Photosynthesis in Bacteria

Do bacteria have photosynthesis?

Plants are great cooks! They need sunlight and water, and voilà—they produce “food” from thin air in the form of sugar. Do you know who else in nature are great cooks? Bacteria. How do these minute organisms pull off this amazing feat? Let’s head to the microbial kitchen and unravel their secrets.

Table of Contents

What is photosynthesis?

In biology, if you know some Greek, you can define many terms with just a glance. The word “photosynthesis” comes from the Greek word “photo,” which means light. The other half, “synthesis,” means “to put together.” What is being put together in the living kitchen?

 

Do you know why leaves are green? Leaves contain a pigment called chlorophyll, which has a green color. Plants use carbon dioxide from the air, and water they obtain from the soil. These react in the presence of chlorophyll and sunlight and produce sugar and oxygen. Thankfully, plants don’t use this oxygen, and instead expel it into the atmosphere for animals to breathe. In turn, plants consume the carbon dioxide that we expel and use it for photosynthesis. Photosynthesis is at the core of the survival of all life on earth.

How is photosynthesis different in bacteria?

Not all bacteria yield oxygen from photosynthesis. Purple and green photosynthetic bacteria do not yield oxygen from photosynthesis. This is known as anoxygenic photosynthesis. Instead, these bacteria produce sulfur as a by-product.

Purple bacteria are not interested in providing oxygen, they do give sulfur though
Purple bacteria are not interested in providing oxygen, they do give sulfur though, Credit: Wikimedia/kOchstudiO

Electrons are also necessary for generating ATP. ATP is a compound that provides energy, driving the process of photosynthesis forward. Plants and cyanobacteria use light energy to break water molecules into hydrogen and oxygen to yield electrons. This process of breaking water is called hydrolysis. On the other hand, purple and green bacteria use a variety of other compounds, like sulfur, to harness electrons.

 

The journey of an electron during photosynthesis
The journey of an electron during photosynthesis, Credit: Wikimedia/Govindjee, Dmitriy Shevela

Both photosynthetic bacteria and plants contain chlorophyll, but the types of chlorophyll differ in their structure. As a result, chlorophyll in purple and green photosynthetic bacteria is called bacteriochlorophyll, or BChl. Cyanobacteria are an exception, and contain chlorophyll similar to plants.

 

Sunlight contains light of seven different colors. But it also contains light rays that are not visible to the human eye. The difference between BChl and chlorophyll lies in the color of light that they work best at. Chlorophyll makes the most out of blue and red light, in the visible spectrum. BChl works best in far-red light that is not visible to the human eye.

Which part of bacteria is involved in photosynthesis?

Cells in the leaves of plants have structures called chloroplasts. Chloroplasts contain chlorophyll that plants use to absorb sunlight. Bacteria have a much simpler setup. They have small sacs on the cell membrane that store the pigments. These are called chlorosomes. In cyanobacteria, chlorophyll pigments, along with other pigments, form an organized structure called an antenna. Antennae have a large surface area. As a rule of thumb, large surface area allows better absorption, like the way a large surface area increases leaves’ exposure to sunlight. In this case, each antenna captures a lot of photons from sunlight. Photons are small bundles of light energy. These photons are needed to break water and harness electrons.

How does photosynthesis continue in bacteria?

Photosynthesis in every organism is divided into light and dark reactions. Light reaction, as the name suggests, occurs only in the presence of light. Dark reactions do not need light to proceed.

 

Purple and green bacteria use BChl to absorb sunlight in light reactions. This charges the pigment, which gives off an electron in response. This electron travels through several biochemicals, much like the baton in a relay race, and then cycles back to the bacteriochlorophyll. This process produces ATP, which the bacteria use to drive the next step: the dark reaction. In this step, carbon dioxide, or CO2, is used to produce sugar. There are various cycles and reaction paths that bacteria participate in for this process. Not all recipes are supposed to be the same, are they?

The secret to bacterial photosynthesis: bacteriochlorophyll
The secret to bacterial photosynthesis: bacteriochlorophyll, Credit: Wikimedia/Michael D. Turnbull

What is the importance of bacterial photosynthesis?

Photosynthesis in plants is crucial to life. Oftentimes, though, we forget the role of cyanobacteria. They were the first oxygenic photosynthetic organisms that arrived on earth. They changed the course of all life on earth. At the beginning, the earth was overrun with hot temperatures. The atmosphere was rich in carbon dioxide and methane, and poor in oxygen. Cyanobacteria released oxygen into the atmosphere, which displaced methane and increased the amount of oxygen in the atmosphere. Scientists refer to this event as the Great Oxygenation Event, or GOE. The GOE occurred around 2.3 billion years back. Thank cyanobacteria when you breathe in fresh air in the morning!

Cyanobacteria, the organisms responsible for complex life on earth, bloom in a lake
Cyanobacteria, the organisms responsible for complex life on earth, bloom in a lake, Credit: Wikimedia/Lamiot

Photosynthetic bacteria are solving modern problems as well. They are used in cleaning polluted waters. They are used in making biofertilizers and food for animals. Various chemicals, like lactic acid and simple sugars, are derived as by-products of bacterial photosynthesis.

A bioremediation chamber that removes pollutants with the help of bacteria
A bioremediation chamber that removes pollutants with the help of bacteria, Credit: Wikimedia/ENERGY.GOV

Now you know the secrets of these tiny kitchens. Aren’t they amazing? Humans and bacteria share a bond that will benefit us for years to come. Bacteria can help patch up the damage we have caused to nature and water bodies. These bacteria are one of human’s best friend.

Glossary

Pigment: A chemical that imparts color to an organism.

 

By-product: A substance produced in a chemical reaction that is not the main product or used by the producer.

 

Oxygenation: The process of adding oxygen to something.

 

Biofertilizer: Fertilizers produced from biological entities.

 

Hydrolysis: The chemical reaction involved in breaking water chemically into hydrogen and oxygen.

 

Anoxygenic photosynthesis: Photosynthesis in which no oxygen is produced as by-product.

Copyright @smorescience. All rights reserved. Do not copy, cite, publish, or distribute this content without permission.


Join 20,000+ parents and educators
To get the FREE science digest in your inbox!

Author

  • Anubhav Ghosh

    I am pursuing my bachelor's in microbiology from Scottish Church College, Kolkata and the lab at my college is as close as my home is to me. My interest lies in molecular biology and cell signalling, and I want to be a professor when I grow up. I believe that what we see around has a fantastic science story in it. In my free time, I love to watch soccer. Writing for Smore Science gives me the chance to explore my take on explaining the science around me in ways that everyone can grasp.