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High above the Amazon jungle, a dusty traveler is about to complete a nearly 5,000-kilometer journey. This traveler—a speck of dust—was picked up by the wind in the heart of the Sahara Desert and swept across the Atlantic Ocean, one mote of the 182 million tonnes of tiny particles that make the journey each year. Wherever it lands, this nutrient-rich dust will nourish life, forging a vital link between disparate ecosystems. At their best, these plumes are the seeds of life, but as new research shows, they can also sow disease.
If the dust settles on the ocean, rather than on land, the phosphorus and iron it bears will trigger a bloom of microorganisms, including disease-causing Vibrio bacteria.
Different types of Vibrio bacteria can cause ailments ranging from seafood poisoning to cholera. Though Vibrio usually make up only a small part of the surface ocean microbial community, University of Georgia microbiologist Erin Lipp has shown that the arrival of Saharan dust can cause Vibrio populations to boom. These booms are a threat to public health that, until recently, scientists have struggled to explain.
“There’s been a lot of research to try to understand the effects of dust reaching ocean waters,” says Lipp. But she notes that this is one of the first studies to look at how specific microbe populations respond to the influx of nutrients brought by the dust.
In the lab, Lipp and her colleagues found that introducing Saharan dust into samples of Florida surface water caused Vibrio populations to spike. Tracking how Vibrio responded in the wild in Florida to dust plumes during the summers of 2013 and 2014 showed a similar relationship.
The response was striking: bacteria populations skyrocketed, largely within the first 24 hours. Wild Vibrio populations increased 30-fold and went from roughly one percent to nearly twenty percent of the total microbial community. “They’re able to respond very, very quickly to fluxes of nutrients and trace metals,” says Lipp. “We think one of the reasons they’re so well adapted to becoming pathogens is that they have this ability to be good opportunists.”
Saharan dust feeds the rainforest, but it also feeds a health risk. “The Vibrio have the potential for invasion, infection, and disease,” says Rita Colwell, a microbiologist at the University of Maryland. Colwell suggests that the public health risk will likely increase as climate change influences other environmental factors known to contribute to Vibrio growth, such as warmer water temperatures and increasing salinity. “Vibrio respond very quickly to temperature upshifts,” Colwell cautions. “If it goes from 15 °C to 17 °C, that’s enough for the bacteria to become very aggressive.”
Identifying how and when organisms respond to dust plumes is fundamental to understanding how dust drives ecosystems, says Lipp. Saharan dust links desert to rainforest and continent to continent, feeding phytoplankton and dangerous pathogen alike.