Rain making Microbes

New research show that microbes, especially bacteria and now fungi are the best at pulling moisture from the sky and making it rain. Dust and dirt particles can help it rain, but they are not as efficient as microbes.

A recent article in Science Advances shows how the rain cycle works. Most rain starts as atmospheric water vapor and has to freeze into ice crystals before it comes down, turning into rain. Water in the atmosphere does not always freeze at 32OF. In fact, atmospheric water can stay liquid down to -40OF below zero. Temperatures are much lower at cloud level so clouds can stay full of moisture till it gets cold enough and attaches to something to freeze to cause ice crystals and then turn to rain. “Supercooled” water is a liquid cooler than normal freezing water because it has nothing to hold onto.

For clouds to make snow, ice, or rain, it needs a “seed”, a tiny particle for the water molecules to grab onto to form an ice crystal before it falls from the sky as rain. Dust, soot, and salts can be a “seed” to make ice crystals, but they are not very good at it. They need really low temperatures to form ice crystals. So that is where biology in the form of microbes and ice forming proteins help make the formation of ice crystals and ultimately rain more efficient.

Scientist have known for some time that ice producing proteins in the atmosphere help “raise the temperature” you might say, so that ice crystals form easier. Pseudomonas bacteria form this ice protein but now scientist have discovered that beneficial fungi also make this protein. Through evapotranspiration (movement of water vapor from land and plants to the atmosphere), microscopic bacteria are transported into the atmosphere where they can live and trigger it to rain much closer to the actual freezing point of water. This is a good thing. It lets water vapor escape the atmosphere in smaller doses or more often. As farmers, several 0.5 to 1 to 2-inch rains are much more appreciated than 3 to 5 to 7-inch rains or more.

The fungi Fusarium and Mortierella also secrete this special rain making protein into the soil around where they grow. The fungi structure allows them to make water proteins that are smaller than the bacteria proteins and water soluble and with a much higher temperature for forming ice crystals. That means it can rain easier, maybe a little more often, but not the downpours we are starting to see more often. Fungal water-making ice proteins are the best, followed by the pseudomonas ice proteins and then a very distant third are the dust, soot, and salts. Scientist say that we have a bio (living) precipitation cycle that is much more highly efficient at making rain.

Imagine a forest of fungi with rain making proteins picked up by the wind. It could also be a living cover crop covering a field of corn stalks or soybean residue. The microbes in this vegetation live and thrive on live plants which helps keep the rain cycle operating effectively. Once in the air, these ice making proteins become powerful seeds for making it rain more naturally and more frequently with less intense destructive rainfall events. Have we changed that natural cycle in the last 50 to 100 years?

On a related note. People can often sense it is going to rain. This “pre-rain” smell comes from ozone formed when oxygen (O2) in the atmosphere is spilt through electrical charges in the clouds to form ozone (O3). Ozone is blown down from the upper atmosphere and has a sharp odor, somewhat like chlorine or burnt wires. This pre-rain smell is a good indication a storm is brewing before the pleasant smell of rain occurs.

The smell of rain is caused by soil actinomycetes. Scientist have a name for it called petrichlor (pronounced pet-try-cure). As rain infiltrates the soil, it causes the actinomycetes to form spores which are released along with geosmin, a chemical that creates that earthy soil smell when soil is tilled. Geosmin and petrichlor are especially more intense in healthy soils, due to higher soil microbial activity. Healthy soils have more oxygen and have a sweeter aroma due to healthy microbes.

Geosmin boosts certain chemicals like serotonin and norepinephrine in your brain which act like antidepressants. Rain on healthy soils may decrease stress and improve your mood by 60%. The human nose can detect geosmin at 5 part per trillion or very low levels. That’s why a good rain can be so refreshing to human mental health and is related to healthy soil microbes.