After launching our website on World Microbiome Day, the next international event is coming up: International Microorganism Day on September 17th. Another day, another mission? Yes and no. As the existence of two separate days with different names might be confusing, let’s fresh up your mind on microbial definitions. We also explain how you can contribute to International Microorganism Day.

By the UNLOCK team / September 14, 2021


Microbe, microorganisms, microbiota, microbiome… Interestingly, the terms used are as diverse as the microbial world itself. In fact, microbes are the same as micro-organisms and include bacteria, archaea, fungi as well as other microeukaryotes. Literally, micro-organisms are microscopic (micro- is derived from the Greek word for “small”) organisms, which means that they can be considered living. Therefore, viruses are technically not microorganisms, because they need a host cell to replicate. 

From microbe to microbiota

All microbes in an ecosystem, such as the soil or the intestinal tract, are collectively called the microbiota. Additionally, if you add up the conditions in the ecosystem, the compounds produced by the microbes and other structural elements, such as viruses, you end up with the microbiome. Still, although the terms mean something different, World Microbiome Day and International Microorganism Day share the same mission, namely celebrating the power of microbes.

About International Microorganism Day

International Microorganism Day was launched  in 2017 in Portugal. The date of September 17th was chosen, because this marked the day that microbiologist Antonie van Leeuwenhoek sent a letter to the Royal Society of London, in which he was the first to describe a single-celled organism, which happened in 1683. As stated on the website, the organization “aim(s) to teach and provide a platform, both online and offline, for microbe lovers around the world to share their passion and knowledge of the microbes in our daily lives.” Currently, four year since its launch, International Microorganism Day has multiplied exponentially and, moreover, spread internationally.

Banner of International Microorganism Day
Official banner of International Microorganism Day. Source:

How to celebrate

Starting already September 16th, the team of International Microorganism Day organize a 24-hour livestream, including lectures, workshops and also fun activities. This livestream can be accessed via the IMD-website or their social media channels. If you want to join, please find the detailed program here.

Interesting links

In case you cannot join IMD, but do want to get inspired by their mission, check out their education resources and blogs. If you want to read more on microbial definitions, read the paper below, which was published last year by, amongst others, Hauke Smidt:

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