Infecti…What now?
You may or may not have heard, but bacteria have so-called injectisomes, which I personally think sound both terrifying and very much like a sci-fi concept. But I can assure you, it is both very real and also very useful…For the bacteria that is.
Like any good story, we should start from the beginning.
Bacteria, like all other life-forms, has one goal: To survive and multiply.
They do so by living among us and inside us. It is estimated that at any time the number of living bacteria in our body at least equals the number of human cells. That means that there are as many bacteria inside us as there are cells in our body! (Source)
The good bacteria is always working away and helping us to digest our food. Our gut microbiome (that is, the bacteria in our intestines) is essential for proper digestion and healthy life. The importance of the small organisms inside us has become a hot topic over recent years and is undergoing extensive scrutiny — for a good reason. The influence of bacteria on our behavior and health is undeniable. I’m sure I’m not the only one that gets grumpy when hungry, and that’s only one way our digestion and microbiome bacteria affect our everyday life.
Unfortunately, it’s not only good bacteria that live inside us. Disease-causing bacteria like Salmonella and E. coli (yes, the poop-bacteria) cause several unpleasant side effects when they manage to infect us. They infect the gut cells by sticking to the gut lining and pumping our cells full of toxins and other unpleasant things, which in the case of E. coli causes bloody diarrhea. (Source)
I know, it sounds very pleasant so far.
Just to be clear here, not all bacteria of the same family will cause a problem for humans. Most kinds of E. coli will happily live inside us and digest whatever remains of our food — human and bacteria co-existing in perfect harmony. The harmony only gets threatened when the bad guys, like the Enterohemorrhagic E. coli, start showing up. (Source)
In order to understand how these diarrhea-causing bacteria manage to pump us full of the bad stuff, we need to look at the entry site — Our gut.
Our gut is, like our skin, a selective barrier against the outside. It absorbs all the food and nice things we ingest to enable the rest of our body to do whatever it is we want to do — Run around, drink coffee and chat to our good friends, or spend time alone in a café writing out an article about diarrhea-causing bacteria. Its main and most important functions are to keep us safe against all the things that want to get inside our system to do harm and to only let the good stuff through. Our gut is basically a big specially trained bodyguard or bouncer.
Our intestine cells manage to create a barrier against the bad stuff the same way we humans try to keep things out: by creating walls. The only difference is that where humans make walls out of stone, cells make them out of fat and other teeny tiny stuff that helps segregate things on either side of their cell-wall. It seems that building walls is not only a human concept but is actually a necessity for life! Without them, we could never keep the bad stuff and toxins out of our bodies, and that would make it difficult for life to prosper.
The aforementioned bodyguard is made out of our intestinal cells, which are specialized in taking in good stuff and rejecting bad stuff. Sometimes things go wrong, and there we go: Diarrhea or other nasty surprises, depending on exactly what got into our system.
Normally our gut cells are quite good at rejecting bad things, but some bacteria have learned to force their way through our gut-barrier by creating their own entrances and are therefore not being kept out by our gut-bouncer! Bacteria is truly sneaky and hell-bent on survival.
They create backdoors by using their injectisomes, which are basically multiple tiny needles they force through our cell-walls and into our body. When the needles have penetrated the cell wall, the bacteria can then push through all the toxins and other stuff that makes our internal environment favorable for them to live in. That is what bacteria and life, in general, are always trying to do: to make the environment suit themselves. In that regard we humans aren’t that different from bacteria, we too alter our environment to suit our needs.
When the bacteria has changed our cells enough, they’ll start the colonization. In the case of E. coli, they’ll start to grow inside our intestines and attach to the surface barrier. Other bacteria, like some kinds of Salmonella, will literally force their way into our cells when they’ve made them hospitable and start multiplying inside them. You heard that right, the bacteria will live inside the very building blocks that make up our entire body!
The injectisome system starts developing when the bacteria cells come into contact with the host cells, there the bacteria will start by producing these needle-like apparatuses and later produce the stuff they want to send through them. Stuff that in the end will enable them to live and prosper inside us.
The study of this system has for a long time been focused on shutting it down and therefore making infection if not impossible, then harder, which is reasonable since not many people want to have harmful bacteria living inside them nor deal with the consequences of this!
We, The iGEM team of the University of Copenhagen 2018, are going to take another angle on this problem. We want to highjack the injectisome system and make it work for us instead! We want to turn what is diarrhea-causing — but highly ingenious — bacteria into our own biological protein-producing machines. These proteins could, in the end, be used for everything from medicine to food!
We’re still in the early days of lab-work design, but I’m personally very excited!
For those of you that are used to hardcore scientific reading, I recommend this review.
