Prokaryotic Saturday: tales of a glowing bacteria

Today is Saturday and it is also the first Prokaryotic Saturday of this blog!!! Yeyy!

So, today I want to talk about this little crazy guy called Vibrio fischeri.

I won’t say anything new, so if you already know what this guy does, then you can safely stop reading this post………………………… Now that I have that part of the audience that does not know or it is just too bored and doesn't have anything more interesting to read, let me continue. V. fischeri is a gram negative bacteria, which lives in the mantle of the hawaiian bobtail squid. This bacterium is the proud owner of the “canonical quorum sensing system”. It is called 'canonical' because it is by far the most studied and the best described system, since this one was the very first quorum system ever discovered (around 1980, by Nealson et al.).  

You might be wondering what does “quorum sensing” mean. Well, quorum sensing is when bacteria modify in some way the expression of their genes depending on the amount of other bacteria in the medium (cell density). It is believed that bacteria are able to “talk” using chemical signals, not only with other bacteria of the same species but also with organisms of other kingdoms. It’s like when you go out by yourself, you can have a good time of course, but definitely it is not the same when you go out with your friends. And the more you are, the more fun it is. Same here, the more bacteria there in the medium the more behavioral changes they express.

Although the topic of this Prokaryitic Saturday it is not quorum sensing (I probably talk about it later), you can visit Dr. Bonnie Bassler webpage (or just google her name) and learn more about this amazing and tremendously interesting field.

Now, for some reason I feel this post is already getting boring. So, let’s go back with the V. fischeri. This bacterium lives in the mantle of the hawaiian bobtail squid as I just told you. And when you isolate it in the lab you can create some funny stuff like this petri dish:

Because V. fischeri is a bioluminescent bacteria, it glows in the dark, and you don’t have to do anything. :o 

But how does this happen? Here is when the quorum sensing thing comes into action. This bacterium can glow thanks to the expression of two genes, luxR and luxI. These genes are part of the operon luxICDABE. These two genes, luxR and luxI produce two proteins, proteins LuxR and LuxI (yeah, people were not very creative here). And protein LuxI triggers the synthesis of an autoinducer, the homoserine lactone molecule (HSL). So HSL accumulates in the intra and extra cellular environment, and as the number of cell increases, so does HSL. And when concentration of this autoinducer reaches something around 10 ug/ml, HSL binds protein LuxR, then this complex (LuxR-HSL) binds to the operon luxICDABE and bang!!! Genes express and cells glow like crazy!! woooww!!!

Isn’t this cool?

But now, don’t you wonder why? I mean, a glowing bacteria? Why is this crazy bacteria producing light? Maybe she just like showing off.

Well, actually not. There is a good reason and it is the same reason that explains most of animal's behaviors (other than human): survival.

   

The squid, which is the home of V. fischeri, uses this bioluminescence to hide from predators in a very clever manner. This squid (Euprymna scolopes) hunts at night, and uses the light emitted by V.fischeri to simulate the moon light and hide its shadow. The next video of Dr Siouxsie Wiles (@SiouxieW) explains it better. But the thing is, V.fischeri gets food from the squid, and the squid gets an “invisibility cloak”. Plus other few thing, like this light emission mechanism also help the squid to attract predators and mates. So, it's a win-win. 

Now, you can’t say this is not cool.

So that is it. First Prokaryotic Saturday went well, I think. Although you can find many animations and videos online about the LuxI/LuxR gene regulation process, I have a very cool animation (which I created, hehe) so email me if you want to see it, I will send it to you (for some reason I couldn’t upload it here, sorry). And if you have any questions or suggestions, please, leave them in the comments or at @ale_alvarador. 

See you next week!