Cyanobacteria: Overview, Structure, Diagram, Examples, Uses, Cyanobacteria

Cyanobacteria, also called blue-green algae, are a type of bacteria that can make their own food using photosynthesis, just like plants. They get their name from their blue-green colour and are believed to be one of the earliest life forms to release oxygen into Earth’s atmosphere. These tiny organisms live mostly in water and play a very important role in the environment. They form the base of many aquatic food chains, providing food for small water animals. Cyanobacteria also help in nitrogen fixation, making the water more fertile for other life forms. Cyanobacteria are a topic of the chapter Biological Classification in Biology.

This Story also Contains

1. What are Cyanobacteria?
2. General Characteristics of Cyanobacteria
3. Classification and Cyanobacteria Types
4. Reproduction in Cyanobacteria
5. Photosynthesis in Cyanobacteria
6. Habitat And Distribution
7. Ecological and Environmental Significance
8. Recommended video for Cyanobacteria

What are Cyanobacteria?

Cyanobacteria are among the first microorganisms that were ever formed on the planet Earth, with a fossil record estimated of about 3 billion years of age. 5 billion years. It is needed to recognise cyanobacteria, as they are the world’s most diverse group of bacteria that can perform oxygenic photosynthesis, and therefore, being important to the biosphere, oxygen producers can significantly define the early Earth’s atmosphere.

Traditionally, cyanobacteria are of great importance to the history of life because they played the role of the Great Oxidation Event, through which the majority of aerobic organisms appeared. These characteristics reveal their flexibility and significant function in ecological and evolutionary research, as they have numerous forms and environments.

General Characteristics of Cyanobacteria

The characteristics of cyanobacteria are defined as:

Morphological Features

Cyanobacteria present themselves in many forms; they may be isolated, colonial or filamentous. They commonly exist as surface substrata and form mats or biofilms in aqueous surroundings, demonstrating their structural diversity in various ecosystems.

Cyanobacteria structure

Pigments and Colouration

Their pigments are chlorophyll a, phycobiliproteins and carotenoids, giving cyanobacteria their typical blue-green colour. These pigments are very vital in the absorption of light energy, which is important in the photosynthesis process.

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Classification and Cyanobacteria Types

The classification and types of cyanobacteria are described below-

Classification and Types of Cyanobacteria

• Kingdom: Monera

• Phylum: Cyanobacteria

• Common Name: Blue-green algae

• Cell Type: Prokaryotic (no nucleus)

Types of Cyanobacteria Based on Structure and Habitat

1. Unicellular Cyanobacteria: Made of single cells. Example: Gloeocapsa, Chroococcus
2. Colonial Cyanobacteria: Cells live in groups or colonies held together by a gelatinous covering. Example: Microcystis
3. Filamentous Non-Heterocystous Cyanobacteria: Long thread-like chains (filaments) of cells, no heterocysts (nitrogen-fixing cells). Example: Oscillatoria, Lyngbya
4. Filamentous Heterocystous Cyanobacteria: Have special nitrogen-fixing cells called heterocysts along the filaments. Example: Anabaena, Nostoc, Aulosira
5. Branched Filamentous Cyanobacteria: Filaments show true or false branching structures. Example: Stigonema, Scytonema

Reproduction in Cyanobacteria

Reproduction in cyanobacteria is of the following types-

• Asexual Reproduction: Cyanobacteria reproduce without forming gametes (no sexual reproduction).

• Binary Fission: Most common method; one cell divides into two identical cells.

• Fragmentation: In filamentous forms, the filament breaks into pieces, and each piece grows into a new individual.

• Hormogonia Formation: Short segments of filaments (called hormogonia) break off and develop into new filaments.

• Spore Formation: Some cyanobacteria produce akinetes (thick-walled spores) to survive harsh conditions like dryness or extreme cold.

• No Sexual Reproduction: Cyanobacteria do not reproduce sexually or form zygotes.

Photosynthesis in Cyanobacteria

The photosynthetic process in Cyanobacteria is described below-

Light-Dependent Reactions

Light reactions in cyanobacteria take place at the sites of thylakoid membranes where chlorophyll will capture light energy to facilitate water molecule breakdown and liberation of oxygen, protons and electrons. This process creates ATP and NADPH required for the subsequent phases of the process of photosynthesis.

Light-Independent Reactions (Calvin Cycle)

ATP and NADPH that were formed during the light-dependent reactions are utilised in the Calvin cycle that takes place in the cytoplasm. In this cycle, carbon dioxide is converted into organic carbon and builds up glucose for energy and food for the cyanobacteria.

Habitat And Distribution

The habitat and distribution of Cyanobacteria are described below-

Aquatic Environments

Cyanobacteria are universal in their distribution from freshwater lakes, rivers and ponds to the oceans and seas. They are often found in quite dense numbers and fronds, especially in eutrophic conditions, where they are important components of the food chains and nutrient cycling.

Terrestrial Environments

In terrestrial ecosystems, cyanobacteria live in different types of soils, on rocks, or the arid deserts. They participate in nitrogen fixation and act as nitrogen sources in the soil, are frequently associated with fungi and contribute to the formation of lichens, which are extremophiles.

Ecological and Environmental Significance

The ecological and environmental significance of Cyanobacteria is listed below-

Nitrogen Fixation

Mechanism of nitrogen fixation

Among other unique structures, plants have heterocysts where they perform nitrogen fixation, hence making nitrogen available in the environment by breaking nitrogen gas (N₂) into ammonia (NH₃) through the nitrogenase enzyme.

Importance of nutrient cycling

Symbiotic Relationships

Cyanobacteria are in a mutualistic partnership with fungi, which are found in lichens; the benefactors get carbohydrates from the cyanobacteria when they perform photosynthesis, and they, in turn, get shelter and moisture. They also attach to plants such as the water fern known as Azolla, which also benefits in nitrogen fixation in rice fields.

Role In Aquatic Ecosystems

Primary producers

Primary producers include the cyanobacteria, which engage in photosynthesis, thus synthesising organic compounds and oxygen used as the base of the consumers’ trophic level in the aquatic ecosystems.

Impact on water quality (eutrophication)

Over-enrichment of the water body by nutrients causes cyanobacteria to bloom in large numbers; their presence causes eutrophication, which will deplete oxygen in the water, produce toxins and in the long run, deteriorate water quality, which will hurt aquatic life and man.

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