Evolving Sience: Pseudomonas Syringae Bacteria Can Cause Lightning and Thunder

Everybody knows what causes thunder and lightning. In recent decades though, some biologists and atmosphere physics have challenged the current notion. They mean that bacteria are contributing to this phenomenon.

By Nils-Ola Holtze, Swedish retired surgent, stationed in Portugal

For precipitation (rain, snow, hail) to form, water must aggregate in clouds and become heavy enough to fall. For this to happen, at least in temperate parts of the world, ice crystals must form.

The water in clouds is in a supercooled state and doesn’t freeze until circa -36 degrees Celsius. To form clouds in the first place water must have something it can attach to, a cloud condensation nucleus. This can be small aerosols, dust, or soot particles. It can also be a microorganism such as a bacterium.

Pseudomonas Syringae

Many microbes have a special surface protein that can arrange water molecules to form ice crystals at relatively high temperatures.

One of those is Pseudomonas Syringae. These little bacteria can form ice crystals at much higher temperatures than inorganic particles in clouds. To do this it uses its surface protein to arrange water molecules in a crystalline form and can thus form ice crystals in such ”high” temperatures as -2 degrees Celsius.

As a curiosity we use this surface protein in our snow cannons, to save energy and water. So, there could be as much as a 30 degrees difference when ice forms (and thus the capability to precipitation) between a cloud with or without these ice-nucleating microorganisms.

Pseudomonas Syringae is considered a pest and it uses its ice-nucleating ability to crack open the leaves of plants to access nutrients and is causing lots of damage to our agriculture. Anyway, when it’s full, the light bacterium is swept up by the winds to the clouds where it again uses its ice nucleation ability to get heavy enough to fall on new hunting grounds.

A pioneer in the discovery of this cycle was David Sands, some 35 years ago. Since then, scientists have identified more than 300 different microbes with this peculiar ice nucleating activity.

Scientists are reasoning like this: lightning is an electrical discharge. Electrical voltage builds up in the clouds by colliding with ice crystals and water droplets. The formation of ice crystals is facilitated by bacteria in the clouds. At least theoretically, microbes could contribute to thunderstorms!

Another advantage to the bacteria would be that lightning is a significant contributor to fixating nitrogen, which is essential for many of the plants they feed on.

So, who makes the thunder? Thor, the son of Odin and God of thunder, the sky, and agriculture, or Pseudomonas? Maybe both, perhaps Pseudomonas is Thor’s little helper? As a Scandinavian I put my money on Thor, but who knows?

You can read a lot more about this fascinating subject under search words such as bioprecipitation, ice nucleating activity. And of course, Norse mythology.

Properties of lightning

Nitrogen fixation: Lightning breaks up nitrogen N2 molecules in the atmosphere so it can oxidize to NO. Ozone (O3) is also produced by lightning bolts and can oxidize Nitrogen (NO) to NO₂ (nitrogen dioxide).  The total production of nitrogen oxides by lightning is about 15 million tonnes per year, and plants just love it as a fertilizer.

Heat: Lightning can be up to 50,000 degrees Fahrenheit. To compare the surface of the sun which is around 11,000 degrees Fahrenheit.

Firestarter: Lightning strikes with about 3,000,000 flashes each day around the world. It causes thousands of wildfires which can cause much damage, but it is also necessary. Many plants are pyrophytes and can only reproduce after a fire.

Evolution of bacteria: Scientists routinely use electricity to increase the permeability of bacterial cell membranes to facilitate the inserting of DNA. This process is shown to already exist in nature. When lightning hit the ground, it facilitates the exchange of genes among soil bacteria.

To produce all lightning bolts on his own. Thor, The God of thunder, must swing his hammer about 3 million times each day.

Are we Killing the Rain?

Plants living in cold climates are quite resistant to frost. They have different antifreeze proteins that protects them and helps them survive in cold climate. These proteins prevent ice to crystalize in their organic fluid matter. Other species like fish and insects have also developed this strategy to survive the cold.

We use fish antifreeze protein in low-fat ice cream to prevent recrystallization, thereby maintaining a soft, creamy texture (sorry vegans).

Another use of antifreeze proteins is in medicine to improve the quality of sperm and ovules stored in a frozen state. Despite this ability to fend off ice crystallization down to -14 C, we can often see widespread frost damage in much higher temperatures than the plant normally survives in.

Guilty to this damage is often Pseudomonas syringae. These bacteria have a special surface protein that allows them to crystallize water to ice in such high temperatures as -1.8 C. The freezing causes damage to the plants’ skin and the bacterium can feed on the nutrients inside.

Pseudomonas syringae is considered a plant pathogen and causes damage to a wide range of crops. Farmers lose billions every year due to this bacterium’s behavior. To protect the crops, we try to eradicate Pseudomonas S.

Different methods are used to get rid of it. The most common way to kill it is by bactericides like copper compounds and other heavy metals. Sometimes antibiotics like streptomycin are used. Gene-modified strains without the ice nucleating capability have been tried, as well as breeding plants for resistance. Even some more sensible methods with strict hygiene and pruning are practiced.

You can see its bravery in the way it transports itself between different food stations. Swept up by the wind they act like cloud condensation nuclei to catch water and form clouds, then use its ice nucleating ability to get heavy enough to fearlessly fall thousands of meters back to terra firma.

Remember, for precipitation (rain, snow, and hail) to happen, at least in the temperate regions of our planet, ice must form. And the ice must grow and get heavy enough to fall. It seems like these bacteria are important rainmakers!

So, in our effort to eradicate Pseudomonas, and as we use more and more arable land, Are We Killing the Rain? Maybe we should be nicer to this cunning little creature?

By Nils-Ola Holtze