So, they talked of cocci and bacilli based on the spheres and rods that they saw under the microscope.

And they classified microbes and bacteria based on these shapes.

It came only with later, modern technologies that scientists learned that there was more to bacteria than their shapes. Even though bacteria looked similar, they had different superpowers.

Yet, some of these bacterial superpowers are indeed influenced by their cell shapes.

So, what is it about bacterial shapes? Why do bacteria look differently? And how do the different shapes of bacteria help them survive and thrive?

What gives bacteria their shapes?

To protect themselves from the environment, bacteria as well as all other organisms have cell envelopes. These keep the cellular machines and internal parts together so that a bacterium can function within this envelope.

And this envelope also gives bacteria their shape.

Both Gram-positive and Gram-negative bacteria have a layer of so-called peptidoglycan within their envelope. This peptidoglycan layer is made of sugars that are linked together by very strong bonds. This is why the peptidoglycan layer is pretty rigid and stiff and has a specific shape in each bacterium.

Either on the inside or on the outside, the peptidoglycan layer is linked to the cellular membranes. Together, these make up the bacterial envelope with a specific cell shape.

What different shapes do bacteria have?

Microbiologists have different ways to classify known bacterial shapes. Here, I will introduce you to the bacterial shapes according to what makes the most sense to me.

Rod-shaped bacteria

As the name suggests, these bacteria have a rod or cylindrical shape. Examples of rod-shaped bacteria are Escherichia coli and Bacillus subtilis.

Scientists are also convinced that rod-shaped bacteria are the evolutionary ancestors of all other bacterial shapes.

The shape comes from proteins that form long cables within the bacterial cell. These span out the whole bacterium from one end to the other.

Rod-shaped bacteria grow by two modes that we talk about in Why bacteria divide into two and grow with the help of a strong ring: First, they extend their cell size by growing the peptidoglycan, the cable proteins and the membrane.

Second, the cable proteins determine the middle of the cell, where the bacterium produces a special ring. Eventually, this ring narrows so that the bacterium divides and two bacterial cells form.

Spherical bacteria

The spherical bacteria – or so-called cocci – include many pathogenic bacteria like Staphylococcus aureus, Streptococcus pneumoniae and Neisseria gonorrhoeae.

Microbiologists think that spherical bacteria were once rod-shaped as well. However, spherical bacteria do not have these long cable proteins that extend their cell bodies. Thus, they stay spherical and grow by dividing their spherical cells right in the middle.

However, sometimes the two daughter cells do not completely divide and they stay attached to each other. This is why some spherical bacteria live as so-called diplococci.

Curved bacteria

Curved bacteria have the shape of a comma or banana and are sometimes also slightly twisted. Examples of curved or banana-shaped bacteria are Caulobacter crescentus and Vibrio cholerae.

These curved bacteria usually live in watery environments where there are flows. Here, the curved shape helps the bacteria to align with the flow while staying attached to a surface.

In the case of Caulobacter crescentus, one end of the bacterium is glued to a surface with a strong super glue. When this bacterium divides in the middle, one daughter cell remains attached to the surface, while the other one can swim away and find a new location to settle down.

Spiral bacteria

Spiral bacteria are a mix of rods and curves which give them a helical twist. Hence, these bacteria have a corkscrew shape.

Many pathogenic bacteria use their corkscrew shape to swim through gel-like solutions. This includes Helicobacter pylori and Campylobacter jejuni.

Since spiral – or helical – bacteria are also thinner, they can reach locations that are too narrow for other bacteria to reach. They also use their flagella to push themselves forward and “wriggle” through narrow pores.

Star-shaped bacteria

Some bacteria look even fancier than others: They are real stars – yes, bacteria with a star shape.

While we don’t know much yet about star-shaped bacteria, they belong to the so-called Stella species or are Methylomirabilis oxyfera. These usually grow in freshwater, soil and sewage.

The star shape comes from six little arms that extend out of the bacterial cell. These push and grow to the outside giving these bacteria a shiny star shape.

Why do bacteria have different shapes?

Now that we have seen the different shapes of bacteria, you might ask yourself, why do bacteria have these different shapes? How do they help them?

As always in biology, it comes down to how a property helps a bacterium survive in a certain location. Often, the cell shape gives a bacterium advantages over other bacteria and it is easier for them to settle down and face harsh environments.

For example, spherical cells have the lowest surface-to-volume ratio. This means they have a large envelope surface through which they can take up a lot of nutrients. All this while their cell volume is relatively small. So they don’t actually need that many nutrients. This helps cocci to grow in locations where there are little amounts of nutrients.

On the other hand, rod-shaped bacteria often have flagella. And thanks to their shapes, they are efficient swimmers. This allows them to swim to new places in cases of danger or the lack of nutrients.

Bacterial cell shapes help face harsh environments

Also, straight rod cells can pack into biofilms more efficiently and build organised structures. This helps them colonise different locations and resist dangerous environments.

Many rod-shaped bacteria also form longer filamentous organisms. These stronger and larger structures protect bacteria from being eaten by other organisms. Another advantage of these multicellular organisms is that they allow more cells to attach to surfaces and colonise hosts.

Lastly, both curved and helical bacteria use their shapes to get better around their environments. Curved bacteria grow in watery environments but also in our guts. Here, their shapes help them align with the flow of water or our gut content while they stay attached to a surface or the gut wall. This keeps them at their preferred location and protects them from being flushed away.

Spiral bacteria use a fascinating helical movement to screw through gel-like or viscous fluids. This for example helps pathogens swim through the mucus of our stomach and guts and colonise us and make us sick.

Bacteria and their shapes

Here, we looked at the different shapes that bacteria have and how these help them survive. Bacteria always face harsh and new environments and conditions and only survive if they have the right tools or means.

So, by adapting their shapes, bacteria often have advantages over other bacteria. Plus, they look cool and fabulous!

The post Looking fabulous: Why bacteria need to stay in shape too appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Also, bacteria want to grow and flourish and reproduce. But they are only single cells so that their way of reproduction is unique. They reproduce asexually meaning you only need one parent bacterium to make two daughter bacteria.

When you think about it, bacterial cell division seems very easy: Start with one bacterium, divide it in the middle and you end up with two.

However, the mechanism of cell division is pretty complex and involves at least three tasks:

• the bacterium needs to decide WHERE to divide
• get all the needed machinery to the division site
• produce new cell envelope material to separate the two new daughter cells

How a bacterium starts cell division

As you can imagine, for most bacteria it makes the most sense to divide straight in the middle. Like this, they end up with two daughter cells of the same size.

This means a bacterium needs to find its middle and mark it. While it is not completely clear yet to researchers how bacteria find the exact middle, they know it involves a so-called Z-protein.

This Z-protein can bind two things: itself and the inside of the bacterial cell envelope. But it only binds the cell envelope where it is straight and not bent. And this is only the case in the middle of the bacterial cell envelope.

Hence, the Z-proteins bind themselves in a long chain linked to the straight cell envelope. Eventually, they form a ring on the inside of a bacterial cell. And this so-called Z-ring stays in the middle of the bacterium.

Also, the Z-ring is only stable when bacteria have enough nutrients and do not encounter any stress situations. This reassures that bacteria only divide when they have all the needed supplies.

How bacteria divide and produce two daughter cells

Once this Z-ring is stable, it recruits helper machineries to this now defined division site.

The Z-ring is a sign of an upcoming cell division. Now, the bacterium knows it needs to activate machineries to produce more cell envelope material and become longer. And to increase their cell envelopes, bacteria use ferries, tunnels and bridges to transport lipids into the cell envelope.

Like this, the bacterium becomes longer and can start the actual cell division. At the same time, the Z-ring becomes tighter and the cell envelope gets its natural bend again.

Now, two processes happen at the same time: Bacteria cut open their peptidoglycan envelope to separate the two daughter cells and also produce envelope material to close both cells.

After this happened, we have two daughter cells coming from the same parent. They both share the same cell envelope and genome. This is why we consider them identical twins.

But do all bacteria produce identical twins upon cell division?

Do bacteria always divide in the middle and produce identical daughter cells?

Yes, most bacteria are symmetrical. And when they divide right in the middle, they produce two identical daughter cells.

Researchers could even watch bacteria during this process thanks to amazing microscopy techniques. You can see the single stages of bacterial cell division and how bacteria produce the cell envelope in the image below.

Yet, the bacterium Caulobacter crescentus has two different cell ends. It can stick to a surface with its sticky stalk on one end and have flagella on the other.

This bacterium also starts cell division in the middle like what we discussed above. However, the new daughter cells are now different: one is still glued to the surface and the other one has flagella and can swim away.

Also, the bacterium Helicobacter pylori with its helical shape can never really find its perfect middle. Hence, the Z-ring forms somewhere inside the bacterium and its daughter cells always have different sizes.

And then there are funny bacteria that decided they don’t even need to divide in the middle. Bacteria like Gemmatimonas aurantiaca grow “budding” daughter cells out of their own parent cells. However, researchers don’t understand yet why this bacterium chooses to divide in this asymmetric way.

Another way of asymmetric cell division happens in the bacterium Bacillus subtilis when it produces spores. During the sporulation process, the spore daughter cell grows within the mother cell. In the end, the mother cell bursts to release the spore into the environment. In this case, only one daughter cell comes out of the division process.

Why and how we want to prevent bacteria from dividing

Since cell division is an essential mechanism for bacteria, nature also found ways to inhibit it. Many antibiotics or toxins inhibit the production of cell envelope material or of the Z-ring. Like this, bacteria cannot divide anymore; they cannot grow and die.

However, we also know that some bacteria can find ways around the toxicities of antibiotics or toxins and become resistant to them. Hence, by better understanding how the whole mechanism works, researchers can hopefully find new ways to interfere with bacterial growth and find new weapons in the fight against antimicrobial resistance.

The post Why bacteria divide into two and grow with the help of a strong ring appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Many of our organs have a slimy mucus which is supposed to stop bacteria from entering the human body. But some bacteria developed mechanisms to swim through this gel-like mucus faster than others.

And these bacteria are usually the ones that make us super sick.

Meet the bacterial race swimmer Campylobacter jejuni

The pathogenic bacterium Campylobacter jejuni for example causes food-poisoning and watery diarrhoea. And this pathogen can swim through gel-like slimes, like the mucus in our bodies. Other bacteria are slowed down by this slime, but not Campylobacter jejuni. It even swims faster when it hits slime!

Why is that?

Well, that is exactly what researchers were trying to find out.

Two flagella for one movement

Campylobacter jejuni looks pretty cool. It has a helical shape and one flagellum on each side of the cell. Flagella are like fine hair that grow out of the bacterium. 

Closer to the membrane of the bacterium, the flagellum becomes a so-called hook. This hook is connected to a little motor inside the bacterium. And this motor rotates, which then rotates the hook and thus the flagellum. Now, the flagellum works as helical propeller and this movement pushes the bacterium forward so that it swims.

Since Campylobacteria jejuni has two flagella of different length, researchers were curious about how this bacterium would move. Two motors would constantly push the bacterium in the opposite direction. Plus, they saw previously that this bacterium can swim faster than other bacteria in slime. But they had no idea how these two flagella would work together. 

Wrapped in flagella

To see the flagella under the microscope, they changed them slightly. Like this, they could stain the flagella and see them as yellow fluorescent tails under the microscope.

They saw that in watery liquids, half of the bacteria had both their flagella spread to both sides and they were swimming slowly. This you can see on the left side in this video. The other half had one flagellum rotating as a tail at the back and the other flagellum was wrapped around the bacterial cell.

In gels (in the video on the right) almost all the bacteria (>95%) had one of their flagella wrapped around their cells. Plus, these cells swam faster and more directed. Mind-blowing!

Two motors are better than one

So, the researchers wanted to know why Campylobacter jejuni wraps the flagellum at the front around its cell and how that helps the bacterium to swim faster. They created two mutants of this bacterium: One bacterium did not have a front-flagellum and the other did not have a tail-flagellum. 

And they looked at how these mutants swam in comparison to the bacterium that has two flagella. In the video below, you can see the bacterium with two flagella on the left, the bacterium with the tail-flagellum in the middle and the bacterium with the front-flagellum on the right.

And as you can see, the bacteria in the middle had their tail-flagellum propelling. This pushes the bacterium forward so that it swims. Bacteria with the front-flagellum still swam. And the researchers confirmed that this front-flagellum is still rotating. It works as if it drills the bacterium forward.

So, when bacteria have two flagella, it has double the power; and the pushing and drilling together makes this bacterium super fast.

Changing direction

Next, the group was interested to see how Campylobacter jejuni changes its swimming direction. Luckily, they managed to film one bacteria at the moment when it decided to swim towards the other side.

In this video, you can see that first the front-flagellum changes the direction of its rotation. Like this, it is getting unwrapped from the bacterium.

Then, the tail-flagellum also changes its direction of rotation and the bacterium halts its movement. This looks as if the bacterium tumbles trying to get to the new direction.

Next, the former tail-flagellum wraps around the bacterium and becomes the front-flagellum.

And the former front-flagellum becomes the tail-flagellum and rotates to push the bacterium towards the opposite direction.

Two flagella to get to the perfect location

Researchers already knew that other bacteria also wrap their flagella around their cells. But often this happens in trapped places so that the bacterium tries to protect its flagellum. However, Campylobacter jejuni with its two flagella developed some efficient mechanisms to infect the human body. 

• Its helical shape helps the bacterium to drill through slimy mucus

• A rotating front-flagellum pulls the bacterium actively forward helping with the drilling movement of the bacterium

• The tail-flagellum rotates to propel the bacterium forward

• By quickly changing its swimming direction, Campylobacter jejuni can escape from confined spaces or maybe even immune cells in the human body

I’m always amazed by what bacteria come up with to escape dangerous situations…

So, now that we better understand how this pathogen moves in our bodies, we better understand how it infects us. This knowledge will now help to fight this pathogen. Let’s hope that it will help us get rid of such nasty food-poisoning-causing bacteria. 

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