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African Dust Microbiology in the Caribbean

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A satellite view of African dust blanketing the Caribbean
African dust: A satellite view of African dust blanketing the Caribbean on May 28, 1999. White arrow points to the U.S. Virgin Islands. [larger version - 69KB jpeg]
Summer storms and accompanying warm air can lift soil particles as high as 15,000 ft above the African deserts and then carry them across the Atlantic Ocean. Each year, several hundred million tons of African dust are transported westward by the trade winds to the Caribbean as well as to North and South America. About 50 percent of the African dust that reaches the United States affects Florida, while the rest may scatter as far northward as Maine and as far westward as Texas.

A long-term drought in the Sahel region of North Africa that began in the early 1970s, along with poor land-use practices and the drying of Lake Chad, is believed to have contributed to an increase in transatlantic dust over the past few decades. Coincident with the increase is a notable decline in the health of coral reefs in the Caribbean and Florida.

A hypothesis was put forth suggesting a relation between degradation of Caribbean marine species and airborne pathogens (bacteria, fungi, viruses) that could be transported with the African dust. The dust could also be contributing to human health problems, such as asthma.

Christina Kellogg checks windspeed and air temperature while taking a dust sample
Above: Christina Kellogg checks windspeed and air temperature while taking a dust sample on St. John, U.S. Virgin Islands. The liquid impinger, about the size of a lunchbox, is in the rocks to her left (circled).
Below: Dust samples are taken by using two different methods. The liquid impinger (small black box at left) bubbles air into a sterile liquid buffer in the glass tube. The vacuum pump (toolbox, foreground) sucks air through sterile filters in the bottom of the plastic cup unit on top of the PVC pipe.

dust sampling device, including liquid impinger and vacuum pump
To address these questions, our group (Eugene Shinn, Ginger Garrison, Dale Griffin, Christina Kellogg, and Chuck Holmes), in collaboration with the National Aeronautics and Space Administration (NASA), began a study to identify the microbes and pesticides transported with African dust, which could be affecting human and marine ecosystem health in both the Caribbean and the Eastern United States.

We have published results proving that African dust does carry living microbes. That work, involving culturing of air filters on agar, revealed the presence of bacteria and fungi, of which 25 percent are plant pathogens and 10 percent are opportunistic human pathogens.

The agar medium was chosen because cultivation and visible growth immediately answer the question, "Are these microbes viable?" However, the method limits detection to only those organisms that are capable of growing on that particular agar medium, which is typically only about 1 percent of the total population of bacteria and none of the viruses (which require a living host to reproduce).

The obvious next step is to develop methods that allow us to detect the total microbial community, which means being able to extract DNA (microbial genetic material) directly from the dust sample.

During July and early August, Christina hiked out to a remote sea cliff on the island of St. John (U.S. Virgin Islands) to test two new methods. She collected a series of air samples during periods of clear skies and periods of African dust events, using both a vacuum-pump/filter apparatus and a liquid impinger.

The new filters being tested can be dissolved in an organic solution to capture all the organisms on the filter. The liquid impinger works by bubbling the air sample through 25 milliliters of buffer, which catches even the smallest viruses that would pass through the filters. The DNA can then be extracted directly from the liquid buffer.

If these methods test well, we will be able to probe the microbial community DNA for specific pathogens of interest, such as the bacterium that causes white-plague disease in corals.

Related Sound Waves Stories
African-Dust Study Highlighted at Conference on Climate Change and Health Effects in the Caribbean
July 2002
Caribbean Coral-Reef Ecologist Studies Dust from the African Sahel
March 2002
Radio Interview Explores African Dust, Human Health, and Mystery Novels
March 2002
Lectures on African Dust
Dec. 2001 / Jan. 2002
Dust Collecting in the Caribbean
October 2001
USGS Briefs Department of Defense on African Dust Study
August 2001
African Dust Presentations
Dec. 2000 / Jan. 2001

Related Web Sites
Coral Mortality and African Dust Project
U.S. Geological Survey (USGS)
Conference on the Effects of Globally Transported African and Asian Dust on Coral Reef and Human Health
U.S. Geological Survey (USGS)

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in this issue: Fieldwork cover story:
Gulf of Mexico Gas Hydrate

Tampa Bay Coring

North Carolina Coastal Erosion

Endangered White Abalone

Marbled Murrelets

Research Sediment Core Drilling Proposal

African Dust Microbiology

Outreach Tall Ships

Gulf of Mexico Teacher Workshop

Coastal Louisiana Interview

MRIB Makes Headlines

Meetings U.S. Commission on Ocean Policy

Numerical-Modeling Workshop

Staff & Center News WHFC Employees Farewell

Sound Waves Staff

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