Those bacteria that call your gut their home are the so-called commensal bacteria. Luckily, they have a special superpower: They can protect us from bacteria that cause infections and make us sick. For this, our commensal gut bacteria developed some extraordinary strategies to defend these pathogens.

So, by nurturing our friendly gut bacteria, you are also strengthening your protection against diseases. Here, we will look at what kind of bacterial wars are going on in your gut and how your gut bacteria defend pathogens and keep you healthy.

Your gut bacteria defend pathogens with toxic molecules

Bacteria have many different means to kill other microbes, competitors or even their own siblings. Often, these bacteria produce molecules that are toxic to their prey, which means they inhibit cellular proteins or machineries. Without these machineries, the prey is then lacking an essential cell function to grow or survive, so that it eventually dies.

Interestingly, gut bacteria produce and deliver many different toxic molecules of various shapes and sizes, functions and even origins.

Gut bacteria produce bacteriocins

Many bacteria produce molecules that are like antibiotics specifically to kill bacteria. These are called bacteriocins.

Some bacteriocins are simple and small molecules, while others can be big and fancy. However, they all have a similar goal: they bind to a specific target in the prey bacterium and prevent that target from working properly.

So, no wonder that many bacteria in our gut microbiome produce bacteriocins that are toxic to pathogenic intruders. Also, we carry a lot of different bacteria in our guts and they all produce different bacteriocins. Hence, incoming pathogens face this huge load of toxic molecules making it really difficult to establish themselves in our intestines.

For example, one bacterium that loves the warmth and lack of oxygen in our gut is the bacterium Ruminococcus gnavus. And this one produces at least two bacteriocins, Ruminococcin A and C, that are toxic against human gut pathogens like Clostridium perfringens.

Other friendly gut bacteria, like Escherichia coli or Blautia producta, also produce bacteriocins that are toxic to pathogens, like Enterococcus faecalis. And some of their bacteriocins can even impact our gut cells by activating and strengthening our immune response.

Gut bacteria produce short chain fatty acids from fibres

Another way to protect against pathogenic gut bacteria is directly related to your diet. When we eat a lot of fibres, which are non-digestible carbohydrates, our friendly gut bacteria break these up. From these fibres, they produce small molecules that are called short-chain fatty acids, which have many positive health benefits for our overall wellbeing.

Interestingly, when we have a lot of these short-chain fatty acids in our intestine, the pH drops. This is already pretty difficult for most pathogenic bacteria, as not many can handle this acidic environment.

Plus, short-chain fatty acids diffuse into pathogenic gut bacteria where the pH drops as well. This can disturb many cellular machineries from functioning properly and not many bacteria have the right tools to defend against this attack, so they’ll die.

Gut bacteria convert bile acids into toxic compounds

To better digest the fats in food, our liver produces bile acids. These molecules bind fatty acids and lipids so that we can take them up better into our bodies.

But some of our friendly gut bacteria can convert these primary bile acids from our liver. For example, one of these bacteria, Clostridium scindens, transforms them into secondary bile acids that can bind the lipids of bacterial membranes.

Like this, secondary bile acids open the membranes of some pathogenic gut bacteria, like Staphylococcus aureus, Bacteroides thetaiotaomicron or Clostridoides difficile. This eventually kills the intruders and keeps our guts pathogen-free.

Killing pathogens with bow and arrow

Yes, also direct bacterial wars are happening in our guts! And they are nasty!

Some bacteria use tiny little bows to shoot deadly arrows into other bacteria. And these arrows can be incredibly toxic so the shot bacterium has barely any chance to survive the attack.

Luckily, our gut bacteria use their bows and arrows to defend against gut pathogens. For example, commensal bacterium Bacteroides fragilis has three different bows and can shoot various arrows. And research showed that this bacterial friend can protect us from bacteria that otherwise cause intestinal diseases.

Interestingly, Bacteroides fragilis is not opposed to hit’n’kill its own toxic bacterial siblings since some members of his family can indeed make us sick. But our friendly Bacteroides fragilis collected many different immunity proteins against its evil siblings so that their toxic arrows cannot harm it. Instead, Bacteroides fragilis keeps shooting and killing until we are safe from the pathogenic sibling.

Keeping nutrients from pathogenic gut bacteria

Another important way how gut bacteria defend pathogens is by keeping nutrients away from them. In all mixed microbial communities, bacteria fight for nutrients, especially for metals like iron, zinc but also sulphur sources.

Luckily, our gut bacteria developed some sneaky ways to steal these metals from gut pathogenic bacteria. By sending out special proteins that bind these metals very tightly, the commensals make sure to keep these metals from the pathogens. And if the pathogenic bacteria don’t have enough of these essential metals, they won’t survive and will eventually die.

Strengthening the mucus layer to block pathogenic gut bacteria

When you think about it, your gut is not part of your body – even though it is inside of you. All the food that we eat, stays within this digestion tube (mouth, oesophagus, stomach, intestines) until it comes out on the other side.

And to protect us from harmful microbes and molecules, we need to have a clear physical barrier from the content of the tube. This barrier is the so-called epithelial layer, which is covered by a slimy mucus on the outside. And this sticky slime helps keep off intruding microbes so that they cannot breach through the epithelial wall and get into our bodies.

Luckily, our helpful gut bacteria help us maintain this slimy defence wall. As bacteria produce SCFAs close to the mucus layer, the epithelial wall produces more slime. And if the slime gets thicker, gut pathogenic bacteria have more difficulties getting into our bodies.

To help the slime grow, some bacteria adapted very well to the conditions within the gut. For example, the friendly gut bacteria Akkermansia muciniphila and Ruminococcus gnavus cut off the very end of the mucus layer and feed themselves with them. This does not harm the mucus itself, but it keeps these bacteria close by. And this in turn triggers the epithelial wall to produce more mucus. So, everyone wins.

How to help your gut bacteria defend pathogens

Now, that you better understand how your gut microbiome defends pathogenic gut bacteria, make sure you support them keeping you healthy. By feeding your gut bacteria the right foods, you will help them be comfortable and happy in your gut. And when the right bacteria grow within you, they will gratefully protect you from nasty intruders!

Another idea for researchers is to use what they have learned to keep you healthy. The idea is to develop probiotics or prebiotics that help us defend against nasty pathogens. For example, you might take pills containing toxins against pathogenic gut bacteria or probiotics with bacteria that can fight off pathogens.

Whatever it may be, you can always help your gut bacteria be happy in your intestines by eating the right things. That means lots of fibre and veggies! ?

The post How bacteria in your gut microbiome defend pathogens appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

The soil of the forest is full of nutrients, metals, water, oxygen and everything else a bacterium wants and needs.

However, within this paradise, there is not only one bacterium. There are thousands of them. Even more.

And each one of them wants to survive, thrive, grow and reproduce.

So, every single bacterium is making sure it is the major inhabitant of this small place in the soil.

And sometimes, there is no other way than to kill the other bacteria.

To get rid of these annoying food-stealing neighbours, bacteria have developed some fancy killing machines. They poke, they shoot, they burn or they fight.

One of these machines is even more special than the other ones. The so-called type VI secretion system is an incredibly efficient nanoweapon. It works like a bow and arrow. And here, we will find out why.

A bacterial nanoweapon as a crossbow

You can imagine the type IV secretion system as a tiny crossbow with a sharp arrow. It looks similar to the bow and arrow in the picture below.

We call our bacterium with the crossbow an attacker (this is the one in grey). When our attacker meets another bacterium that could be a danger (like the one in purple) we call this one prey.

So, our attacker bacterium has this crossbow that sits on the inside of the bacterial membrane. And the crossbow has a strong stem (in black) that holds an arrow.

And the arrow of the type IV secretion system is the real deal. It consists of three different but important parts. Each one of them makes sure the prey bacterium suffers immensely.

In most cases, the arrow is incredibly powerful. As soon as the attacker shoots the arrow into the prey, the prey dies and the attacker wins. 

So, let’s look at this in more detail.

A bacterial nanoweapon with special arrows

The arrow is clamped within the crossbow and has a very sharp tip and a long spike. The tip of the arrow is needed to punch a hole into the prey bacterium.

After the attacker punched a hole in the membrane of the prey bacterium, it delivers the whole arrow into the prey. The interesting thing is that toxins are glued to the arrow. So, when the attacker shoots the arrow into the prey, the glued toxins reach the prey as well. 

And these toxins are the real problem. They are toxic and even lethal to the prey bacterium. So, yes, our attacker came here to kill.

Generally, bacterial toxins mean to destroy essential parts in the prey bacteria. And this is how the attacker kills and wins!

Bacteria have many toxins

There is another cool thing about these attacking bacteria. Some of them have more than just one crossbow. Some bacteria have even up to six different ones. So much killing potential!

And all of these crossbows can shoot different arrows. Sometimes, bacteria have around ten different arrows lying around in their cells.

To make it even more mind-blowing: Each of these arrows has its own specific toxin glued to it. And some arrows carry multiple different toxins. 

This means, that a bacterium has many different toxins. But don’t forget that within a bacterial cell, there are a bunch of other proteins and cellular stuff.

So, how does a bacterium make sure that it fires a specific arrow with a specific toxin?

Well, both the toxin and the arrow have fitting patches. And bacteria use these patches to glue a toxin to a specific arrow.

Once arrows are loaded to their designated crossbows, they sit in the membrane and wait to be fired. So, when a bacterium meets a prey that it wants to kill, it can choose between its crossbows, arrows and toxins. Each one of these combinations seems to have an advantage under a special circumstance and against a specific prey.

And our attacker can just choose what is right at that time.

The type VI secretion system – a truly special bacterial nanoweapon

Currently, scientists are working hard to understand exactly how this fascinating bacterial nanoweapon works. One goal is then to use this killer machine in other applications.

For example, one aim of researchers is to have a tool to kill bacteria that we cannot fight with commercial antibiotics anymore. Another idea is that we better understand how toxins glue to the arrow so that we can create bacteria that deliver therapeutics, vaccines or other drugs.

So, let’s see what future research into this amazing bacterial nanoweapon will bring us.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world