Photosynthetic Bacteria And Chemosynthetic Bacteria – Definition And Examples

Playing a vital part in the food chain, photosynthetic and chemosynthetic bacteria are essential to life on earth as we know it.

Photosynthetic Bacteria And Chemosynthetic Bacteria - Definition And Examples

You probably know that plants play a vital role in trapping CO2 within them, and introducing chemical energy to the planet through their ability to turn the light from the sun into chemical energy that humans and animals can then eat and absorb. 

But it’s not just plants that are able to utilize this function of energy conversion. Bacteria are also able to photosynthesize and can do so under incredibly harsh conditions as well.

Having been present as the very first kind of ‘life’ on earth, we owe our existence to bacteria and its innate ability to seemingly make something out of nothing. 

Using the process of photosynthesis, photosynthetic organisms produce oxygen which is an essential part of Earth’s atmosphere. 

Chemosynthetic bacteria also play an important role in shaping our Earth’s landscape and breaking down inorganic materials. 

But what is the difference between photosynthetic bacteria and chemosynthetic bacteria? Do they do the same thing? How can we tell them apart?

Read on to find out more about these definitions, examples of them in our everyday lives, and why they are so essential to life on Earth. 

What Is Photosynthetic Bacteria?

In simple terms, photosynthetic bacteria are a type of single-celled organism that can convert light energy transferred down from our sun into chemical energy that they then use to grow and reproduce. This process of energy transfer is known as photosynthesis.

What’s more, this type of bacteria is also capable of converting energy derived from inorganic substances around them. This ability means that they are also classed as a photoautotroph.

Because of this ability, they can reproduce and grow without being fully reliant on other organic lifeforms and materials to make energy. 

You can find many different types of photosynthetic bacteria throughout both the water and land environments.

They can be found throughout soils, in oceans or lakes, in sludge, paddy fields, or similar environments. We will go into the different types of photosynthetic bacteria in further detail in this article. 

These water and animal-rich environments such as the ocean have the richest density of photosynthetic bacteria. They play a key part in the food chain as they utilize the sunlight and expel oxygen which is then used in the ocean to sustain life.

Photosynthetic bacteria are literally ‘self-feeders’ which means they can survive purely off of the converted energy from light, which means as long as there is some form of light present, they can survive and thrive. 

The reason photosynthetic bacteria are so crucial to our current planet is that over 3 billion years ago, these bacteria began to slowly excrete oxygen as a by-product of converting light energy into chemical energy, and thus our then oxygen-poor atmosphere became rich with it.

This is thought to be a great turning point in the evolution of life on earth, as the oxygen forward atmosphere changed how bacteria and other living things were able to grow and adapt. 

Photosynthetic bacteria also recreate a critical function in not only the production of oxygen but also the process of carbon fixation. 

Different Types Of Photosynthetic Bacteria

As mentioned earlier in the article, there are a few different types of bacteria that can use the process of photosynthesis to sustain themselves. 

In basic terms, there are four main categories that these bacteria fall into, though there are also other groups of bacteria that are capable of photosynthetic qualities. They include:


This type of photosynthetic bacteria is also commonly called “blue-green algae”. You can most commonly find cyanobacteria in waterways and aquatic ecosystems across the globe. 

With over 2000 different identified variations of the species in the world, there are still estimated to be over 4000 that have yet to be fully identified and cataloged throughout the world due to their propensity and slight variation in different climates and regions. 

It is also a “gram-negative bacteria”. That means that its cell wall is made up of a particular substance known as peptidoglycan, which reacts to the so-called Gram Stain test. 

Cyanobacteria can cause severe infections of the blood, urinary tract, and other parts of the body as this cellular layer is usually impervious to antibiotics and can be incredibly aggressive in a healthcare environment to open cuts and wounds. 

As some species of cyanobacteria can fix nitrogen, they are often found in symbiosis with other plants and lichen that need nitrogen-rich soil to thrive, though many species of cyanobacteria live unencumbered in the water and in soils. 

Cyanobacteria And Photosynthesis

As with other algae and plant life, cyanobacteria releases oxygen as it photosynthesizes. This kind of photosynthesis is also called oxygenic photosynthesis, making cyanobacteria an oxygenic phototroph (an organism that can survive on light alone and expels oxygen). 

Though the reason they are also known as blue-green algae is that they can exhibit different shades and colors of pigmentation other than the traditional chlorophyll green we see in oxygenic phototrophs. 

In cyanobacteria, a protein called phycocyanin which is light-harvesting and pigment-binding (giving the blue-green color) is thought to have anti-inflammatory and anti-cancer properties when isolated from the algae. 

There are five types of cyanobacteria that have been found to be toxin-producers, of which there are three main types: neurotoxin, endotoxin, and hepatotoxins.

Drinking water that contains any of these kinds of toxins can make you seriously ill, usually in the form of gastroenteritis. 

As cyanobacteria do not require a source of carbon to survive, they can be found in any water environment and require filtration to prevent them from blooming in water supplies. 

As with other oxygenic phototrophs, Cyanobacteria requires the linear transfer of electrons to photosynthesize. 

These electrons are taken from the water to an essential electron donor known as NADP (Nicotinamide adenine dinucleotide phosphate) through two photosystems (PSI and PSII) that bind the chlorophyll molecules to sense different spectrums of light, which then expels oxygen and ATP (Adenosine 5′-triphosphate, the energy molecule found in all lifeforms). 

Generally, the process of photosynthesis for Cyanobacteria goes like this:

  1. Light energy from the sun is absorbed by the photosystem PSII which is located on the surface of the Cyanobacteria. The object of this is to split the water molecules, in a process called photolysis, into protons, electrons, and oxygen. 
  2. Those freed electrons are then transported by an electron transport chain molecule called plastoquinone, or PQ, into the thylakoid membrane and connected to the cytochrome b6f complex (an enzyme that catalyzes the transfer of electrons). 
  3. Using this b6f complex, these electrons are then transferred to the PSI in the cell by PC (a protein called plastocyanin). 
  4. As PSI absorbs longer wavelengths of light than PSII does on the surface of the Cyanobacteria, it excites these electrons and then reduces NADP+ (an electron created during anabolic reactions). 
  5. During this function, protons penetrate the thylakoid lumen where they encourage the synthesis of ATP(Adenosine 5′-triphosphate). Whilst this is occurring, the electrons that have come through the PSI phase reenter the plastoquinone (PQ) pool which stimulates the production of more ATP. 

 Here are some different types of Cyanobacteria:

  • Aphanizomenon
  • Aulosira
  • Chroococcus
  • Gloeocapsa
  • Gloeotrichia
  • Nostoc
  • Oscillatoria
  • Scytonema
  • Stigonema


Another type of photosynthetic bacteria is known as Proteobacteria. It is like Cyanobacteria in many ways, as it is also a Gram-negative bacteria that can be found throughout the world in waterways. 

The main difference between Cyanobacteria and Proteobacteria is that it contains many different types of seriously harmful pathogens such as Salmonella, Vibrio, and E.Coli to name a few. 

There are over 465 different types of Proteobacteria that fall into five different categories. 

Proteobacteria And Photosynthesis

Proteobacteria And Photosynthesis

The difference between Cyanobacteria and Proteobacteria is how they synthesize.

Cyanobacteria, as previously explained, are all oxygenic photosynthetic bacteria (as in, they split the water molecule and as a result release oxygen) whereas Proteobacteria, for the most part, are anoxygenic photosynthesizers. Though there have also been aerobic varieties found. 

In comparison to plant life and cyanobacteria, among others, Proteobacteria that are able to photosynthesize only have one PS (photosystem) to absorb frequencies of light rather than two. 

Because of this, they are not able to split the water molecule and release oxygen as a by-product.  

In anaerobic conditions (where there are little to no free oxygen molecules), simple organic acids are used in place of water as electron donors.

These captured electrons are taken through membrane-bound electron carriers and stored in a proton gradient( simply an area where ‘loose electrons’ can be stored before they are moved and built up until they can be used) which is finally used to produce ATP. 


Also known as the phylum Chlorobim and often referred to as green sulfur bacteria, Chlorobi is an anaerobic bacteria that only grows in anoxic conditions.

That means that it only thrives in places where there is little to no oxygen present. It also contains an essential anaerobic bacteria. 

Because of its acute need to be in anoxic environments, many of these types of bacteria can be found in habitats that are filled with sulfur-rich areas and have low-lit conditions. 

One of the other most common areas that fit into these conditions is the lower top layer of the ocean, in the area known as the photic zone.

This area of the ocean is the layer or zone that is near the ocean surface, but not close enough to come into contact with the atmosphere’s oxygen levels. 

Green sulfur bacteria thrive in this lower region of the photic zone because they can still use the sunlight as a source of energy for photosynthesis, but they do not risk coming into contact with the oxygenated atmosphere to which they are highly susceptible.

Although some other types of photosynthetic bacteria are able to get energy from other sources around them, green sulfur bacteria are known as obligate phototrophs.

That means that they have to rely on the light energy provided by the sun to harness the energy and sustain life.  

Because they rely so heavily on the energy provided by the sunlight, and they are often found in areas that do not have the brightest light (due to their inability to be in heavily oxygenated areas), they have to harvest the energy more efficiently than other photosynthetic bacteria. 

This efficient system is their photosynthetic antenna complex, otherwise known as chlorosome. 

These light-harvesting organelles inside the bacteria allow this bacteria to flourish even as low down as 2000 feet if near sulfurous gasses outputs in the ocean.

They have also been known to thrive in the murky waters of Yellowstone in the alkaline basins as they are so good at capturing and using what little light gets through the surface.  

These large and webbed complex structures can hold 200 000 bacteriochlorophyll molecules, allowing for the capture of any light photons in order to photosynthesize. 

Chlorobi And Photosynthesis

Like before, green sulfur bacteria is unlike other photosynthetic bacteria that are previously mentioned. They are anoxygenic phototrophs that need anoxic circumstances in order to carry out photosynthesis.

Unlike other phototrophs, they don’t use water and can’t split it for its electrons as they are highly susceptible to the oxygen molecules that would be released in the process.

Instead, they use an electron donor from sulfur or other sulfuric substance or compound such as thiosulfate.

These electrons from the sulfur-based compounds are used to fix carbons through the production of NADPH. 

In a notably different noncyclic route from the previous bacterium, electrons are then transported through the chain and by reducing the NADP, can then be used for carbon fixation.

Here are a few examples of Chlorobi Bacteria:

  • Chlorobium tepidum
  • Chlorobium ferrooxidans
  • Chlorobium limicola
  • Chlorobium chlorochromatii


Our last type of photosynthetic bacteria, Chloroflexi is also known as Chlorobacteria has many similarities to Chlorobi and is also known as a green sulfur bacteria

It is a variety of bacteria that has many different characteristics. They can be incredibly diverse and survive in a huge range of ecosystems as their class includes many different types of ways to absorb energy. 

For example, there are some species that exist as aerobic thermophiles, meaning they require oxygen in order to produce fuel for themselves, whereas others in the genus are anoxygenic photoautotrophs which can photosynthesize their energy from the sun.

Members of this phylum are ecologically and physiologically diverse and can be found in different habitats including sediments and hot springs etc. 

Chemosynthetic Bacteria 

Chemosynthetic bacteria are usually found in areas that do not have readily accessible light sources or oxygen and need to use a different chemical compound in order to create fuel to survive.

This kind of bacteria relies on energy provided by organic or inorganic molecules such as hydrogen sulfide, or methanol in order to synthesize organic compounds.

This method is essential for bacteria that live in incredibly harsh environments such as sea vents or sulfurous pools near volcanic sites. 

Here are a few examples of chemosynthetic bacteria:

  • Venenivibrio stagnispumantis.
  • Sulpher Bacteria
  • Nitrobacter
  • Beggiatoa.
  • T. Neapolitanus.
  • T. Novellus.
  • Ferrobacillus Ferrooxidans

Three things are needed for successful chemosynthesis. These are a carbon source (such as carbon dioxide), an electron donor, and an energy source. 

The chemosynthetic bacteria that thrive inside of tube worms living in deep hydrothermal vents at the bottom of the ocean use hydrogen sulfide as a fuel source.

They do this by converting the available carbon dioxide into a simple sugar that can be used as energy. 

The by-products of this chemosynthetic exchange depend on what carbon compound was used as a source of energy and can include water or sulfur. 

In these anaerobic conditions in the deep sea, sulfides and methane are often molecules that are used as electron donors.  

What Are The Similarities Between Photosynthetic Bacteria And Chemosynthetic Bacteria?

Both Can Produce Their Sustenance

Photosynthetic bacteria and chemosynthetic bacteria are both fully able to produce their own nutrition using elements like water, carbon dioxide, and an energy source. 

These types of bacteria that are capable of living off the elements around them and an energy source are known as primary producers. Primary producers are able to use nonliving things in order to survive and thrive.

Us humans and other animals are heterotrophs as we require the energy of another living thing, be that plant or animal, to absorb nutrition.

Because of this, they are absolutely essential to all living things as they are the primary producers and are the only organisms that are capable of living off inorganic matter or sunlight to survive, thus feeding the rest of the planet. 

Unicellular Organisms

Most bacteria are single-celled organisms. Unlike their plant brethren, they do not require a more complex system to convert light energy or inorganic compounds into fuel to survive.  

They Need Three Things To Synthesize An Organic Compound

There are three main essential parts needed in order for both photosynthetic bacteria and chemosynthetic bacteria for them to synthesize an organic compound. They need an energy source, an electron donor, and a carbon-based molecule, namely CO2. 

What Are The Differences Between Photosynthetic and Chemosynthetic Bacteria?

Whilst these bacteria have many similarities as stated above, the differences are palpable and play a huge role in their functions. 

Different Energy Source 

The most important difference to make between the two is that they use a different energy source in order to perform carbon fixing. 

Photosynthetic bacteria use energy from the sun to begin the process of photosynthesis, whereas chemosynthetic bacteria get their energy from inorganic compounds and use the energy that is stored in these material’s chemical bonds as it breaks them down. 

We can easily distinguish between the two, as the photosynthetic bacteria that use light energy are called phototrophs, and the chemosynthetic bacteria, with a few exceptions, are called chemotrophs. 


Because of photosynthetic bacteria’s need to utilize energy from the sun, they have specialized configurations called chloroplasts that contain chlorophyll to achieve this aim. These chloroplasts are a type of plastid. 

Chemosynthetic bacteria have no need to convert light energy and therefore do not contain these chloroplasts. 

Different Byproducts 

As many types of photosynthetic bacteria have to split the water molecule during photosynthesis in order to use its electrons, oxygen is one of the main gases released from the process. 

However, chemosynthetic bacteria do not have to split the water molecule to get electrons and therefore most chemosynthetic bacteria do not produce oxygen through their synthesis.  

Final Notes

Photosynthetic bacteria and chemosynthetic bacteria are part of the backbone of our oxygen-thriving planet, without which we would not be able to breathe on planet Earth.

Through this article, you should now have a better understanding of the role both of these types of bacteria play in our daily lives and the differences and similarities between the two. 

Jennifer Dawkins

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