It’s well known that the human gut is a thriving bacterial ecosystem—not to mention the skin, lungs, and various other parts of the body. But the breadth and depth of microbes’ participation in many systems on the planet are still not widely understood. For instance, there is evidence that there are microbes in the clouds, hitching thousand-mile rides through the atmosphere and helping to cause rain or snow along the way.
Some of these cloud microbes seem to come from the soil, but others are likely rising up out of the ocean, a riotous soup of bacteria and viruses. In a new study in Nature Communications, researchers used a 13,000-liter tank of seawater to observe what microbial species are in the water and which manage to become airborne in sea spray, thus launching themselves into the atmosphere.
The work was intended to help answer a long-standing question: Exactly how do microbes rising out of the ocean connect to the planet’s climate? Substances released from the ocean may help manage global temperature, according to Kim Prather, an atmospheric chemist at the University of California, San Diego, who has pioneered the study of microbes in the sky. “If you put out different types of spray, you could make clouds that are brighter and whiter to cool things down,” she says. “Depending on what comes out of the ocean, it could really change the temperature of the planet.”
For the experiment, Prather’s team drew thousands of gallons of water from the Pacific into a long, enclosed tank in a lab, where the atmosphere had been carefully filtered so that the only microbes in it would come from the water. The researchers encouraged the organisms to grow, provoked wind and waves, and sampled furiously from the resulting spray. They performed a quick genetic test to identify what was in there, and found that indeed, not everything that lived in the ocean was making it out.
In particular, certain groups of bacteria were much more likely to rise into spray than others. Corynebacterium, of a type often found on the skin of people living around Prather’s university in San Diego, she says, was found to be more prominent in the spray than it was in the water, for instance. When the researchers dug into why, they found that these particular bacteria have cell-wall components that repel water. “These guys have waxy walls,” Prather says. “Of course they’re going to get out.” Viruses that were encased in fat-containing membranes managed to leave easily as well.
Now that the researchers have scratched the surface of what gets up into sea spray, the issue becomes whether these same microbes are the ones that have been found in clouds. Prather says that the organisms up there have not yet been fully identified, but gathering more samples with balloons or specialized planes is a plausible next step. The group also plans to repeat the sea-spray experiments using seawater from different times of year, or seawater inoculated with cultures of sea-going microbes from elsewhere in the world, to see how the results change.
Another route will be to pump in different amounts of carbon dioxide into the tube’s air to study the effects of the rising levels in Earth’s atmosphere. “One of the questions is, what happens to the microbes—what happens to all these processes—when you get to a more enriched CO2 atmosphere? What happens when we hit 600 parts per million, which we will?” says Prather. “We want to do those experiments now, so we can predict where we’re going.”