The fog that settles over a field at night looks empty. For hours, in the dark, inside droplets too small to see, something may be waking up, dividing, and multiplying. When the fog lifts, it may release more life back into the air than was there before.
A new study tracked 32 fog events over two years at a research site in central Pennsylvania and found something that changes how we should think about the air we breathe. In six events where researchers compared air before and after fog, the post-fog air contained roughly 45 percent more bacteria on average. The fog hadn't just passed through; it may have been giving them a place to grow.
Published in mBio, the research points to fog droplets functioning as a temporary, active microbial habitat, one where bacteria get pulled in from the surrounding air, switch on, eat, grow, and divide, before being released back into the sky in greater numbers when the water evaporates.
Read More: Newly Discovered Microbes Cleanse Water That Trickles Through Soil
Fog Bacteria Turn Droplets Into a Temporary Home
The bacteria found in fog water are physically different from the same bacteria drifting as dry particles in the open air. They are larger, roughly five times the volume of their dry-air counterparts. They are also dividing more frequently. At any given moment during a fog event, about 2.4 percent of bacterial cells in the water show visible signs of active division, compared to about 1 percent in dry air particles.
Explore All OptionsBoth are consistent with active growth. Bacteria that are metabolizing and multiplying get bigger before they split. The fog, rather than simply ferrying microbes from one place to another, may actually be giving them somewhere to live.
The dominant resident was a pink-pigmented bacterium called Methylobacterium. Across the sampled fog events, the group made up nearly a third of bacterial reads in fog water. Methylobacterium specializes in eating a family of simple carbon compounds, the same family that includes formaldehyde.
Fog Microbes May Help Break Down Formaldehyde
Formaldehyde is present throughout the atmosphere, produced by vehicle emissions, industrial processes, and the breakdown of other organic compounds. It is toxic, and the bacteria living in fog are breaking it down at roughly 200 times the rate previously measured in cloud water.
On a per-cell basis, the bacteria in fog water are breaking down formaldehyde at rates close to the maximum ever observed in lab cultures, meaning they are working near their biological limits. Most of that activity appears to serve detoxification more than growth — the bacteria may be breaking down the toxic compound because it would otherwise harm them. In the process, they may be quietly removing a common toxic compound from the air.
Why Fog Harvesting May Need More Caution
The discovery also complicates the idea of fog as a clean, simple source of water. In parts of the world where freshwater is scarce, fog harvesting, collecting water from fog using mesh nets, has been promoted as a clean and sustainable drinking water source. The bacterial concentrations found in this study suggest that fog water is anything but sterile.
Bacterial densities in fog droplets were comparable to those found in productive lake or ocean waters. For communities that collect fog water to drink, often under the assumption that it is clean and safe, that may be worth knowing. Some Methylobacterium species can also act as opportunistic pathogens under certain conditions, which adds another reason to treat harvested fog water with caution.
The atmosphere, this research proposes, should be rethought not as an empty vessel that passively carries microbes from one location to another, but as a living habitat where bacteria may not just survive the journey but also use it to grow.
Read More: Hidden Bacteria in Marine Snow May Be Dissolving Ocean Shells — and Disrupting Carbon Storage
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in mBio: Growth and formaldehyde degradation of photoheterotrophic Methylobacterium within radiation fogs
