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

At the heart of this bacterium-plant relationship lies the soil bacterium Agrobacterium tumefaciens. Agrobacterium lives in the rhizosphere, the region in the soil close to plant roots. This area is full of secreted molecules from the plant as well as plenty of other soil microorganisms.

Agrobacterium tumefaciens is a versatile bacterium with two distinct lifestyles. In its free-living state, it happily lives and grows in the soil.

However, the bacterium also responds to some plant molecules, like sugars and acids, through its sensors on the surface. These molecules are often a sign of a wound within the plant root.

Once Agrobacterium tumefaciens detects such a molecule, it activates its virulence and makes it move toward the plant. The otherwise harmless bacterium is now a pathogen and can sneak into the plant where it goes on a big mission.

But just like animals, plants have defence mechanisms against bacterial pathogens as they recognise their bacterial surface. Depending on the plant’s immune system, the plant can be resistant or susceptible to the incoming intruder.

Luckily, Agrobacterium tumefaciens has the right weapons to counterattack, which is why it can infect many different plants.

Agrobacterium transfers its DNA into plants

Agrobacterium’s remarkable capability lies in its unique ability to transfer its own DNA into plant cells. For this, the bacterium has a special exporting machine sitting in its outer envelope.

Through this machinery, the bacterium sends some of its DNA. But not just any part. Agrobacterium tumefaciens has a special DNA portion in the form of a circle for this process. And on this so-called T-plasmid are only genes that help the bacterium during the plant-infection process.

When arriving in the plant cell, the T-plasmid is coated with specific bacterial proteins. These help the plasmid find its way to the nucleus of the plant cell.

Once landed in the nucleus, some of the plant’s systems are hijacked to destroy the proteins around the bacterial plasmid. This sets the plasmid free and it can now interact with the DNA of the plant cell.

Since the bacterial DNA-plasmid contains similar sequences as the plant DNA, these overlap so that the bacteria-DNA can integrate into the plant-DNA. Now, the bacteria-DNA is part of the plant-DNA and the plant activates the bacterial genes just as they were its own.

Transformed plants grow tumours as bacterial houses

Some of these activated bacterial genes cause the plant to produce certain plant hormones at very high levels. This hormonal imbalance triggers the cells to divide rapidly without control. The plant grows plant tumours, or so-called galls. You have probably seen them on the stems of plants or trees.

But Agrobacterium tumefaciens doesn’t merely cause tumours. Some of its genes – now present within the plant DNA – become factories to produce opines. Opines are an exclusive food source for the bacterium, allowing it to grow and thrive within its newly established plant-tumour home.

With Agrobacterium tumefaciens from microbiology to biotechnology

Once Agrobacterium tumefaciens’ superpower to transfer DNA into plant cells was discovered and understood, researchers used it extensively in the biotechnology field. They learned to introduce random pieces of DNA into plants, uncovering plant physiology and paving the way for genetically modified organisms.

By engineering specific DNA segments in the bacterium, researchers can transfer desirable traits and functions into plants. This technique, known as plant transformation, has enabled the development of genetically modified plants that resist pests, withstand harsh conditions or produce pharmaceutical proteins and vaccines.

A bacterium helps us unravel plant physiology

As we’ve seen so often in the microbial world, the smallest actors often have the grandest roles. Agrobacterium tumefaciens, a humble soil bacterium, is a true superhero when it comes to plant interactions.

Its ability to infect plants, exchange signals and transform its own genetic material has offered us valuable insights into the fascinating partnership between bacteria and plants. From the soil to the laboratory, Agrobacterium tumefaciens is at the forefront of illuminating the mysteries of nature and guiding us toward a deeper understanding of both the botanical and microbial worlds.

The post Learning with Agrobacterium tumefaciens: Understanding plants better 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