Bacteria Assists in Formation of Ice and Snow Chances are, that pile of snow in your yard contains bacteria — but not because it's dirty. New work in the journal Science suggests that bacteria may have played an important role in forming those snow crystals. Researchers explain the connection between microbiology and meteorology.
NPR logo

Bacteria Assists in Formation of Ice and Snow

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript
Bacteria Assists in Formation of Ice and Snow

Bacteria Assists in Formation of Ice and Snow

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript

JOE PALCA, host:

For the rest of this hour: bacteria and snow. A new discovery may make you think twice about eating snow. This week, researchers report in the journal Science that plant bacteria has been found in snow samples from around the world. But the bacteria is not just hanging out in the flaky, white stuff, scientists think the microorganism actually helps form snow up in clouds. If confirmed, their discovery is one of the first to link biology with climate.

But how does a plant bacteria make snow or get into the clouds? Well, here to explain the research and answer some of those questions is Brent Christner, an assistant professor and glacial microbe researcher at Louisiana State University.

Welcome to the show, Dr. Christner.

Dr. BRENT CHRISTNER (Assistant Professor, Biological Sciences, Louisiana State University): Good afternoon, Joe.

PALCA: And I should just point out that if you want to learn more about our topic we have links at and you are also welcome to ask questions of Dr. Christner at 800-989-8255. That's 800-989-TALK.

And I guess my first question is what's somebody at Louisiana State University doing, talking about snow in the first place?

Dr. CHRISTNER: Exactly, right, not a lot of snow in Louisiana. It just so happens I do a lot of research in areas of the world where there is no fall.

PALCA: Oh dear, we seem to have lost the call, but we'll have Dr. Christner back on the line in just a second. We are doing a little bit of adjustment to the line, so…

Are you there, Dr. Christner? Can you hear me?

Dr. CHRISTNER: Yup, I am here.

PALCA: Oh, good, okay that seems much better. You are saying, you do a lot research in parts of the world that are a little cooler than Louisiana.

Dr. CHRISTNER: That's right. We do research in Antarctica, and I just moved here recently and I have been in Montana for about four years, so access to a lot of snowy environments.

PALCA: I see, well, maybe we need a little bit of you know, basic biology or basic physical chemistry if it is, I guess, to start with of why snow is, to begin with, or why raindrops fall?

Dr. CHRISTNER: Yeah. So all snow and most rain fall initiates in the atmosphere due to ice formation in clouds. So it's well recognized that ice nucleators, which are substrates that water molecules bind to are important to this process. The nature of these nucleators is not well known. Our study contributes to this and that we've been able to show that biological particles which are able to catalyze ice formations at temperatures warmer than would normally occur are widely distributed in the atmosphere.

PALCA: Really? Now, let me see if I got this straight. So in other words, there is this moisture in the atmosphere and something has to happen to make the moisture turn into a droplet or make it turn into a snowflake and sometimes that - I gather, it's sometimes it is a particle of dust but sometimes you are saying it is actually a bacterium?

Dr. CHRISTNER: Yeah, it is a particle of dust can make ice at temperatures which are relatively cold. But the difference with these biological particles and specifically bacteria, they are capable of catalyzing ice formations at temperatures much warmer than those that a simple dust particle would.

PALCA: And how could that be? I mean, how would a biological organism work at a different temperature from a piece of dust?

Dr. CHRISTNER: Well, these very interesting bacteria have a protein which is on the exterior of the cell, and they bind water molecules in a fashion that mimics the ice crystal lattice.

PALCA: Ah, I see.

Dr. CHRISTNER: So they are much more efficient at catalyzing ice formations than simply a mineral dust particle.

PALCA: So how did you find these bacterium or bacterial bits associated with snow? Where did you find them?

Dr. CHRISTNER: Well, initially, we started to look in local snows that were in Montana. And with colleagues and in connection with some other field work that I have done, we were able to collect snowfall samples from worldwide locations. We assumed that if plants are the biggest sources of these particles, that we would find them in locations and during times of the year when plants are most productive.

And actually the results that we have are consistent with this. For example, when we go to a place like Montana and France, these are areas where there is vegetation and in fairly close proximity. We find the highest concentration of these particles in the precipitation that we've analyzed. And we expect it, we go to a place like Antarctica, a place that does not have terrestrial vegetation, we would find them perhaps not at all. And what we found is there are much lower concentrations in places like the polar regions. But the concentrations are not zero, we can still detect them. And this indicates that these particles, if they're originating from plants, are widely distributed in the atmosphere. When they are traveling through the atmosphere, they are able to retain this ability to catalyze ice nucleations.

PALCA: Wow. And so, I suppose, I mean, I guess maybe I am jumping ahead of you, but do you - is there a way to determine where the particular plant bacteria came from off of the earth and I presume carried up into the atmosphere by evaporation or rising air currents or something? Can you tell where it is coming from and how it is distributed? And maybe how it is affecting global temperature? Boy, I am getting a big question here.

Dr. CHRISTNER: Yeah, it is a big question. It is difficult for us to actually determine the sources of these particles, but it is possible that we could learn, look at the other factors in the precipitation that could give us clues, as to where the particles originated. We assume that if we go to a place like Louisiana, and we find these particles that they may be originating from local vegetations, but it is actually difficult for us to constrain those sources.

PALCA: Okay, let's see if we have a call now and go first to Robert(ph) in Concord, California.

Robert, welcome to SCIENCE FRIDAY.

ROBERT (Caller): Hello. We know that minor changes in the environment of the ocean have a huge impact on microorganisms, and I was wondering if there might be some huge implications with minor changes in the global atmospheric environment that might have huge impacts on these microorganisms and maybe even change snowfall and rainfall patterns.

PALCA: Interesting question, Robert.

What about that, Brent Christner?

Dr. CHRISTNER: Yeah, that's a good question. Well, I will give one example on how potentially a rise in global temperature may affect the distribution of these particles. One of the bacterium in which this process has been studied in the most detail, is an organism called Pseudomonas syringae. This is an organism that is present on plant leaves and is a pathogen in a number of agriculturally relevant crops. If this organism is important in the precipitation cycle - and one key thing is that the organism doesn't like to grow in really warm temperatures, so it's possible that a rise in temperature in a particular geographical region will actually inhibit the growth of these bacteria, and possibly affect climate.

PALCA: Hmm. Sounds - again, every time you think you understand something in the climate debate, something gets a little more complicated.

We're talking about the role of bacteria, or bits of bacteria, parts of bacteria in forming ice crystals and snowflakes and raindrops in the clouds.

I am Joe Palca, and this is TALK OF THE NATION from NPR News.

And let us take another call now and go to Mike(ph) in Rapid City, South Dakota.

Mike, welcome to the program.

MIKE (Caller): Hi, thanks. We are suffering through a horrible drought here in the west, and I'd like to know if this technology or this new science can be used in cloud seeding or could it help improve cloud-seeding technology at all?

PALCA: Cloud seeding…

MIKE: I'll take my answer off the air.

PALCA: Okay. Thanks.

What about that Brent Christner?

Dr. CHRISTNER: Well, it is possible that you could use a nucleator like this to induce precipitation. I mean, for over sixty years, weather modification has occurred by distributing particles like dry ice and silver iodide into clouds. And you know, you certainly could think about using this organism to do a similar thing, although people may not be too excited about spraying a microorganism out of an aircraft. But alternatively, if you could actually plant vegetation, that encouraged this organism to enumerate, by controlling what crops are planted, you may actually be able to influence climate.

PALCA: Wow. Interesting. Now, were you the first person to discover this relationship between bacteria and snow formation or snowflake formation?

Dr. CHRISTNER: Well, these bacteria have been known about for a long time and I should be clear in saying that we have not established a direct link between these organisms and climate as of yet.

PALCA: Ah, okay.

Dr. CHRISTNER: But what we have shown is that they are widely distributed in the atmosphere. And atmospheric sizes are actually very surprised that they're as abundant as we found.

PALCA: All right. Let's try one more call and go to Grant(ph) in Marietta, Ohio.

Grant, welcome to the program.

GRANT (Caller): Hello.

PALCA: Hello.

GRANT: Yeah, I was just - I have always heard you don't eat the yellow snow…

(Soundbite of laughter)

PALCA: It's, you know, that's what I was thinking when I said it earlier.

GRANT: Yeah, well, I was just wondering if, you know, you could get sick from eating this snow with the bacteria in it.

PALCA: Ah, interesting.

GRANT: That's pretty much the extent of my question.

PALCA: Okay. Interesting question.

What about that, Brent?

Dr. CHRISTNER: You know, I am really glad you brought that up because in your intro, you sort of suggested that we maybe need to rethink about what's falling out of the sky and how damaging this could be. And that is not an angle that I support at all.


Dr. CHRISTNER: If fact, you're going to consume more bacteria by drinking a glass of tap water, than you would by opening up your mouth and getting a snow flake…

PALCA: Maybe you can explain what you mean by that because I know what you are giving is the analogy but now you are going scare people into thinking they shouldn't drink tap water.

Dr. CHRISTNER: No, I don't want to do that either.

(Soundbite of laughter)

Dr. CHRISTNER: What I just want to say is that bacteria are ubiquitous.

PALCA: That was the point really.

Dr. CHRISTNER: Yes, they are everywhere.

PALCA: We were joking, I mean, I suppose I shouldn't take liberties but we were just suggesting that it might make somebody feel funny if they knew they were eating or drinking a lot of bacteria when they drink their tap water but they are, and so maybe they should know that.


PALCA: But anyway…

Dr. CHRISTNER: But I still suggest steering clear of the yellow snow.

PALCA: Now, the yellow snow, well, at least there is something we can definitely all agree on. Well, that is all the time that we have at this afternoon for this discussion but very interesting.

Where do you go next to look for bacteria in your snow?

Dr. CHRISTNER: Well, there is really a large portion of these particles which we can identify as biological and we need to do more work to actually find out what kinds of organisms they're coming from. And now that we know that they're abundant in precipitation, we need to take it to the next step, and we need to connect the presence of these particles with climate. And to really do this, we need to be able get in the clouds and collect this material directly rather than setting out a bucket and collecting what's falling out of the sky.

PALCA: All right, well, good luck for that. And when we see your next paper in Science, we'll come back to you.

Dr. CHRISTNER: Thank you, Joe.

PALCA: Okay. Thanks, Brent Christner.

Brent Christner is an assistant professor and glacial microbe researcher at Louisiana State University.

Greg Smith composed our theme music and we had help today from NPR librarian, Kee Malesky.

If you have comments or questions, write to us at SCIENCE FRIDAY, 4 West, 43rd Street, Room 306, New York, New York, 10036. The e-mail address is Check out for more information and links to today's program. You can listen to past editions of SCIENCE FRIDAY online or take them with you as a pod cast. And check out SCIENCE FRIDAY's Kids' Connection, free curriculum materials for teaching science using Just click on the teacher's link on Ira Flatow will be back next week.

For NPR News in Washington, I'm Joe Palca.

Copyright © 2008 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.