They came from above

They came from above All photos by Brendan Borrell Opportunistic infections seem to pop up out of nowhere, but new strains are appearing in new places, striking otherwise healthy animals - including humans. A few microbiologists go hunting. By Brendan Borrell n the spring of 2000, veterinarian Craig Stephen walked up to the biology department at Vancouver Island University in Nanaimo for what he thought would be a routine autopsy of a dead

By | December 1, 2008

They came from above

All photos by Brendan Borrell

Opportunistic infections seem to pop up out of nowhere, but new strains are appearing in new places, striking otherwise healthy animals - including humans. A few microbiologists go hunting.

By Brendan Borrell

n the spring of 2000, veterinarian Craig Stephen walked up to the biology department at Vancouver Island University in Nanaimo for what he thought would be a routine autopsy of a dead porpoise. "In my experience of doing stranded marine mammals, the vast majority of them, you don't get anything," says Stephen, who runs the university's Center for Coastal Health, "They've died, they've sunk, they've started to rot, they float back up, they get on the beach and then somebody finds them."

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Karen Bartlett holds up a petri dish dotted with Cryptococcus gattii colonies.

All photos by Brendan Borrell

Biologists now recognize that this dogma is only partly true, particularly in the face of Earth's warming climate. For example, over 50% of Kazakhstan's croplands have been sucked dry, while the Sahara expands into Nigeria and Ghana at a rate of 3,500 km2 per year. This global process of desertification is increasing the number of dust storms that ferry microbes across continents and oceans. Meanwhile, in the temperate zone, rising temperatures have rendered some regions more hospitable to colonization by microbial hitchhikers arriving on soils from tropical climes. This new fungal strain cropping up in people and other animals with healthy immune systems may have been a new arrival to Vancouver Island, or it may have always been tucked away in some hidden valley for many years, until one balmy summer triggered its unfortunate bloom. And there are hints that it is steadily furthering its progress. "The question we've been asking over the last 10 years," Hoang says, "Is it going to get to the mainland and will it spread across the Pacific Northwest?"

key moment in aeromicrobiology, or the study of airborne microbes, came in 1933, when Fred Meier of the US Department of Agriculture convinced Charles Lindberg to collect samples during an arctic flight from Maine to Denmark. Upon finding everything from fungal spores to algae and diatoms, Meier wrote, "the potentialities of world-wide distribution of spores of fungi and other organisms caught up and carried abroad by transcontinental winds may be of tremendous consequence." We now know that particles of dust, organic matter, and aerosolized water droplets support hardy communities of bacteria, fungi, and viruses—a mere 0.08% of which have ever been cultured.2

Some 10,000 bacteria are present in every gram of airborne sediment, and the atmosphere contains at least one billion metric tons of dust.3 That translates to a quintillion dust-borne bacteria—enough, according to Dale Griffin of the USDA office in St. Petersburg, Fla., "to form a microbial bridge between Earth and Jupiter." Over the course of five days in 2001, NASA tracked a large dust cloud that originated in the Gobi Desert as it moved east across the Pacific, North America, and the Atlantic, before petering out over Europe. Frequently, during African dust storms, a smoke-like strand is visible in satellite photos swirling off the continent, and looming over Italy, Spain, and southern France.

Emilo Casamayor and Maria Vila-Costa collect microbes from the surface of Lake Redo in Pyrenees.

All photos by Brendan Borrell

One of the most surprising new findings about airborne microbes is that far from being passive passengers of the wind, some are truly adapted to life in the mesosphere—70 km above the earth's surface—where they must constantly repair their DNA following bombardment by direct UV radiation. Or take a 2008 study that found that airborne microbes haunting Singapore shopping malls are not a random sample of what's outside, but are specialized for survival in the indoor air environment.2

ne morning this summer, microbial ecologist Emilio Casamayor from the Center for Advanced Studies in Blanes, Spain, and visiting postdoc Maria Vila-Costa hike past hordes of tourists and backpackers to Lake Redo, one of 1,200 alpine lakes in the Pyrenees Mountains. After finding a comfortable rock to squat on, the pair pull out metal mesh screens about one meter long and bound by a wooden frame. Vila-Costa presses her screen to the water's mirrored surface and lifts it into the air, a thin film bridging the wire grid. She tilts the screen to the neck of her plastic bottle and fills it one drip at a time. "How long does it take usually?" she asks Casamayor. "One liter, one hour," he responds.

The clock starts ticking, and Casamayor takes time to explain his work, which is aimed at understanding the effect of dustborne microbes on the native communities in the water. Most of the lake's biodiversity, he says, is restricted to this hydrophilic layer on the surface, where native microbes make use of nutrients coming from dust drifting in from Africa. He says that humic acids and other nutrients in atmospheric dust are easier for bacteria to break down than those from local soils, because they have been exposed to intense UV radiation. The dust particles also contain living microbes, and he wants to know how long they survive on the lake's cool surface. In addition to collecting and sequencing samples from 30 lakes in the region, Casamayor has set up a system to collect dust before it hits the lake and sequence organisms within it. These data will help him understand the impact of dust storms on microbial ecology.

Casamayor first noticed the dust in the Pyrenees back in June 2004, when his research focused on microbes living in the water. A late-season snowstorm had dumped fresh snow around Lake Redon near the town of Vielha and which sits at a slightly lower elevation than Redo. But when Casamayor came out to sample under the ice, he noticed the snow was already covered with a fine layer of brown grit. The phenomenon was not new—he had seen it in photos dating back to the 1860s—but with the drying of North Africa over the last 50 years, he reasoned that larger storms may be bringing more foreign microbes.

Indeed, the microbial community may be transforming in ways that scientists are only beginning to notice.

Around the same time the Cryptococcus outbreak began in Canada, scientists finally discovered what was killing sea fan coral in the Caribbean. Since the early 1980s, massive numbers of Gorgonia ventalina in the West Indies have been smothered by four highly virulent strains of Aspergillus sydowii,4 a common, cosmopolitan fungus that had never caused widespread disease in plants or animals. The virulent Aspergillus strains were later shown to have originated in Africa.5 The dust also brings crop pathogens such as sugar cane rust, Puccinia melanocephala, and banana leaf spot, Mycosphaerella musicola. During African dust storms, USDA microbiologist Dale Griffin says the number of culturable colonies of microorganisms airborne over the US Virgin Islands rises by a factor of 10. Since scientists began monitoring in 1973, an increase in African dust arriving on the island of Barbados has coincided with a 17-fold increase in asthma levels. In Spain, these dust clouds can have fatal consequences: A study published in the November issue of Epidemiology found that daily mortality in Barcelona increased by 8.4% during periods when African dust clouds were present over the region, possibly due to biological irritants and allergens.6

Casamayor began monitoring Pyrenean lakes last year, and one of the first organisms he found was Acinetobacter, an opportunistic pathogen that is highly resistant to antibiotics (see "7 But the presence of small numbers of the VGIIb subtype suggested that there had been a second introduction of the fungus. Both fungal strains were a single mating type, which later led Duke University researchers to suggest that the outbreak was the result of an unusual same-sex mating event (See sidebar "References

1. M.A. O'Malley. "The nineteenth century roots of 'everything is everywhere', Nat Rev Microbiol, 5:647-51, 2007.
2. S.G. Tringe et al., "The airborne metagenome in an indoor urban environment," PLOS One, 3:e1862, 2008.
3. D.W. Griffin, "Atmospheric movement of microorganisms in clouds of desert dust and implications for human health," Clin Microbiol Rev, 20:459-77, 2007.
4. K.B. Ritchie and G.W. Smith, "Cause of sea fan death in the West Indies," Nature, 394:137-8, 1998
5. J.R. Weir-Bush et al., "The relationship between gorgonian coral (Cnideria: Gorgonacea) diseases and African dust storms," Aerobiologia, 20:119-26, 2004.
6. L. Perez et al., "Coarse particles from Saharan dust and daily mortality," Epidemiology, 19:800-7, 2008.
7. S.E. Kidd et al., "A rare genotype of Cryptococcus gattii caused the cryptococcosis outbreak on Vancouver Island (British Columbia, Canada)," Proc Natl Acad Sci, 101:17258-63, 2004.

Comments

Avatar of: Darrell Coleman

Darrell Coleman

Posts: 1

December 3, 2008

As a scientist myself, I can only ask if they discovered the fungus and had the area destroyed. If not, why? It's like reading this article feels like like the Photographer in Natural Born Killers, but worse. We could be talking about major numbers here and I don't read that the area was burned our destroyed with anti-fungals. Fungals have killed most of the Oranges and Bananas already and most of the Colorful frogs of Panama. We could all wait and see, but why not get in there and stop it at the blue line, you darn Cannucks?
Avatar of: Greg Wooster

Greg Wooster

Posts: 2

December 4, 2008

Dear Editor,\n \nI enjoyed reading both "Baghdad Hack" and "They Came from Above". I thought I'd pass along some references to work I pioneered in, which involve the aerobiological dissemination of fish pathogens. Airbourne spread of disease may not be limited to only terrestrial animals.\n \nWooster, G. A. And P. R. Bowser. 1996. The Aerobiological Pathway of the Fish Pathogen Aeromonas salmonicida and it's Implications in Fish Health Management. Journal of the World Aquaculture Society. 27(1):7-14\n \nBishop, T.M., A. Smalls, G. A. Wooster and P. R. Bowser. 2003. Aerobiological (airborne) dissemination of the fish pathogen Ichthyopthirius multifiliis and the implications in fish health management. Pages 51-61. In Lee, C.-S., and O'Bryen, P.J., editors. Biosecurity in Aquaculture Production Systems: Exclusion of pathogens and other undesirables. The World Aquaculture Society, Baton Rouge, Louisiana, 70803. United States. 301 pages.\n \nAsley R.T., A. Barnes, D Stewart Fielder, R. Lester, and R. D. Adlard. 2006. Aerosol dispersal of the fish pathogen, Amyloodinium ocellatum. Aquaculture 257: 118-123.\n \n \n \n Sincerely, Greg Wooster
Avatar of: PHILIP TAYLOR

PHILIP TAYLOR

Posts: 1

January 5, 2009

Having recently identified a major source of yeast-like fungal emissions from Eucalyptus - Taylor et al (2006) Identification and possible disease mechanisms of an under-recognized fungus, Aureobasidium pullulans. Intl Arch Allergy Immunol 139:45-52 - may I suggest sampling directly from the flowers. Albeit, there can be some height issues to resolve. I suppose I shouldn't mention that in Australia it is common to shoot a branch from the tree for collection purposes.\n\nThe floral structures are rich in sugars (nectar), and possess mainly thin walled cells, This site appears ideal for high density fungal growth. This applies to many other plant species as well, and is especially prevalent where the climate has high relative humidity, and quiescent conditions prevail. \n\nI have noticed from past publications that sampling is routinely performed on leaves, bark and nearby soil, and even the air, whereas the inflorescence tends to be overlooked as a major fungal source.\n\nPhilip

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