Bacteria make rain : Bioprecipitation part I

As a kid in rural Alberta, Canada, Russell Schnell was mesmerized by storms, fascinated with how out of the dark clouds came hailstones, chunks of hardened water that shot through the cold wet air, pummelling the earth like bullets.

In 1968, as an undergrad, he helped the Alberta Research Council study hail, in a project that ranged over 10,000 square miles of Alberta farmland. His task - figure out how the process by which water vapor in clouds could turn into hail, a phenomena not well understood back then.

Pondering the matter, Schnell recalled as a kid that he had noticed hail formed most often near forests, or where there was a lot of vegetation. He conjectured that trees were releasing some organic matter into the air that was causing the water vapor to nucleate into ice. When Schnell told his hypothesis to his atmospheric science professors, though, they chuckled at him, dismissing his ideas as that of a novice who didn’t know better.

Why were the professors so dismissive? Lets unpack this a bit. It had do with something called normal science. Thomas Kuhn, author of “The structure of scientific revolutions” wrote that there are long periods of normal science. In those periods there is a set paradigm within which science sees the world, and there are set ways in which problems can be solved. The problem of why hail should form was an anomaly to be solved within the existing explanatory framework, a framework that involved only inorganic material as cloud condensation nuclei. His professors ‘knew’ that only substances like salt from ocean spray, sand from the desert, smoke from fires, and pollution from factories could nucleate the water vapor in the air. To them, the understanding of rain was to be found in the province of high and low pressure systems, hot and cold air masses, vertical temperature profiles (so called lapse rates), it was to be found through understanding the impact of the sun’s radiation, and how land and ocean masses absorbed and transmitted heat. It was to be found in the province of the inorganic. Schnell had brought biology in to domains where they thought biology shouldn’t be involved. Biology was messier than the inorganic world - plants can die, grow, and replicate in different places. If biology was involved there were many more variables to take into account.

In the view of his professors, Schnell had unwittingly stepped outside the boundary of normal science. To these guardians of normal science he was a mere novice that didn’t yet know the existing paradigm, and so was treated with bemused chuckles. Now it is indeed useful to have guardians of normal science. This is because it protects against the propagation of false explanations and theories, lessens wasted effort, and often provides an efficient heuristic with which to do research. However the price is that it can make it difficult to find the truth when the truth lies outside the boundaries of normal science. The science where new paradigms are proposed, where original worldviews emerge, Thomas Kuhn called revolutionary science.

Schnell was either on the path of a false explanation, or he was on the path of doing revolutionary meteorological science.

To create a new paradigm, requires figuring out new sets of relations, new experiments, and new ontologies. Its often not just one conjecture that makes a paradigm, but a whole set of conjectures. Its not a simple matter to create a new paradigm.

Schnell thought about the known science of how cloud droplets were created out of the water vapor that was hovering high up in the air. There were two basic ways. One is when the water vapor nucleates into a liquid water. The other is when the water vapor nucleates into ice, and the ice then melts into liquid water.

Interestingly enough the water vapor will not automatically turn into liquid or ice at 0 Celsius (32 Fahrenheit). Instead it becomes supercooled. The water vapor will not actually turn into ice until -40 Celsius (which is also coincendentally -40F) if there are no particles to nucleate onto. When there are inorganic particles in the air, the water vapor will turn into liquid or ice somewhere from between -15 C to -40 C. Because usually up in the atmosphere there are little particles floating around, water vapor turns into clouds at temperatures higher than -40C.

A second bold conjecture could help clarify how organic matter might seed rain. The conjecture was that biological matter caused the water vapor to nucleate into ice at a higher temperature than inorganic matter could. In this way more ice forms than when there was just inorganic material, and that ice could turn into hail. This means the fact that there is biological matter in the air becomes quite important, for it will facilitate the formation of ice in temperature conditions that the non-biological matter can not. That’s why Schnell had noticed hail forms more often around forests and places with a lot of vegetation.

To test this, he wanted to gather matter in those places and see if there was some condensation matter they had that could condense at higher temperatures. The experiment was done by putting the liquid on a cold stage and lowering the temperature on it. He wrote “I collected fresh tree and grass leaves, washed them and tested the water for ice nucleating activity on the portable drop freezer Gabor Vali had at the hail studies facilities in Penhold. To my great surprise there were no active ice nuclei in the washes. Luckily, I neglected to throw out one of the sodden leaf batches. So, three weeks later I tested that sample; all drops froze near −1.5°C!!!” Because it froze at higher temperatures than was known possible for inorganically nucleated water, then that would suggest that biological matter was at work. Later he would repeat the experiment with aspen trees and the soil around them. He wrote “For fresh leaves, the formation of active freezing nuclei was found to peak roughly 3 weeks after collection. For fallen leaves, activity near −2°C developed within a week. Such activity developed only in samples exposed to air indicating a crucial role for aerobic microorganisms in INP (Ice Nucleating Particle) formation. In the well-decayed leaf litter, activity started near −4°C and reached a concentration of 10⁹ INPs active at −10°C per gram of material. The loam and clay samples contained considerably less active INPs.”

He gave the substance to someone at the university to study. The main protagonist that was nucleating the mixture turned out to be a bacteria, Pseudomonas Syringae. The bacteria has a certain pattern on its body, which caused water molecules to rearrange into an orderly array next to the bacteria’s cell wall, that then naturally led the water to crystallize into ice.

After graduation, Schnell entered the atmospheric science PhD program at University of Wyoming. He continued collaborating with Gabor Vali, a cloud physicist to present a theory of bacteria seeding rain at a conference on cloud physics in 1970, and then in 1972, they published a paper on the theory in one of the world’s premiere science journals, Nature.

Schnell was hot on the tail now, but he was short on funding. He wanted to see if the bacteria seeding phenomena was happening not just locally, but also around the world. He embarked on a trip to Europe, Asia, Africa to collect grasses and vegetation, while living on only $100 a month. Some days he barely ate.

To his delight, he found organic nucleation molecules that would freeze the water at higher temperatures all around the world. The bacteria were seeding rain everywhere. Schnell and Vali published the results, writing in a 1976 paper “Using numerous measurements from around the globe, atmospheric ice nucleus concentrations, and also freezing nucleus concentrations in rainfall, were shown to exhibit a climatic dependence similar to that of biogenic nuclei sources at the surface. This correlation suggests that large proportions of atmospheric ice nuclei are possibly of biogenic origin.”

…..

In Montana in 1978, without knowledge Schnell’s work, a plant pathology professor was also about to stumble upon the connection between bacteria and rain.

David Sands loved bacteria. In a Ted talk, he smiles happily, almost sheepishly happy, saying “I am a bacteriologist, I love bacteria, they can grow on a petri dish.” He is a professor who is frequently requested by farmers to help deal with infestations to their crops. Our food systems are billion dollar systems, and farms are constantly beset with different diseases.

One day he was called by a farmer in regards to ice damage to his crops. The cause - a particular bacteria called Pseudomonas Syringae. Sands looked the situation over, treated the crops, and killed all the bacteria. With methodical care, he scanned the leaves and soil for traces of the bacteria. None left.

But then the farmer called back three weeks later - there were bacteria again. What? - Schnell thinks - How could it be coming back? Sands hypothesized that the bacteria travelled through the atmosphere, blown by the wind.

He decided to test his hypothesis. Now some experiments are methodical, boring almost. This experiment, on the other hand, is more swashbuckling in nature. Sands rents a small Cessna 180 airplane, sticks his hand through the porthole while holding a petri dish. The plane circles, descends, turns back every 500 feet to collect bacteria at different altitudes. Sands wants to vomit.

The results come back. Indeed there are bacteria. And not only that, they find ice crystals, and in the ice crystals find the tiny bacteria enmeshed inside.

This gets Sands neurons churning. Sands says “Occasionally we get these hunches, or hypothesis, science calls them hunches, its some idea we don’t have enough data for”. His big hunch - the bacteria are nucleating the water vapor into rain. He knows the bacteria are good at creating ice, they can nucleate water at higher temperatures than normal - that’s why they create frost damage on plants. The bacteria have to find a way to get down from up in the atmosphere. What better way than to create rain to help it plummet to the ground.

……

In the 1980s, Colorado ski resorts learned of the bacteria seeding research, and they started pumping Pseudomonas Syringae into the air to create snow for their resorts.

…..

Progress on bacterial bioprecipitation after the breakthroughs of the atmospheric-science-oriented Schnell and the plant-pathology-oriented Sands was slow. Nothing much more happened for many years. This is not abnormal behavior for new paradigm research. New paradigm ideas often sit for a long time. That’s because the ideas are so new most people do not know what to do with them. Not knowing the larger worldview it is embedded in, there is less to orient to. You are walking in the dark with only a few scattered handholds. Its hard to move far. What experiments to do, what puzzles to solve, are not properly delineated. There is yet to be, what the philosopher of science Imre Lakatos called, a ‘research programme’.

Chaos theory sat for fifty years after Poincare discovered it, before anyone else made more inroads into the theory. His finding in 1903 that differential equations can have chaotic solutions was so bizarre, that no one knew how to apply general differential equation techniques to explore his results further. No one new what was the larger worldview his findings implied. It would take the onset of the computer age, half a century later, for an intuiton to build around chaotic equations. It was then that a whole new language emerged, a language of horsehoe attractors, fractals, Lyapunov exponents. And it was then that a whole set of archetypal systems would be delineated - double pendulums swinging unpredictably, butterflies flapping their wings to start hurricanes, predator-prey relations undergoing chaotic oscillations, and dough folding creating fractal manifolds.

It would take thirty years, for the bacterial rain-seeding hypothesis to get more traction, for the arrival of new archetypes of experiments that could show the hypothesis’s plausibility. It would take awhile for the language of positive and negative feedback loops, of climate regulation, of water cycles and precipitation recycling (small water cycle), of biogeochemical cycles, and of aerial microbiomes to intertwine with the original bacterial idea. It would not be until the 2000s that there would be workshops and conferences on bioprecipitation, bringing an interdiscplinary wave of interest to the topic, and funneling grad students and post-docs into the new discipline. It would take awhile til microbiologists sniffed out that their own specialty may play an important role in the distant field of climate science, and to then traverse across the scientific landscape, like pioneers, to create a new discipline - aerobiology. New questions arose - how did the atmospheric microbial ecosystem work? Was the microbiome multiplying and self-replicating in the atmosphere? How was the microbiome influencing its own transportation via wind and water vapor across the globe? It would take time for the seeding idea, to leap from just bacteria, to organic matter in general. Scientists would discover that fungi spores and lichen matter could seed rain also. And the fungi and lichen were not necessarily fully analogous to bacteria in their climatic ripple effects, they had their own distinct impact on the water cycle and temperature regulation.

A new microorganismic climate cosmology was afoot.

Read ‘Bioprecipitation part II’ here

Christner, B (2012) Cloudy with a chance of microbes Microbe

Constantinidou HA, Hirano SS, Baker LS, & Upper CD (1990). Atmospheric Dispersal of Ice Nucleation-Active Bacteria: The Role of Rain Phytopathology (80), 934-937 DOI: 10.1094/Phyto-80-934

Creamean, Jessie M., Kaitlyn J. Suski, Daniel Rosenfeld, Alberto Cazorla, Paul J. DeMott, Ryan C. Sullivan, Allen B. White et al. "Dust and biological aerosols from the Sahara and Asia influence precipitation in the western US." science 339, no. 6127 (2013): 1572-1578.

DC Sands, VE Langhans, AL Scharen, G de Smet, The association between bacteria and rain and possible resultant meteorological implications. J Hungarian Meteorol Serv 86, 148–152 (1982)

Hoose C, Kristjánsson JE, & Burrows SM (2010). How important is biological ice nucleation in clouds on a global scale? Environmental Research Letters, 5 (2) DOI: 10.1088/1748-9326/5/2/024009

Morris CE, Sands DC, Vinatzer BA, Glaux C, Guilbaud C, Buffière A, Yan S, Dominguez H, & Thompson BM (2008). The life history of the plant pathogen Pseudomonas syringae is linked to the water cycle. The ISME journal, 2 (3), 321-34 PMID: 18185595

Lundheim R (2002). Physiological and ecological significance of biological ice nucleators. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 357 (1423), 937-43 PMID: 12171657

Pratt KA, DeMott PJ, French JR, Wang Z, Westphal DL, Heymsfield AJ, Twohy CH, Prenni AJ, & Prather KA (2009). In situ detection of biological particles in cloud ice-crystals Nature Geoscience, 2, 398-401 DOI: 10.1038/ngeo521

Schnell, R., Vali, G. Atmospheric Ice Nuclei from Decomposing Vegetation. Nature 236, 163–165 (1972). https://doi.org/10.1038/236163a0

Vali, Gabor, and Russell C. Schnell. "Looking back: An account of how ice nucleation by bacteria was discovered (1963 to about mid-1980s). Part I: The basics." Bulletin of the American Meteorological Society 105, no. 4 (2024): E778-E788. https://journals.ametsoc.org/view/journals/bams/105/4/BAMS-D-23-0114.1.xml

Schnell, Russell C., and Gabor Vali. "Looking back: An account of how ice nucleation by bacteria was discovered (1963 to about mid-1980s). Part II: Broadening the scope." Bulletin of the American Meteorological Society 105, no. 6 (2024): E1004-E1014. https://journals.ametsoc.org/view/journals/bams/105/6/BAMS-D-23-0115.1.xml

Sesartic A., Lohmann U., & Storelvmo T. (2011). Bacteria in the ECHAM5-HAM global climate model Atmos. Chem. Phys. Discuss., 11, 1457-1488 DOI: 10.5194/acpd-11-1457-2011

Vali, Gabor, and Russell Schnell. "Contribuition of natural feezing nuclei to precipitation development” In Preprints of Papers Presented at the Conference on Cloud Physics: August 24-27, 1970, Ft. Collins, Colorado, p. 41. American Meteorological Society, 1970