microbial ecology baas-becking hypothesis microbial community structure soil community structure

Find Me Where the Wild Things Are

Take a minute and think - what do you consider “wild things”? Would bacteria count in your book? Click to explore the tiny world of microbes and learn about some fundamental microbial ecology!

image alt text

Fig. 1 “Where the Wild Things Are” (Source: Maurice Sendak, 1963)

Hey guys,

The song “Wild Things” by Alessia Cara inspired this post. Why? Well, other than the classic children’s story of a little boy playing with monsters, this song reminds me of all the types of organisms that my colleagues and I study (or “play with” if you will) in biology. So I have to ask, what would you consider wild things?




For me, it’s microorganisms.

I bet I know what you are thinking: “Hang on a second, how are microbes… ‘wild things’? Aren’t they just a bunch of tiny, random cells?”

Now, maybe you realize some microbes make you sick (Chipotle anyone?), some help you digest food (the microbiome), and some are used for making everyday items (cheese, beer, and biodegradable plastics). But viewing bacteria on the same level as “lions, tigers, and bears” is just strange to think about, right? The truth is microbial life is vast and they have communities and ecosystems just like the rest of life… you just have to look a little harder to find these wild things. The field that investigates this is known as microbial ecology, the study of microorganisms interacting with each other and their environment.

So today I want to take you to my small world, focusing on an argument that I was first taught in microbial ecology:

alles is overal:maar het milieu selecteert

Translation: “Everything is everywhere, but the environment selects.” Since 1934, when Lourens Baas-Becking wrote this famous hypothesis, debates about it have ensued; we have been talking for 82 years! Why has this been such a hot topic for so long?

Well as we discussed earlier, microbes are not typically thought of at the same level as macroorganisms (mammals, birds, fish, etc.). Macroorganims can clearly be seen in environments – you’d know if you saw a polar bear, wouldn’t you? Bacteria are tougher to see. In fact, we still struggle in the 21st century to detect what is present in our water and soil despite being able to look at bacterial DNA “fingerprints” known as 16S rDNA. This inability is known as a “detection limit”. For example, let’s say we have two species: “A” and “B”. If there is one bacterial cell of “A” among hundreds of cells of “B”, you won’t be able to see the DNA fingerprint of “A” in your sample because it is not abundant enough for you to pick up. Since microbiologists are limited by the methods and technology available, it’s tough to tell who’s where and why on a global scale.

For those in support of the Baas-Becking hypothesis, it is thought that all microorganisms are everywhere on earth. This is also known as “microbial cosmopolitanism”. The reason you see different amounts of bacteria (and some below detection) is whether or not the environment makes the bacteria happily grow. So that one “A” bacterial cell among the hundreds of “B” cells may be because it can’t function as well in that particular environment. If you switched the environment to be more favorable for “A”, then that bacterial species would have a larger amount of cells while the “B” species would be too few to see. The point is though that “A” and “B” are present in both environments, but at different concentrations.

For those against the hypothesis, microorganisms are limited by dispersal, or spreading, around the world and such spreading is by chance. Environment still plays a role in activity once the bacteria gets there, but it is not the sole reason you see microorganisms in greater or lesser amounts. The reason why the “A” bacteria species is not detected in your sample could be simply because it never made it to that environment.

Now that you know both sides of the debate, I am going to leave it up to you. What do you think? Is everything everywhere or are there dispersal limitations for microbes like you see for macroorganisms? Please leave questions and comments below. The debate has been going for 82 years. We might as well keep it going, right?


[1] De Wit, Rutger, and Thierry Bouvier. “‘Everything is everywhere, but, the environment selects’; what did Baas Becking and Beijerinck really say?.” Environmental microbiology 8, no. 4 (2006): 755-758.

More From Thats Life [Science]

Dialogue & Discussion