Microbial world in raindrops

As monsoon season has finally hit the grounds of Mumbai, the idea of writing an article on rainfall and the microbes in it hit my mind. Every time it rains, one of the most common questions I ask my youngest sister is “What makes the soil smell wonderful as soon as it becomes wet due to rain?” When I asked her this question for the first time in my life, she had a curious approach to try and find an answer to it. Still, now that she knows the answer to it, every year I ask her the same question without fail, she smiles and answers in an annoyed tone because, to date, she has already answered the same question about a thousand times. Yet, as an elder sister and an oath keeper of the ‘Elder sibling club annoying younger siblings for life’, I never fail to throw the same question at her every year! So this question was the reason today’s article idea popped out in my mind. Considering that it is her birthday today and coincidently Mumbai got its first rainfall today, I dedicate this article to her. So without any delay, let’s begin to soak in the wonderful weather and get inquisitive about the microbial world in raindrops.

When we think about raindrops, we often imagine them as simple droplets of water falling from the sky. However, each tiny droplet harbors a hidden world teeming with life. So far, we all know that microbes are present everywhere- right from the screens you are looking at, to the farthest thing you see, microbes are present everywhere. And thus, raindrops too have microbes! As surprised as you may seem now, it is a fact. The microbial world within raindrops is a fascinating and complex ecosystem that plays a crucial role in various environmental processes. In this article, we'll explore the science behind these microscopic inhabitants, their origins, and their significance to our planet.

What Are Microorganisms in Raindrops?

Microorganisms are microscopic life forms that include bacteria, viruses, fungi, and algae. These organisms can be found in virtually every environment on Earth, including within raindrops. As raindrops fall from the sky, they form around particles in the atmosphere and collect a diverse array of microbes from the air. Not to mention raindrops are a product of condensed water vapors travelling in the sky right from Earth.

How Do Microorganisms Get Into Raindrops?

Microorganisms enter the atmosphere through various processes such as wind erosion, volcanic eruptions, sea spray, and human activities. Once airborne, these microbes can travel vast distances, sometimes even across continents. When water vapor in the atmosphere condenses around dust particles or other aerosols, it forms raindrops. These raindrops then collect and carry the microorganisms as they fall to the ground.

Types of Microorganisms Found in Raindrops

1. Bacteria: Bacteria are one of the most common microorganisms found in raindrops. They can survive in harsh atmospheric conditions and are known for their ability to form spores, which are highly resistant to environmental stress.

2. Viruses: While viruses cannot reproduce outside their host cells, they can attach to aerosols and be transported by raindrops. Some viruses found in raindrops are capable of infecting bacteria, plants, and animals.

3. Fungi: Fungal spores are lightweight and can easily become airborne. These spores can be carried by raindrops and contribute to the dispersal of fungi across different environments.

4. Algae: Certain types of algae, particularly those that form cysts, can be found in raindrops. These cysts can survive the journey through the atmosphere and germinate when they reach suitable environments.

The Role of Microorganisms in Raindrops

We often think that rain is only responsible for life on Earth, but there are a number of minute phenomena that occur due to rain.

1. Nutrient Cycling: When raindrops containing microorganisms fall to the ground, they introduce these microbes into soil and water ecosystems. Many of these microorganisms participate in nutrient cycling by breaking down organic matter and recycling essential nutrients.

2. Atmospheric Processes: Some bacteria in the atmosphere can influence cloud formation and precipitation. For example, certain bacteria can act as ice-nucleating agents, promoting the formation of ice crystals in clouds, which can lead to rainfall.

3. Plant Health: Rain can transport beneficial microbes to plant surfaces and soil, enhancing plant health by promoting growth and protecting against pathogens. Conversely, it can also spread plant pathogens, impacting agricultural productivity.

4. Global Dispersion: Raindrops facilitate the global dispersion of microorganisms, allowing them to colonize new environments and contribute to microbial diversity across different ecosystems.

Conclusion

The microbial world within raindrops is a hidden yet vital component of our planet's ecosystems. These microorganisms play essential roles in nutrient cycling, atmospheric processes, and plant health, while also influencing human health and environmental monitoring. As we continue to explore this microscopic frontier, we gain a deeper understanding of the intricate connections that sustain life on Earth. So, the next time you feel a raindrop on your skin, remember that it carries a hidden world of microscopic life, each droplet a tiny ecosystem contributing to the grand tapestry of our planet.

Last but not least, to answer my previous question: "What makes the soil smell so wonderful after a rain?" - As the rain hits the ground and dampens the soil, a microbial species known as actinomycetes starts to awake and create a byproduct called 'Geosmin' which contributes to the 'wonderful earthy smell of the soil during monsoon'.

PS: Thank you my cri-sis, Biology sister Ketki for being an inspiration for this article. If you hadn’t opted for biology, and I hadn’t asked you the same question about the reason for the smell of the rain-soaked soil, this article wouldn’t exist today. Happy Birthday!

Thank you for reading! Happy monsoon :)

- Rachna Jadhav

@theresilientresearcher