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Stratocumulus Clouds contain microbial cells and bacteria over the Pacific Ocean

Image courtesy of Wikipedia article: “Stratocumulus Clouds”

How does a bacterial cell make it rain? To affect the weather, bacteria must first get into the clouds. But to get from the earth’s surface, on plants and animals and in soil, they must float upward in air. All bacteria love and need water. Why leave the moist comfort of the earth to go airborne? Bacteria, as well as viruses and disease-causing germs, travel through the air in microscopic droplets called aerosols. (When an aerosol contains something biological like a microbe, it is called a bioaerosol.)

Inside these almost weightless bioaerosols, bacteria drift into the atmosphere with wind and updrafts. Aeromicrobiologists (read my post “On Cloud Nine”) have discovered bacteria as far up as 25 miles. To survive up there bacteria find “Earth nutrients,” carbon-containing chemicals that are carried into the atmosphere and get trapped inside ice crystals, even hailstones. Some bacteria produce pigments in their outer wall to prevent being damaged by intensified exposure to ultraviolet rays at high altitudes. The bacteria Pseudomonas is famous (among microbiologists at least) for making a pinkish pigment, and this species can usually be found in any type of water from kitchen drains to clouds.

Clouds contain as many as 30,000 microbial cells per cubic foot. To cause rain, each cell clumps up with several others. Proteins on the cells’ surface attract water. The protein and water molecules than coalesce in the frigid surroundings in a rigid-looking pattern or lattice. Scientists call this process ice nucleation. The ice-water-laden lattice gets too heavy to stay suspended in the cloud and drops with millions of others. As they start to melt back into water … raindrops. For the science-inclined, call it bioprecipitation.

Aeromicrobiologists are now finding evidence that bacteria play a part in making lightning, too. Other hardy scientists gather bacteria from atop hurricanes to learn more about how they contribute to massive weather patterns. All these facts tell us that – like soil, oceans, and our digestive tract – the skies also have their own microbiome. Next time, I’ll introduce you to this new science: microbiomes.