I am a big fan of all the research about how bacteria interact with each other and also with us. This is why my first article in this blog was about how bacteria kill their enemies. However, this article is supposed to show you that bacteria can also help each other when circumstances require them to.
Recent research showed that two bacterial cells can form so called nanotubes between them with which they can exchange cellular content. This can include:
- exchange of DNA – which is how bacteria “learn” new abilities, for example the ability to survive the flood of antibiotics
- exchange of chemical molecules – which is how bacteria “talk” with each other and know that they are not alone
- exchange of nutrients to ensure the receiving cell survives
All of the three points are super interesting and deserve their own article at some point, but here I would like to talk about the third concept of how bacteria feed each other.
First let me explain some key words.
Proteins come in all shapes and sizes, are present in every cell and they are responsible for cellular activities. This means, some proteins are enzymes that make or break down cellular structures, they do cellular respiration or they are transporters that transport things in and out of the cell, just to name a few of their functions. As you can imagine, there are thousands of different proteins and protein families described so far and obviously for some of them the function is still not clear.
Proteins are made of various numbers of amino acids that are like LEGO bricks that can be put together in a million different ways and the outcome is always different (which is why proteins are so different). There are twenty amino acids that all look slightly different and an organism requires each amino acid to make all the needed proteins and to be completely functional.
Depending on the organism, some amino acids are essential, which means the organism cannot produce the amino acid itself. So when for example a bacterium cannot make a certain amino acid, it needs to find this special amino acid somewhere in the surrounding to survive.
In this study, the researcher used the idea that a bacterium needs all of the amino acids to survive. They could show that nanotubes exist and that they are essential in certain circumstances. For this study, the researchers made two kinds of strains:
- one strain produced a lot of amino acid W and no H
- the other produced a lot of amino acid H and no W
W and H are the one letter codes for the two amino acids Tryptophane and Histidine, respectively, but these names are just confusing, so I will stick with the letters.
So, when you think about the two types of bacteria, it becomes clear that these two can easily work together so that both are happy and healthy and surviving. In theory, one strain can give its W to the other one and would get H in exchange.
The experiments then involved growing the bacteria in a medium that contained neither amino acid W or H:
- together so that they would be in close contact
- together but with a separating “wall”
- on their own
Neither of them could survive on their own as each was missing one amino acid.
When they were grown in presence of a wall none of them survived.
Interestingly, only when they were closely grown together, both bacteria survived. This meant that they needed to have direct contact with each other to survive and their survival completely depended on each other.
When they then took a closer look at the bacteria, the scientists saw that the bacteria formed some kind of tubes between themselves to exchange nutrients (Figure taken out of the paper).
It is as if you and your neighbour both want to make a cake but he misses the eggs and bought too much flour while you forgot to buy flour and got too many eggs. Neither of you would be able to make cake on your own. So you want to give your neighbour some eggs, but you cannot do that through the wall. Hence, you smash a hole into the wall to give your neighbour those eggs and receive some flour as exchange.
However, now the interesting question one might ask is how do you know that your neighbour needs eggs and how does he know that you have enough to share? You cannot just start smashing a hole in the wall just in case your neighbour needs something from you?
So how does one bacterium know that the other one is in need of a certain amino acid? They certainly will not call each other or send the other guy a message on WhatsApp…
And also, what is it that the bacteria actually exchange? Do they send the amino acid itself (hence the eggs) or do they send the DNA so that the other cell can learn how to make the amino acid itself? This would mean you send your neighbour a chicken so he can produce his own eggs… These are the interesting questions scientists keep asking and will hopefully find some answers to soon.
Take away from this week
- Bacteria can work together when the conditions require them to
- They form nanotubes to exchange cellular components