Drying Out Microbe-Filled Droplets

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Images of ocean spray and sneezing, showing how microbes can get aerosolized in particles. Text reads, "Microbes often survive in aerosolized droplets of complex compositions, containing salts, polymers, and other solutes."

Images of three drying droplets: 1) water with bacteria; 2) water with salt; and 3) water with bacteria and salt. Text reads, "However, droplets containing both salt and bacteria exhibit striking drying dynamics."

Three images of a drying droplet viewed through different modalities. Text reads, "The DNA stain reveals that bacteria deposition and salt crystallization are correlated."

Ocean sprays, coughs, and sneezes are just a few of the ways that droplets full of bacteria and salt can get aloft on a breeze. How do these bacteria stay viable even as their droplet evaporates? That’s the question behind this video’s research.

When a bacteria-laden droplet or a salt-laden droplet dries, the evaporating droplet’s contact area shrinks, leaving behind only a concentrated lump of bacteria or salt. But when droplets contain both salt and bacteria, the drying droplet’s contact line gets pinned, leaving a larger area stain. The bacteria’s presence seems to promote crystallization of the salt, which–in turn–traps water in isolated spaces, perhaps helping the bacteria stay viable longer. (Video and image credit: R. Ran et al.)

Animation of three droplets drying out. When all three components–water, salt, and bacteria–are in a droplet, the drying process looks very different.