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How Rain Forms Naturally: Pseudomonas Syringae

Susette has a Master's degree in Sustainable Development. She leads her local Green Council and writes for The Sustainable Business Review.

At the center of raindrops and hailstones lies Pseudomonas syringae - an ice-nucleating bacteria whose freezing action causes water vapor to condense into clouds, rain, hail, sleet, and snow.

At the center of raindrops and hailstones lies Pseudomonas syringae - an ice-nucleating bacteria whose freezing action causes water vapor to condense into clouds, rain, hail, sleet, and snow.


Nearly every "bad" thing has a counterpart "good" role and the bacteria. Pseudomonas syringae is no exception. For eons, agriculturalists have fought what they call "black speck" on tomatoes and other crops without realizing that the bacteria they thought caused it is a seminal creator of rain. In other words, we've been killing the precipitation-making bacteria so crops can thrive while simultaneously reducing our chances for rain, sleet, and snow.

Pseudomonas Syringae

During his graduate studies, Dr. Lindow, a plant pathologist at UC Berkeley, is credited with first identifying P. syringae as a biological ice nucleator in the 1970s. He discovered that the bacteria produces an "ina protein" (ice nucleation active) that causes water to freeze, which softens a plant's skin, so the bacteria can dig under it to suck its juices. But the freezing action doesn't stop there. Wherever the bacteria goes, it carries that freezing action with it.

P. syringae's ice nucleation ability helps make frost on plants.

P. syringae's ice nucleation ability helps make frost on plants.

Precipitation Studies

Recent studies by meteorologists and plant pathologists prove that P. syringae plays a crucial role in forming all forms of precipitation (raindrops, hailstones, and snow). In 1982 Russell Schnell, attending the University of Colorado at the time, noted that a tea plantation in Western Kenya was having hailstorms 132 days of the year. He discovered that the hail was forming around tiny particles carrying P. syringae that were kicked up by tea pickers in the fields.

How Rain Forms

In 2008, a microbiologist at Louisiana State University discovered that 70-100% of ice nucleators in snow freshly fallen in Montana and Antarctica were biological. In May 2012, a researcher at Montana State University found high concentrations of bacteria in hailstones that had fallen on campus. Based on this and additional evidence, scientists are now wondering if there might be an entire ecosystem of rain-making bacteria living and reproducing up in the stratosphere.

Most of the research so far has been carried out by plant biologists; however, their results are reviving the interest of atmospheric physicists. At least 30 scientists worldwide are researching bacteria's role in forming rain. They are speculating about the possibility of directing the fall of precipitation by deliberate production of known biological ice nucleators like P. syringae.

If the bacteria were "grown" in dry locations, wind would carry colonies high, where P. syringae could act as the coolant around which water vapor condenses into raindrops (or hail). Although rain also forms around dust motes, volcanic ash, and salt particles when it's cold enough, P. syringae cools vapor into precipitation at higher temperatures because of its ina protein. According to Dr. Snow at the University of Montana, a single bacterium can make enough protein to nucleate 1000 snow crystals.

Biotech Research

In what seems like another case of separatist specialization, agro-scientists have been studying the P. syringae strain that grows on tomato plants (from an agricultural point of view) to find out whether its constant recurrance, even after potent pesticide applications and the development of GMO tomatoes, shows an incredible ability to adapt, or if it's a completely different bacteria that shows up each time.

They decided that the bacterium mutates and adapts quickly to get around obstacles placed in its way. These scientists warn the world that, ". . . new pathogen variants with increased virulence are spreading around the globe unobserved, presenting a potential threat to biosecurity."

Healthy tomatoes unaffected by bacterial speck.

Healthy tomatoes unaffected by bacterial speck.

Bacterial Speck, as it's commonly called on the tomato plant.

Bacterial Speck, as it's commonly called on the tomato plant.

Their solution is to break down the "pathogen" even more, to identify its features more minutely, to find out where it came from, where it's spreading to, what can be done to interfere with the spread, and/or try to create tomatoes that are more resistant. Of all of these options, it appears to me that only the last one has validity . . . as long as the bacterial colonies can grow elsewhere.

Fortunately, there are many alternative plants for P. syringae to feed on. The tea plant is one of 50 others that agriculturalists have identified so far (tobacco, olives, beans, rice are others). The result of biological ice nucleators colonizing on tea is called "bacterial shoot blight disease," but the process is essentially the same as what happens with the tomato plant.

The P. syringae bacterium's ice nucleation activity causes water to freeze on plant leaves or fruit, so it weakens the protective cover, allowing the bacterium to burrow in, feed, and reproduce. This creates the same wet, weak, blackened spots on tea leaves and stems that it does on tomatoes. As the bacterial colony grows, many drop off into the soil, where they are stirred up by wind or by the feet of passing travelers or pickers - perhaps giving credence to the efficacy of rain dances.

Scientists have given each plant "pathovar" its own sub-designation (P. syringae pv. tomato, P. syringae pv. theae), but according to Wikipedia, they don't yet know if each pathovar is adapted to survive on only one type of plant, or if these are all the same bacteria that feed on many hosts. They all exhibit the same traits and are found throughout the world, both on the ground and in the air.

The same condition on other plants is called: Brown spot, halo blight, bacterial canker, bleeding canker, leaf spot, and bacterial blight, for those of you who recognize plant diseases.

Making Clouds

Although it still rains and snows, occurances are becoming more extreme and the locations more polarized - with over-heavy rainfall where physical conditions allow it and drought where they don't anymore. This could be partly because of reduced habitat for rain-making bacteria. In the past P. syringae could reproduce wherever it wanted to and create rain wherever it reproduced. That ability still exists, but the probability of it is much lower, as host plants disappear or are protected with pesticides. The following chart shows some examples of how human activity has decimated habitat for P. syringae:


Industrial agriculture's application of pesticides

Attempted to kill off P. syringae

All over the world

Industrial ranching

Destroyed grasslands that used to host bacterial colonies

Southwest & Central United States

Industrial ranching

Decimated thousands of acres of Amazonian jungle

Brazil, Argentina

Cut wood for firewood/housing

Destroyed forests, created deserts

North, east, and southern Africa

How can we enhance, or at least rebalance, Nature's ability to make clouds with a bacteria that our farmers despise? One good possibility is to pick a specific location—say an island—on the windward side of dry lands to cultivate the bacteria. Let it multiply on its favorite plant/s there and measure what happens when a good wind kicks up. Then look to see when and where it rains on the mainland nearby.

Upcoming Storm in Pasadena, California

Upcoming Storm in Pasadena, California

Weather Balance

Here is the ultimate goal: To have a balance of biomes in every continent with just enough rain to support them. For example, Australia could have green cities, a desert, a forest, grasslands, and seascapes, instead of being primarily a giant desert surrounded by ocean with a little forest up north. All of its citizens would have access to drinking water from groundwater, rainfall, and/or a giant lake in the interior.

Man would not be at the mercy of the weather, but would be able to predict when and approximately where precipitation would fall. There would be no more wars based on water scarcity (though maybe on other things). Palestine, Jordan, Pakistan would each have their own water sources, as would Israel and India.

Humankind would tip the scales from identifying Pseudomonas syringae as "bad" to recognizing the essential constructive nature of this rain-making bacteria and maybe many other things we've labelled "bad" as well. Where there's a bad, there's always a good. We need to look more often for the constructive, useful side of what we have too long called "pests."

Rain in Santa Fe, New Mexico - a normally dry part of the country.

Rain in Santa Fe, New Mexico - a normally dry part of the country.

The Future of Pseudomonas Syringae

Dr. Lindow continued his experiments with P. syringae, subsequently discovering a mutant bacterium he called "ice-minus" strain, that he then duplicated himself via GMO experimentation. When tested on several different crops, the mutant strain worked to prevent plants from frosting even during cold weather. This is good news for factory farms. However, for anyone depending on rainfall, including farmers, it may not be such good news. If the strain competes well enough with P. syringae to drive it out, it could create serious problems with the weather.

Cold weather frosts and bacterial ice action do destroy crops, but crops cannot survive at all without the rain and snow generated by ice-nucleating bacteria. Continued experimentation is crucial to increase our understanding of the role P. syringae plays within the hydrologic cycle, and to find out how we can enhance, rather than destroy, its ability to create rain where it's needed.

Bus on a rainy day in Albuquerque. Look for evidence of P. syringae and start pointing it out to people. We need this awareness to spread.

Bus on a rainy day in Albuquerque. Look for evidence of P. syringae and start pointing it out to people. We need this awareness to spread.

For More Information:

Questions & Answers

Question: Is Pseudomonas syringae used today to make rain?

Answer: Yes. There's a company in Denver, CO, that produces a product called "Snowmax" ( made from the ice nucleating proteins contained in P. syringae. It kills all the living bacteria so they don't reproduce and create a stronger effect than customers want. Their customers are mainly ski resorts.

Question: Can bacteria like Psuedomonas Syringae have any practical use?

Answer: Probably, although it seems like directly cultivating them, so they can produce rain in specific areas that would be pretty practical. Actually, it turns out that some ski resorts are using dried bacteria to produce more snow for their ski slopes. Further, once meteorologists figure out how to do it, the bacteria could be used for everything that silver iodide is used for now: Cloud seeding to turn hailstorms into rain, possibly reduce hurricanes (by making it rain sooner, so the clouds don't build up so high), prevent floods and water deserts by balancing the locations in which it rains. The question is whether they're willing to do the work to figure out how, or just keep doing the easy thing of using silver iodide. Did you read my article on cloud seeding, perchance?

Question: Is there is any practical application of Pseudomonas syringae to reduce drought?

Answer: Yes, but only in small projects at this time. Many ski resorts are spraying cultivated and dried P. syringe into the air around their resorts to trigger snowfall. It works, but the process is more tedious for larger applications than making silver iodide sprays. Meanwhile, I noticed a graduate student at MIT is setting up an experiment similar to what I speculated in this article, to be conducted somewhere in the United Arab Emirates. She listed my article at the end of her application, along with several others.

Question: We are having a drought at this time. Could Pseudomonas be used for a storm seeder in the Western Pacific so that the storms would carry across to the West Coast?

Answer: First of all, P. syringae is the proper name of the bacteria. Pseudomonas is the name of a whole genus covering many different species of bacteria. Second, you may have noticed we're not in a drought anymore on the West Coast. We're entering the second week of rainstorms that may extend into a third week as well.

However, I do understand your question and have speculated on that possibility myself. As with other experiments with cloud seeding, it would need to be tested before any extensive use, to make sure we don't inadvertently overdo it and cause massive flooding. Read this article for more information about cloud seeding, including the possibility you bring up.


Susette Horspool (author) from Pasadena CA on January 29, 2020:

Like most bacteria, it reproduces by binary fission, which is to say that it splits itself in half when the conditions are right.

Keagan on January 28, 2020:

How does it reproduce?

Susette Horspool (author) from Pasadena CA on February 24, 2016:

Hi Eman - Thanks for reading. In the article I provided links to four key sources of information I used. Which particular "scientific information" were you looking for? (BTW, note that I have a masters degree in environmental issues, and that background is one of my resources.)

eman on February 23, 2016:

If allowed I would like to know the source of which derived scientific information

Susette Horspool (author) from Pasadena CA on July 25, 2015:

Thank you all. New (or secret) information always fascinates me and I'm glad my writing conveys that. I'm reading a book called "The Secret Language of Plants" that is filled with great information, including how trees create their own ecosystems and encourage certain types of bacteria to make themselves at home.

Bacteria are in many ways our ancestors, having dominated the earth before us. They help create healthy environments, including our own bodies inside. They become a problem only when an ecosystem gets out of balance (which humans are notorious for causing) and one type of bacteria dominates to the point of illness or we lose the benefits of a type that is disappearing - like Pseudomonas syringae.

Marlene Bertrand from USA on July 24, 2015:

Fascinating! You have a way of writing that makes science interesting. I really enjoyed reading about Psudomonas syringae. Congratulations on receiving the Hub of the Day award.

stella vadakin from 3460NW 50 St Bell, Fl32619 on July 24, 2015:

This was very interesting and have never really thought about a bacteria that could be good. I think people need to understand the issues. congrats on HOTD. Stella

Kristen Howe from Northeast Ohio on July 24, 2015:

Susette, congrats on HOTD! This is a most fascinating hub on rain formations. Voted up for interesting!

Arun Dev from United Countries of the World on July 24, 2015:

You've shared wonderful information through this hub. This is another way through which bacteria can affect Nature. Voted up and congrats on HOTD.

Mazlan A from Malaysia on July 24, 2015:

Congrats on HOTD on this well researched and written article on pseudomonas syringae. It is interesting to know how this rain making bacteria has been destroyed by mankind - sad, but man like to label 'bad' as bad without understanding the issues :-(

Susette Horspool (author) from Pasadena CA on October 01, 2012:

I was so excited when I first saw this study, Sid! I kept thinking about how cultivation of this bacterium could help counteract global warming. Rain cools and cleans the air and earth, so if we could somehow encourage rain to fall more evenly around the world, everything could change.

Sid Kemp from Boca Raton, Florida (near Miami and Palm Beach) on September 30, 2012:

This is absolutely fascinating, and an amazing breakthrough of a discovery, as well. We know that the oxygen in our atmosphere is a result of plant life, and that the current level (21%) is a result of a balance of animals and plants. (When it gets up to 25%, as it did before there was much animal life, we had continent-sized wildfires - not very comfortable!)

But this is the first that I've heard of a biological effect on local, current weather. That changes our whole picture of the biosphere, as now there is a direct link between the current status of it's non-living elements (water, rain, humidity, moisture, fresh water on earth) and its living elements with the living shaping the non-living in a very big way!

Susette Horspool (author) from Pasadena CA on September 08, 2012:

That's what I'm thinking, Leah. And you know what? I just did a little fun search on my name "watergeek" and discovered somebody using the same name who's a forest hydrologist in Amsterdam - a university professor teaching the next generation about hydrology. He invited me to join his Hydrology International group and could be a really cool resource for exploring that very possibility!

Leah Lefler from Western New York on September 08, 2012:

This is really fascinating, watergeek. The ability of a bacteria to form ice crystals (and an "ice-minus" version that is able to protect crops from frost) is really interesting. Maybe it would be worth a few black specks on our crops to increase the chances for rain!

Susette Horspool (author) from Pasadena CA on September 06, 2012:

That's an interesting speculation. I have no idea what is in volcanic ash. I do know that the ash is one component scientists have found rain forming around. Thanks for commenting.

whonunuwho from United States on September 06, 2012:

This is a fascinating hub on this bacteria and I wonder if the source might be from volcanic ash thrown into the atmosphere from time to time and coming back down in rain or ice crystals? This would seem to me be a likely source and there are volcanoes erupting around the globe periodically. Thanks for your interesting article, and well presented.