially well adapted to high altitude transport.

"I think we're getting close to calling the atmosphere an ecosystem," Smith said. "Until recently, most people would refer to it as a conveyor belt, or a transient place where life moves through. But the discovery of so many cells potentially able to adapt to traveling long distances at high altitudes challenges the old classification."

Cells also can interact with their high-altitude environment, for example, becoming the nucleus for rain drops and snow flakes and influencing the amount of precipitation that falls. Other scientists estimate that 30 percent of global precipitation stems from microbes.

On the other hand, scientists have yet to see evidence of metabolism or growth of microorganisms while aloft and there's a limited amount of time that any organism might reside there.

Sampling the upper troposphere for microorganisms in the past has been a spotty effort using aircraft and balloons, Smith said

"Because it is so difficult to get samples, I argue it's probably the last biological environment on the planet to be explored," he said.

Mount Bachelor, like many other mountains in the Cascades, has a peak tall enough to pierce the upper troposphere. Unlike other mountains in the Cascades, however, the top of Mount Bachelor is a far more accessible place for an observatory because a ski area exists there. There's power and bringing equipment and personnel to the observatory is not a major undertaking, you just take the ski lift.

Funding for the work came from the National Science Foundation, National Geographic Society, NASA's Astrobiology Institute, the UW's NASA Space Grant Consortium and the UW Department of Biology.

Other co-authors are Peter Ward and Hilkka Timonen with the UW and UW Bothell respectively, Dale Griffin with the U.S. Geological Survey, Michele Birmele and Michael Roberts with NASA and Kevin Perry with the University of Utah.

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The above story is reprinted from materials provided by University of Washington. The original article was written by Sandra Hines.

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Journal Reference:

D. J. Smith, H. J. Timonen, D. A. Jaffe, D. W. Griffin, M. N. Birmele, K. D. Perry, P. D. Ward, M. S. Roberts. Intercontinental Dispersal of Bacteria and Archaea in Transpacific Winds. Applied and Environmental Microbiology, 2012; DOI: 10.1128/AEM.03029-12

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Biologist treks across Southwestern China to answer the 'killer mushroom' question

Dec. 6, 2012 — McMaster University biologist Jianping Xu trekked over 30 kilometers a day through mountainous terrain and inclement weather in southwestern China to discover that a wild mushroom wasn't at the root of 400 unexplained deaths.

His findings, published online in Applied and Environmental Biology, shattered a myth started by a 2010 article in the journal Science, claiming the Trogia venenata mushroom contained high concentrations of the metal barium, causing high blood pressure, cardiac arrests and sudden deaths in southwestern China over the past 30 years. The deaths mainly occurred in small villages, some of which saw nearly one-third of their population perish quickly.

"Although there was no published evidence supporting the theory that barium in the T. venenata mushroom was the leading culprit of what was called Sudden Unexplained Death (SUD), it was picked up as a fact by almost all of the major news media," said Xu, associate professor of biology and a member of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University. "These reports caused significant concern among the public about potentially high levels of barium in wild edible mushrooms in southwest China."

Every summer since 2009, Xu and his team have travelled across the Yunnan province, collecting fruiting bodies of T. venenata as well as other mushrooms from villages severely impacted by these deaths.

Researchers tested the mushrooms and found the barium concentration was so low it would require a person weighing 150 pounds to consume at least 35 kg of dried T. venenata for it to be lethal. In fact, the barium concentration in these mushrooms is the same as in common foods, such as fresh meat and poultry.

The majority of SUDs, since 1978 in Yunnan Province, occurred in apparently healthy people, mostly young females, during the rainy season from June to August.

While previous studies suggested certain mushrooms could accumulate heavy metals, there was no information about high levels of barium in wild edible mushrooms. The speculation and subsequent media reports generated significant concern among health officials, the general public and all levels of government and severely impacted the economy by affecting trade of many wild, edible Chinese mushrooms, such as Matsutake, truffles, morels and Chanterelles.

Although Xu's results show these mushrooms contain low levels of barium, he says barium can't be ruled out as a contributor to the deaths, given that high levels of barium were found in the blood, urine and hair samples of some of the victims. Yet, his study does suggest that barium in mushrooms was unlikely the leading cause. "Though there are a couple of leads," he said, "further investigation is needed to discover what the true cause was for these mysterious deaths."

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