Difference Between Photosynthetic and Chemosynthetic Bacteria

The key difference between photosynthetic and chemosynthetic bacteria is that photosynthetic bacteria obtain energy from sunlight in order to produce carbohydrates while chemosynthetic bacteria obtain energy from the oxidation of inorganic substances in order to produce carbohydrates.

Organisms can be categorized based on their mode of nutrition. Autotrophs and heterotrophs are two such main categories. Autotrophs can produce their own food while heterotrophs depend on other organisms for foods since they cannot produce their own food. In order to produce their own food or carbohydrates, autotrophs use two main processes: photosynthesis and chemosynthesis.

Photosynthesis is powered by the energy of sun while chemosynthesis is powered by the energy derived from the oxidation of chemical compounds, mainly inorganic substances. There are photosynthetic bacteria and chemosynthetic bacteria. Photosynthetic bacteria produce food by photosynthesis while chemosynthetic bacteria produce food by the energy obtained from the chemical break down.

CONTENTS

1. Overview and Key Difference
2. What is Photosynthetic Bacteria
3. What is Chemosynthetic Bacteria
4. Similarities Between Photosynthetic and Chemosynthetic Bacteria
5. Side by Side Comparison – Photosynthetic vs Chemosynthetic Bacteria in Tabular Form
6. Summary

What are Photosynthetic Bacteria?

Photosynthetic bacteria are a group of bacteria called cyanobacteria or blue-green algae that can produce carbohydrates by photosynthesis. Therefore, they are photoautotrophs. They contain different photosynthetic pigments such as chlorophyll-a, phycobilin and phycoerythrin. Therefore, these organisms are also known as prokaryotic autotrophs. Photosynthesis takes place in plasma membranes of cyanobacteria.

Cyanobacteria are unicellular filamentous organisms. Sometimes they exist as cyanobacterial blooms as well. The size of cyanobacteria varies from 0.5 – 60 µm. They are mainly found in freshwater environments and in damp terrestrial environments. Cyanobacteria reproduce via binary fission. It is the main mechanism of cyanobacterial cell proliferation and reproduction. However, some species undergo fragmentation and multiple fission.

In addition to their photosynthetic ability, cyanobacteria can also fix atmospheric nitrogen. They contain a special structure known as heterocyst which is capable of fixing nitrogen from the atmosphere. Cyanobacterial species such as Anabaena and Nostoc are popular as nitrogen-fixing cyanobacteria.

Besides, cyanobacteria are widely used as nutritional supplements due to the nutrient-rich nature of some species (Spirulina, Cholerella). Moreover, some species serve as inoculants in the manufacturing process of biofertilizers. Cyanobacteria also act as an integral partner in many symbiotic relationships. Lichen is one such important symbiotic interaction existing between fungi and cyanobacteria. Lichens are extremely important in agriculture.

Despite having many positive impacts, cyanobacteria accumulation can lead to eutrophication in waterways, making them a significant pollutant of water bodies. Therefore, cyanobacteria also act as indicators of water pollution.

What are Chemosynthetic Bacteria?

Chemosynthetic bacteria are a group of bacteria that can produce their own food by the energy obtained from the oxidation of inorganic substances. They are also a group of autotrophs. In fact, they are chemoautotrophs. Unlike photosynthetic bacteria, they are unable to carry out photosynthesis or trap energy from sunlight. But they can produce carbohydrates from CO₂ and H₂O by the energy of chemical breakdown. Therefore, they don’t need sunlight or pigment systems. They use the energy released from the oxidation of inorganic compounds to produce carbohydrates.

Different chemosynthetic bacterial species utilize different inorganic sources. For example, chemosynthetic bacteria that are living in hydrothermal vents oxidize hydrogen sulfide to obtain energy for food production. Some other bacteria oxidize methane to produce energy while some uses nitrites or hydrogen gas to produce food. Moreover, some bacteria obtain energy from sulfur while some obtain energy from iron. Similarly, different chemosynthetic bacteria utilize different inorganic substances to obtain energy.

 What are the Similarities Between Photosynthetic and Chemosynthetic Bacteria?

• Both photosynthetic and chemosynthetic bacteria belong to Kingdom Bacteria.
• They have a prokaryotic cellular organization.
• In addition, they are autotrophs that can produce their own foods.

What is the Difference Between Photosynthetic and Chemosynthetic Bacteria?

Photosynthetic bacteria carry out photosynthesis and produce their own food, utilizing the energy from sunlight. Meanwhile, chemosynthetic bacteria carry out chemosynthesis and produce their own food, obtaining energy from the oxidation of inorganic substances. So, this is the key difference between photosynthetic and chemosynthetic bacteria.

Moreover, photosynthetic bacteria live in places where there is sunlight while chemosynthetic bacteria live in places where there is no sunlight. Also, another difference between photosynthetic and chemosynthetic bacteria is that photosynthetic bacteria have pigments to trap sunlight while chemosynthetic bacteria do not have pigments.

The below infographic summarizes the difference between photosynthetic and chemosynthetic bacteria.

Summary – Photosynthetic vs Chemosynthetic Bacteria

Photosynthetic bacteria are a group of bacteria that can produce their own food by photosynthesis. They are also called cyanobacteria. Meanwhile, chemosynthetic bacteria are a group of bacteria that carry out chemosynthesis in order to produce their own foods. In short, photosynthetic bacteria utilize energy from sunlight for carbohydrate production, while chemosynthetic bacteria obtain energy from the oxidation of inorganic substances such as sulfur, hydrogen sulfide, methane, etc. Thus, this summarizes the difference between photosynthetic and chemosynthetic bacteria.

Reference:

1. Gutierrez, Jose Juan. “What Are Chemosynthetic Bacteria?” Owlcation, Owlcation, 12 Jan. 2018, Available here.
2. “Blue-Green Algae.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 29 Dec. 2017, Available here.

Image Courtesy:

1. “Cyanobacteria guerrero negro” By NASA –  (Public Domain) via Commons Wikimedia
2. “Venenivibrio” By Thermophile~commonswiki assumed (based on copyright claims). – Own work assumed (based on copyright claims) (CC BY-SA 3.0) via Commons Wikimedia