Winter is coming. Microbe edition.

My fellow bloggers at FTDM have started a series of posts dedicated to the clever ways trees and salad greens survive freezing conditions. I’d like to continue the topic with how bacteria survive freezing.

For some bacteria, they actually create ice crystals on purpose.

If you can't beat the ice, join it?

The bacteria of interest is Pseudomonas syringae, a well-documented plant pathogen that can promote the freezing of water at warm temperatures via a process called Ice Nucleation (IN).

This ability is mediated by a protein -- the IN protein -- that the bacterium attaches to its outer membrane. This protein is unique in that it mimics the lattice structure of ice. This ice-like shape encourages water molecules to play along, causing ice to form around the bacteria at warmer conditions.

But, why would the bacteria want to form ice? Forming ice around your cells is much better than within your cells. If you have ever heard or seen the consequences of severe frostbite, you can appreciate why you do not want ice to form inside your cells; your cells can rupture and cause very painful, irreversible damage.

Many bacteria, including Pseudomonads, survived the ice age well before plants even existed on our planet. As a result, scientists speculate that this IN ability of bacteria might have evolved as a way to avoid this kind of cell damage when glaciers were common.

Bacteria may have evolved this ability millions of years ago but what consequence do ice-forming bacteria have on us today?

First off, Pseudomonas syringae, in addition to being a plant pathogen, can harm plants without causing disease by forming ice on the surface of plants and causing frost damage. 

Potentially damaging frost on lingonberry leaves that could have been caused by  Pseudomonas syringae .

Potentially damaging frost on lingonberry leaves that could have been caused by Pseudomonas syringae.

Second, this bacterium is not limited to forming ice on plants.

Bacteria might also be responsible for weather.

Associating with water is not limited to water on the ground; this Pseudomonas bacterium can actually be found flying around in the atmosphere. In fact, bacteria actually use the sky as some sort of microbial freeway.

Dating back as far as the 1980s, scientists have noticed microbes were present in the air. The first documented cases of aerial bacteria revolve around a troublesome plant disease that seemed to spread no matter what the farmers did. Flying an airplane above the infected field holding a petri dish out the window revealed that the responsible microbe was, in fact, in the air.

Microbiological methods have also gotten better since holding petri dishes out of airplane windows; genetic work sampling microbial DNA has revealed surprisingly large concentrations of bacteria at high altitudes in the atmosphere.

Some of the bacteria floating around in the sky are also able to form ice via IN. The end result? Bacteria floating around in the atmosphere can actually encourage weather events like rain and snow.

Bacteria present in the atmosphere recruit water molecules with this IN protein and ice forms. This ice then falls to the earth either melting along the way producing rain or remains frozen producing snow. Sampling ice crystals may actually reveal bacteria at the center.

Since lightning is actually caused by the collision of charged ice particles, bacteria might also be largely responsible for lightning!


Controlling weather through microbes.

Now that we know bacteria help dictate weather patterns, the obvious follow-up question is whether or not we can put this information to use.

Researchers (at Louisiana State University, for example) suggest P. syringae, capable of IN and already associated with plants, could be sprayed on crops in drought-prone areas to promote rain. In theory, the bacteria would enter the atmosphere and cause rain that otherwise wouldn’t have necessarily occurred.

We have a long way to go, but the possibility is certainly intriguing.

So, next time it snows, thank your microbes and remember to stay hungry! 


Like this? Check out other ways microbes influence our lives: 

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Does Size Matter? Evolution Says Yes

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