Photo credit: NASA

This week marked a burst of springtime weather in my region, including several prolonged episodes of rain. Of course, the warming temperatures, increased hours of sunlight, and occasional rain help wake up the plants and start a new season of renewal and growth. But it’s been less obvious to scientists what impact rain has on microorganisms.

One science headline this week on this topic caught my eye and got me thinking again about this topic: engineers from MIT have demonstrated how light rain creates aerosols from raindrops. The upshot of their study is that when rain hits the soil, miniature air bubbles trap bacteria and bounce up, then burst and send the bacteria flying through the air. So, these airborne droplets are inadvertantly instrumental in both capturing and dispersing bacteria. This could help the bacteria colonize new locations–and possibly serve as an underappreciated mechanism for the spread of certain human diseases. This study has been summarized in some detail in a ScienceDaily release and with photos and video from the mechanical engineers at MIT who did the study in an article in Popular Science. (For all the nitty-gritty scientific details, you can check out the original scientific report in Nature Communications). This story may sound a bit esoteric, but it illustrates how little we know about soil microbes and their equally tiny habitats. It also demonstrates how researchers can team up across disciplines to investigate unanswered questions using novel approaches!

This study reminded me of another connection between rainfall and microorganisms that I read a couple of years ago, this time about fungi. Many fungi are multicellular and create large numbers of spores that disperse into the air and help the fungus reproduce. In some species, the condensation of water around the spores helps create weight that pulls the spores downward. As the water falls to the ground, the spores then shoot upward into the air. In an interesting twist, the sheer number of these spores (billions of them) drift around the world in the atmosphere and continue to attract water around them, which may create new raindrops that fall to the ground somewhere far from the original parent organism. That fungi may not only benefit from rain but actually help create it is a fascinating (and mind-boggling) idea to ponder a bit. See the image below for a little about fungal life cycles, and for more on this story, see this article in Popular Science.

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(This image has been created during “DensityDesign Integrated Course Final Synthesis Studio” at Polytechnic University of Milan, organized by DensityDesign Research Lab in 2015. Image is released under CC-BY-SA licence. Attribution goes to “Anita Righetto, DensityDesign Research Lab”. (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)%5D, via Wikimedia Commons)

Meanwhile, don’t overlook all those bacteria sprayed up from the soil by aerosols or other methods of dispersal. In 2016, it was reported that some common soil bacteria are endowed with proteins that are very good at attracting ice crystals when the bacteria are present in clouds. The change in the states of matter of water (solid vs. liquid) high in the atmosphere, aided by the partnership with bacterial cells, may make liquid water fall more readily in the form of rain.

So, bacteria AND fungi both may be contributing to the water cycle that keeps them (and us macroscopic life forms) alive. Some scientists are even pondering whether we could engineer clouds by “seeding” them with microbes to create precipitation over drought-stricken regions, a growing concern with changes in precipitation patterns predicted by climate change models.

I’m sure there will be more to these stories in the years to come. In the meantime, don’t forget your umbrella…spring is on its way!