And only thanks to pigments, life on Earth is possible. Pigments were the first molecules that microbes used to harvest sunlight. Microbes could then transform the light energy into chemical energy and produce oxygen.

Even the brown-reddish haemoglobin in your blood is an essential pigment as it transports oxygen within your body. Also for bacteria, pigments and their colours have life-saving functions. Here, we will look at how biopigments colour the bacterial world and what bacteria gain from producing them.

Bacterial pigments bring colour to the world of bacteria

Biopigments are molecules with complex chemical structures and at least one excited electron. Depending on the electron’s arrangement, a pigment absorbs light at a specific wavelength. It reflects the colour of the unabsorbed wavelength, which gives the pigment its colour.

As the function of pigments depends on the incoming light, sunlight plays a crucial role for bacteria with pigments. By adding certain pigments to their membrane, bacteria can adapt to environments that are directly affected by sunlight or the lack of it. This gives them an advantage over those bacteria that lack these pigments.

However, some bacteria also use pigments for other purposes, which we discuss further in this article.

Microbes harness photosynthetic power with colourful pigments

Sunlight is incredibly powerful since each light photon contains energy. Bacteria adapted to harvest energy from sunlight with special pigments.

Pigments can capture the incoming photon and transfer its energy to other molecules. This process transforms the incoming light energy into chemical energy. So-called phototrophic microbes are those that gain their energy from light.

The best-known example of a photosynthetic biopigment is chlorophyll in plants, algae and cyanobacteria. Cyanobacteria produce several complexes of bacteriochlorophylls to absorb blue and red light. As the green light is not absorbed, it is reflected, which is why chlorophyll – and thus cyanobacteria, algae and plants – are green.

Some bacteria harvest more light by producing several pigments of different types. They then arrange them in an optimal formation according to the incoming light.

For example, carotenoids capture energy in the green-blueish range and pass it on to the associated chlorophyll. Together, these photosynthetic complexes absorb light energy from almost the entire wavelength spectrum.

Halophilic bacteria and archaea are microbes that produce carotenoids to capture sunlight. You may have seen salt ponds with a reddish colour. This comes from the red and pink-coloured archaea Halobacteria, bacteria Salinibacter or algae Dunaliella. Thanks to their colourful carotenoids, these microbes adapt to salty waters that are exposed to direct sunlight.

Cyanobacteria in the deep sea, lagoons, lakes, ponds or rivers produce similar molecules to chlorophyll. These absorb the blue-green light in water, which allows these bacteria to survive in these dark environments. If you have ever seen a lagoon shining yellow or orange, this was probably due to the colourful cyanobacteria inside.

Bacterial biopigments protect from too much light

As light is full of energy, bacteria also need to protect themselves from getting burned. For this, they produce pigments that take up the excess light energy. Like this, the main photosynthetic complex does not get damaged.

Carotenoids and xanthomonadins are the colourful sun blockers of the microbial world. These molecules absorb high-energy light to protect chlorophyll from damage. Over 600 different carotenoids were described and they usually come in yellow-orange-reddish colours.

The yellow xanthomonadins absorb wavelengths within the energy-rich UV spectrum. Bacteria like Xanthomonas campestris live on plant leaves where they are exposed to direct sunlight. Hence, their yellow xanthomonadin coats are like self-made sunblocks protecting the bacteria.

Also, the pigment melanin shields the producing cell from energy-rich sunlight. Many bacteria living in the soil or bacterial spores produce these pigments. Here, melanin absorbs light from a wide range of the light spectrum to protect the inner of the cell. Hence, melanin-producing bacteria, like Vibrio cholerae and Streptomyces bacteria, are brown or black.

Bacterial pigments let electrons flow and save energy

Since bacterial pigments allow electrons to flow, they can also be energy conductors. Hence, some pigments are important components of energy complexes and synthesis machineries.

For example, yellow flavins are pigments involved in cellular metabolism. The main flavin is riboflavin, which you may know as vitamin B12. This essential molecule – produced only by bacteria – allows our bodies to work.

Phenazines are unique bacterial pigments with yellowish-green fluorescent colours. Pyocyanin, exclusively produced by Pseudomonas bacteria, shuttles electrons – and thus energy – during the respiration process. Hence, pyocyanin is essential for Pseudomonas as it keeps the bacteria healthy and alive.

Some biopigments have anti-oxidant effects

Bacterial pigments don’t just help adapt to external environmental conditions like the sunlight. They also guard the inner bacterial cell from stressful situations.

Excess or uncaptured energy or escaped light photons can react with oxygen. This process produces so-called oxygen radicals, which can damage molecules inside the bacterium. Known as oxidative stress, oxygen radicals can even become life-threatening for bacteria.

Carotenoids and xanthomonadins protect bacterial cells from oxidative stress. These pigments transform the free oxygen radicals into harmless molecules. Since carotenoids and their product vitamin A have similar functions in humans, it is only healthy for us to take up a lot of these with our diet.

In the bacterium Gemmatimonas aurantiaca, orange carotenoids also work like sunscreen and oxidative shield. These pigments both give the bacterium its bright orange colour and protect it from too much sunlight.

Bacteria combat microbial enemies with coloured pigments

As night falls, many bacterial pigments reveal their darker sides. They become important weapons for microbial warfare. Without sunlight, several pigments take on roles as virulence factors and antimicrobials as they mess up cells’ energy and oxygen household.

For example, prodigiosin is the red weapon of Serratia marcescens. As prodigiosin inhibits the growth of several bacterial, fungal and insecticidal pathogens, Serratia marcescens is an important biocontrol bacterium of plant disease.

You may have seen prodigiosin-producing Serratia bacteria on contaminated food. They develop these red, blood-like dots.

Violacein is a purple pigment with anti-viral, anti-bacterial and anti-cancer properties. For example, Chromobacterium violaceum sends membrane bubbles filled with violacein to kill bacterial enemies.

Similarly, Janthinobacterium lividum protects frogs and salamanders as it lives on their skins. Here, the bacterium throws violacein at pathogenic fungi that would otherwise infect and harm the animals.

Pyocyanin, the fluorescent electron-shuttling pigment in Pseudomonas, is also very sensitive to oxygen. It even turns Pseudomonas aeruginosa cultures in the lab blueish just by shaking and airing them.

Yet, not all bacteria have an appropriate coping mechanism for pyocyanin. Hence, these bacteria suffer oxidative stress when they come into contact with this pigment. This is why Pseudomonas uses pyocyanin also to fight bacterial and fungal enemies.

Vivid pigments colour the bacterial world

The Bacterial World is colourful – one of this blog’s taglines. You may have asked yourself what this is about and why bacteria have so many different colours.

From the dazzling pink of halophilic microorganisms to the sunny yellow of phytopathogens, bacterial pigments give their producers shiny and vibrant colours. But thanks to the colourful biopigments, bacteria also gain abilities to survive in new and challenging environments.

Some of these bacterial pigments are essential for us humans and even life on Earth. From some of these colourful biopigments, we produce vitamins that we need for our own metabolism. Also, every oxygen molecule that you just took up with your last breath, at some point, was transformed by a bacterial chlorophyll pigment.

So, I guess it is yet again time to be grateful to bacteria and their vibrant and life-enabling activities!

The post Creating the colours of the rainbow: Bacteria and the vibrant world of pigments 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.

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