Hello and welcome to Microbe Monday! I hope today finds you well. This is a short one as I have been extremely busy lately. This is my last week of work before I get a month long break, though, so yay!

You have probably at some point noticed the distinctive earthy smell that happens after rainfall, especially quick showers or in areas with lots of dirt. This scent has a microbial origin, and a diverse one at that! It's sometimes simplified as just being geosmin, but it's actually a complex of many, many different microbially-produced aerosols.

When raindrops hit porous surfaces like soil, they form a ton of little bubbles inside, which grow before releasing and popping. These bubbles shoot upwards quite quickly, and in the whole process pick up whatever random chemicals and microbes they run into in the soil.

Among them are the well-known geosmin, a chemical produced by many, many microbes, most notable actinomycetes and blue-green cyanobacteria. Geosmin is a bicyclic aldehyde and all-round simple fella. We can detect it at very, very low concentrations, so it tends to be a big contributor to the smell of petrichor. It also contributes to a large number of "off tasting" water and fish although it is a harmless chemical. It also is one of the major flavor chemicals of beetroots.

Another big contributor are plant oils they secrete during dry spells to help them survive the osmotic stress. These fall into the soil with time and likewise get picked up by raindrops. Some ozone can also be deposited by lightning strikes.

Additionally, and critically, this process picks up soil microbes too, and sends them flying away to parts unknown. Many microbes take advantage of phenomena like this, such as sea spray, to launch them into the air as a means of transit, riding the wind til they make it to new places, or even doing so consistently for long periods as a lifestyle! Microbes that do this are called aeroplankton and I love them.

Thank you for reading this Microbe Monday. Remember the wind lives!