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

But have you ever asked yourself where yogurt comes from and how it is made from milk? Do you know why yogurt tastes so sour and yet delicious?

What if I told you that yogurt only tastes like this thanks to bacteria and their superpowers?

Yes, bacteria not only produce delicious chocolate, wine, beer or bread. But it is also bacteria that make yogurt from milk.

Here, we will look at which bacteria produce yogurt and what makes it so creamy, sour but also healthy.

What’s in your yogurt?

Yogurt would not exist if it wasn’t for our bacterial friends. Interestingly, it only takes two bacterial species to create this white creamy dream that we call yogurt. These two bacteria are Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.

Within milk, these two bacteria live in a symbiotic relationship. This means they help each other grow and survive. And together, they produce delicious yogurt.

These two bacteria make many molecules that give yogurt its characteristic flavor. These include lactic acid and other acids like acetoin, acetate, acetaldehyde. Because of all these acids, yogurt tastes quite sour.

Also, our two bacteria produce exopolysaccharides. Generally, bacteria use these to make biofilms. But in this case, the exopolysaccharides with their long sugar chains make the yogurt creamy and viscous.

Thanks to bacteria and the milk content, there are also a lot of healthy molecules in yogurt: proteins that are rich in energy, calcium, and vitamins B2, B6 and B12.

How is yogurt made?

It seems that all we need to make delicious yogurt are milk, our two bacterial species Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus and the right temperature. We call these two bacterial species the yogurt starter cultures.

But before their superpowers produce yogurt from milk, the milk needs to be prepared. This is basically to get rid of all the other stuff that we don’t need.

So, to kill all other microbes that might spoil our yogurt, the milk is heated to 95 °C. You might know this process as pasteurization.

After the milk cooled down to about 40 °C, our two starter bacteria are added. Next, the mix is filled into cups and sealed. The cups are then stored in a warm room – something researchers call incubation. During this incubation time, the bacteria can get to work and use their superpowers.

This means that our two bacteria start a process called microbial fermentation. They break down the milk sugar lactose and produce lactic acid and other acids.

Due to all the acids, the pH of the milk drops and it becomes sour. Now, the acids denature the milk proteins – this is the same process that you see when you heat an egg: it becomes harder and loses its fluidity. The milk becomes more viscous and gets a gel-like texture and creaminess.

Why is yogurt good for you?

We already saw that yogurt has a lot of good stuff and some studies showed that it is healthy for us because of all these molecules. But how do these vitamins, proteins and short-chain fatty acids impact our health?

For example, yogurt stimulates the immune cells that are in our guts. This improves our immune system so that it can better fight bad intruders.

Our two starter bacteria also break down some of the milk proteins and produce so-called bioactive peptides. Our guts like these peptides a lot. Hence, it transports them into our bodies where they have health benefits.

Also, the sugars in yogurt are prebiotics. This means they are the right food for other bacteria that live in our guts and that keep us healthy.

Plus, yogurt is full of protein that our bodies need to grow muscles and stay strong. Interestingly, yogurt protein has two important fractions: whey and casein protein.

The whey protein is considered a “fast protein”. This means, our body digests this type of protein faster which gives us energy immediately after eating yogurt.

The other fraction is casein or the “slow protein”. This type of protein clots in our stomach because of the acids. But our body can digest this protein clot only slowly. Hence, the casein protein gives us energy even up to 7h after eating yogurt. Like this, yogurt helps with satiety so that in general we need to eat less.

Lastly, the short-chain fatty acids in yogurt have lots of health benefits for us. They regulate the blood glucose level, insulin resistance and inhibit our appetite.

Now you have a lot of reasons to include yogurt in your daily diet plan!

What is probiotic yogurt?

Researchers found that the two starter bacteria Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus do not survive the acidity in our stomachs. Hence, they do not arrive in our guts and have no impact on our gut microbiota.

However, yogurt is a great vehicle to transport other probiotic microorganisms into our bodies. Probiotics are organisms that “when administered in adequate amounts, confer a health benefit on the host”. Also, probiotics need to be safe, well-characterized and stable while the yogurt is waiting on the shelf to be eaten.

Hence, many yogurt companies now add beneficial probiotics to yogurt. These are bacteria like Lactobacillus casei, Lactobacillus acidophilus or Bifidobacterium.

These bacteria have beneficial effects on our digestion and immune system. They help the right bacteria in our guts to grow, meaning they keep our gut microbiota healthy.

For example, in one study, researchers added a Lactobacillus casei species to yogurt and gave it to children with acute diarrhea. After a few days, these children had fewer symptoms and less abdominal pain thanks to the yogurt mix.

Is (probiotic) yogurt on your diet plan yet?

Here, we looked at two new superhero bacteria that produce the fermented creamy white dream. Even though they might not survive the passage into our bodies, they produce a lot of healthy molecules for us. Hence, they have an indirect health benefit on our bodies.

Plus, yogurt is a great vehicle to transport other probiotic bacteria into our bodies. And it seems that by eating yogurt regularly you can indeed change your gut microbiome and bring in some helpful bacteria.

So, thank bacteria for their superpowers and for providing us with this delicious food!

The post What’s in your yogurt? appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

During my last dentist sessions, I realised I barely know anything about the microbes that call my mouth their home. Those microbes and bacteria that live between my teeth and eat the same food that I eat.

Unfortunately, some of these bacteria can also cause a nasty disease that you might know as caries. And caries can lead to tooth decay and, eventually, cavities. Something, we all want to avoid.

However, as you will see below, it is not the bacteria that MAKE the holes themselves and cause caries. Rather, they fasten the process which you can prevent with good mouth hygiene.

So, let’s have a look at the microbes that live in your mouth and between your teeth and what they do there. We will then explore how some bacteria cause caries and cavities and why brushing your teeth is so important.

What your teeth are made of

Because the teeth in your mouth have to chew and shred all your food, they are made of very strong material. It’s actually the strongest material in your whole body.

This is why your body makes sure to keep your teeth healthy and strong. For example, the upper layer of your teeth – the so-called enamel – is made of pretty resilient calcium complexes. And this white and shiny layer constantly renews and mineralises on top of your enamel all the time.

Yet, at an acidic pH, the demineralisation process starts and removes calcium from your teeth. And when too much calcium leaves your teeth, the protective layer is broken. This is when holes form and thus caries and tooth decay.

So, you want to avoid getting the pH acidic in your mouth for too long. And this you can do by choosing the food you eat.

For example, acidic fruit like apples, oranges, and lemons can make the pH in your mouth acidic. Another problem can be sugary food. The microbes in your mouth can break apart the sugars in the food by microbial fermentation. From the sugars, they produce acids, which means the pH in your mouth becomes acidic.

However, your mouth doesn’t just let the pH drop easily. The saliva on top of your teeth means to buffer the pH in your mouth. Like this, it tries to keep the pH always at a constant level to prevent the demineralisation process.

About the bacteria living in your mouth

But the saliva in your mouth has another very important function. It keeps the teeth healthy and free from pathogenic bacteria. Some components of the saliva actively kill those bacteria that cause caries or prevent them from sticking to your teeth. Plus, saliva is constantly flowing through your mouth, which washes off most bacteria.

But we also have bacteria in our mouths that help us and even prevent diseases.

Some bacteria save you from caries

Some of the friendly microbes in our mouths live here and actually help us. These so-called commensal bacteria have special components – known as adhesins.

The adhesins bind to the proteins in the saliva, so that the bacteria can attach to the saliva and thus to the tooth. Here, they form a biofilm, which is a so-called plaque. This bacterial biofilm you can feel on your teeth in the morning just after waking up.

Within these biofilms, the friendly bacteria protect us from harmful pathogenic bacteria. For example, they actively kill intruding pathogens and produce toxins to keep them out of your mouth.

Plus, those commensal bacteria protect you from caries since they inhibit the demineralisation process of the enamel. For this, they produce special components that neutralise the pH and support the mineralisation process.

Other bacteria in your mouth can be nasty

And then we have pathogenic bacteria that are the sneaky ones and that can cause caries and tooth decay.

These bacteria have similar adhesins to bind to saliva and stick to your teeth. However, some of these bacteria can also bind to commensal bacteria, like the pathogen Streptococcus mutans. This one likes to stick to Candida albicans which is a member of our commensal mouth microbiota.

Other pathogenic bacteria can specifically bind to sugar molecules or use them as building blocks to increase the biofilm on your teeth. Like this, they create mixed biofilms of different bacteria.

And within this bacterial biofilm, bacterial wars are breaking out! The commensal bacteria fight the intruders to protect us. The invaders try to get rid of the friendly bacteria to make themselves a new home.

And unfortunately, pathogens have strong weapons. They can produce strong acids from sugars which make our mouths very acidic. And our friendly bacteria don’t like such an acidic environment as they have a hard time handling it. So, this acidic environment eventually kills the commensal bacteria so that the pathogens have the dental biofilm just for themselves.

Now, we call this biofilm cariogenic and this is the onset of tooth decay.

How some bacteria cause caries on your teeth

Within such a cariogenic biofilm, the pathogenic bacteria keep the pH acidic. This prevents the commensal bacteria from growing. But as we have seen above, acidity triggers the demineralisation process of the tooth enamel. And this eventually leads to holes or cavities in the tooth.

So, it is NOT the bacteria themselves that “eat” the tooth and cause caries! Caries comes from the acidic environment that these bacteria create.

Just as a bacterial biofilm protects the commensal bacteria from the surrounding, this cariogenic biofilm protects the pathogenic bacteria. They also just want to survive (but please not in our mouth!).

The cariogenic biofilm also keeps the pH acidic so that sugar molecules can better diffuse into the biofilm and the bacteria have enough food. This provides the pathogens with more sugar so that they can keep making acids. Unfortunately, the saliva and its protecting components cannot enter the biofilm.

Help your friendly bacteria protect you from caries

Basically, caries disease is a shift of our mouth microbiota from commensal bacteria to pathogenic bacteria. With more pathogenic bacteria on your tooth, the pH becomes more and more acidic around that area of the cariogenic biofilm. Hence, this triggers the demineralisation process in that area of the tooth, which can result in those nasty cavities everyone is so afraid of.

Now, that we better understand how bacteria cause caries and tooth decay, maybe it is easier to refrain from those sugary foods after hours. And if you can’t help it, make sure to brush your teeth to get rid of the sugar leftovers. This will prevent those nasty pathogens from settling down in your mouth and causing disease.

The post How bacteria cause caries on your teeth appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world