Microbes have an incredible ability to thrive in different environments. Extensive research has shown the vital roles that these invisible organisms play in the ecosystems of marine and soil environments.
But the atmosphere is another important habitat. Growing evidence shows that microbes in the Earth's atmosphere can affect rainfall, land fertilization and food production. Little is known, however, about how these tiny life forms adapt to living in air and the even broader role that airborne microbes may play in the planet's ecosystem.
The W.M. Keck Foundation awarded Emory University physicists Justin Burton and Minsu Kim $1.2 million to explore these mysteries. In a collaboration with the University of Oregon, the researchers will use the funds to pioneer new methods for mechanistic studies of the physiology, metabolism, ecology and evolution of airborne microbes.
The Emory project will create new tools to conduct never-before-done studies of how microbes adapt to living in air.
"We've developed a prototype acoustic levitation system that opens the door for air-culturing microbes in a well-controlled laboratory environment for the first time," says Burton, associate professor of physics.
The Burton lab specializes in studying the fluid dynamics of natural phenomena, from the molecular to the geographical scale.
The Kim lab specializes in using advanced biophysical techniques to characterize microbes from the molecular to cellular level.
"We are helping to take the field of air biology into a new era," says Kim, associate professor of physics. "Most research into microbe ecology has focused on microbes from marine and soil environments. We're expanding the possibilities for investigating atmospheric microbes."
The Emory researchers will collaborate with additional principal investigators on the Keck Award project: Earth scientist Joshua Méndez Harper, a former postdoctoral fellow in the Burton lab now at the University of Oregon, and Josef Dufek, professor of Earth sciences at the University of Oregon.
Wind-blown dust circulates globally, emitted by volcanic eruptions, wildfires and dust storms. These airborne particles can carry minerals and other nutrients across long distances. Desert dust from the Sahara, for example, is an important source of phosphorous for the Amazon rain forest.
It is also well-known that microbes — including viruses, fungi and bacteria — hitchhike on atmospheric dust. Perhaps the most striking example of how atmospheric microbes can impact the environment is the so-called rain-making bacterium Pseudomonas syringae that has been isolated from clouds. Research shows that this bacterium may play a role in the precipitation cycle by producing an enzyme that catalyzes ice formation.
Key impediments to further studying such atmospheric phenomena are sampling and culturing microbes in the air.
The Keck-funded project will develop an airborne-culturing method using acoustic levitators, each about the size of a microwave oven, that simulate atmospheric conditions. The levitators will work by creating standing waves of sound, just like a musical instrument, but at a frequency well outside of the range of human hearing. These high-intensity sound waves create high pressure that is capable of suspending particles in air that are as dense as copper.
Initially, the project will focus on studying bacteria, believed to make up more than 50% of atmospheric microbes. The controlled, laboratory conditions of the levitators will allow the researchers to home in on how different species of bacteria adapt to living in the harsh conditions found in the atmosphere, such as extreme temperature shifts, high humidity and solar radiation.
The bacterial species studied will include some that the researchers collect from the atmosphere through balloon experiments. Team members at the University of Oregon will release a series of small, ultralight balloons. They will float on easterly winds across the country at altitudes between five and six kilometers, which is comparable to those of Saharan dust clouds and wildfire plumes. Each balloon will house sterile titanium booms affixed with tiny sponges to trap microbes within their pores.
Balloon positions and sensor data — including temperature, pressure, humidity and dust concentration — will be transmitted continuously using amateur radio bands. As the balloons fly over Georgia, descent will be controlled using parachutes. GPS beacons will be enabled upon landing, allowing the researchers to pinpoint and recover the balloons.
The methods developed in the lab, and the resulting data, will be open source. Scientists around the world can build on the work and continue to push the boundaries in the field of air biology.
"The award from the Keck Foundation is giving us the freedom to strike out in bold new scientific directions," Burton says.
