BACTERIA may be able to make it rain without ever leaving the ground – if the powerful detergents they produce can reach the clouds, that is.
Previous studies have suggested that bacteria can affect cloud formation. For example, an analysis of snow samples has hinted that bacteria swept up into the atmosphere trigger precipitation so that they can return to the ground.
Now Barbara Nozière of Stockholm University, Sweden, and colleagues suggest that surfactants secreted by many species of bacteria could also influence the weather. While these are normally used to transport nutrients through membranes, the team have shown that they also break down the surface tension of water better than any other substance in nature. This led them to suspect that if the detergent was found in clouds it would stimulate the formation of water droplets.
To find out if they were present in the atmosphere, Nozière collected air samples over a coastal region, an ocean, a forest and a jungle at locations in Brazil, Sweden and Finland. Particles in all the samples contained minute amounts of detergent with a chemical structure that resembled the surfactants. It also broke down the water into droplets in the same way. “The only thing we know of that could cause this strong an effect is the bacterial surfactants,” Nozière said in a presentation at last month’s meeting of the American Geophysical Union in San Francisco.
Nozière suggests that the bacteria may be helping to keep the atmosphere healthy and active. She also speculates that they evolved the ability to summon water from the sky to help them survive.
The next step will be to work out how these substances get up to the clouds, says Andi Andreae of the Max Planck Institute of Chemistry in Mainz, Germany. Only a small proportion of cloud-forming particles come from the ground, carried by the wind. “This bacterial gunk could hitch a ride on particles that travel from the surface to the clouds and supercharge them,” he says.