How Does Rain Form: Pseudomonas syringae
Nearly every "bad" thing has a counterpart "good" role and the bacteria, Psudomonas syringae, is no exception. For eons agriculturalists have fought what they call "black speck" on tomatoes and other crops, without realizing that the bacteria that causes 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.
Dr. Lindow, a plant pathologist at UC Berkeley, is credited with the first identification of P. syringae as a biological ice nucleator in the 1970s, during his graduate studies. 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.
Recent studies of meteorologists and plant pathologists are proving that the bacteria plays a crucial role in the formation of 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 gathered, 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 currently researching the role of bacteria 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. A single bacterium, according to Dr. Snow at the University of Montana, can make enough protein to nucleate 1000 snow crystals.
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 reccurance, 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."
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 there is other food that will let the bacterial colonies thrive.
Fortunately, there are many alternatives. The tea plant is one of 50 other host plants 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.)
- Research Team Unravels Tomato Pathogen's Tricks of theTrade | Seed Daily
Blacksburg, VA (SPX) Nov 09, 2011 - For decades, scientists and farmers have attempted to understand how a bacterial pathogen continues to damage tomatoes despite numerous agricultural attempts to control its spread.
- Pseudomonas Plant Interaction
Chart of plants on which P. syringae is commonly found, along with the "disease" names.
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
Destroyed grasslands that used to host bacterial colonies
Southwest & Central United States
Decimated thousands of acres of Amazonian jungle
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.
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. 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."
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 precipitation 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.
For more information:
- The Long Strange Journey Of Earth’s Traveling Microbes | Yale Environment 360
Airborne microbes can travel thousands of miles and high into the stratosphere. Now scientists are beginning to understand the possible role of these microbes — such as bacteria, fungal spores, and tiny algae — in creating clouds and rain.
- Tracing Snow and Rain to Bacteria That Dwell on Crops | New York Times
The bacterium pseudomonas syringae, a living organism that freezes at higher temperature, serves as the nuclei for raindrops and snowflakes.