Walking in a Winter Wonderland, with Bacteria: Pseudomonas Syringae!
Updated: Aug 6, 2021
I have always loved the snow, until around the end of January, then it becomes less about holiday scenes and snow sports and more about shoveling the driveway and slipping on the ice wishing for warmer weather. Here in New England though, snow falls well past February, and winter storms have been known to break spring-longing hearts into April and even May in the mountains! But what on earth does falling snow have to do with microbes you ask? Like everything, our little friends are everywhere, and one of them, Pseudomonas Syringae, a bacteria, is a big part of natural and artificial snowmaking! You could call them the microbial snowflake architects!
Last year, I started winter hiking in the White Mountains of NH, crazy right? Why would anyone go out in the freezing cold, it's too dangerous! Well, it turns out to be absolutely amazing - there are no bugs (well, maybe a few), it's less people-y, and the snow covers all of the rocks and roots we usually have to step over! The bright white snow clinging to every surface against the deep greens of the evergreens and the blue sky paint incredible scenes everywhere you look, it's like walking through Narnia! I often stick out my tongue to taste the snow from the branches of the stubby trees along the trail, it's just water that froze up and fell from the sky, right?
As we've seen previously, microbes have both positive and negative impacts on our agricultural crops. A lot of research has been done to both eradicate and promote microbes on plants, one such study happened in 1978 in some wheat fields in Montana. They had been working to remove Pseudomonas syringae, which causes leaf blight and frost damage, from the plants, the soil, and even the irrigation water. Yet, the bacterium still found its way to infect the plants, but how?! David Sands, a professor of plant pathology at Montana State University had an idea that led him to hang out a plane window holding Petri dishes, and guess what he found?
P. syringae was floating around in the air and in the clouds and finding its way back onto the plants via rain and snow!
Sands knew that the bacterium caused frost on plants because it helps water molecules condense and form ice, even in temperatures above freezing.
What if it could do the same in the atmosphere he wondered? 20 years later, experiments found that bacteria can indeed serve as ice nucleators and survive to live another day! What's an ice nucleator you ask?
It might surprise you to know that snowflakes are not made up of just water! Most snowflakes are clusters of ice crystals that form around an ice nucleus, or ice nucleating particle (INP), in the atmosphere. Dust, soot, volcanic ash, organic matter, and fungal spores can all act as ice nucleators, but very commonly, it is Pseudomonas syringae that is carried into the air with moisture evaporation from the leaves of infected plants that become ice nucleators. When bacteria and other living microbes are part of the atmosphere it's called Bioprecipitation. Want to learn more about Bioprecipitation? Watch this: https://www.youtube.com/watch?v=mFJLFXhycSQ
It turns out that the key to P. Syringae's success in creating snowflakes (which it uses to hitch a ride to new areas to grow in) is a protein called InaZ. This outer membrane is extremely conducive to making this particular microbe into an excellent ice nucleator because of its structure and ability to mimic the surface of an ice crystal. This allows for the formation of snowflakes in lower clouds at warmer temperatures than in higher clouds. As water crystals form around the particle (ice nucleus), it gathers more crystals creating amazing formations and as it gets heavier, it falls through the atmosphere. The shape of the snowflake is determined by all kinds of factors as it travels earthward, which creates the uniqueness of each snowflake - kind of like people!
But we've also found ways to use this microbial function to create man (actually microbe) -made snow! P. Syringae's ability to create snow using its InaZ protein coating was commercialized in 1987, resulting in a product named Snowmax. Bacteria are grown in large-scale fermentation, then pelleted, freeze-dried, and finally irradiated. The product is then hydrated on-site and added to a water supply. According to the manufacturers, Snowmax International (Colorado, USA), snowmakers can achieve up to 40 % more snow by spraying the treated water high over the snow area. Whereas other high-temperature nucleators can only be used up to –6.5 °C, their product works at –0.6 °C and in lower humidity. There is, of course, controversy about this application, but the ski resorts love it!
So, the next time you stick your tongue out to catch one of those unique and wonderful snowflakes, remember, there could be a hidden surprise microbe held within (don't worry, Pseudomonas syringae is harmless to you), it's just trying to find a new plant to wreak havoc upon! The world covered in snow is glorious, I hope you get out there and enjoy the beauty of things seen and too small to see!