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.
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.
in this issue:
African Dust Microbiology