Cyanobacteria or Blue Green Algae

Blue-green algae, scientifically known as cyanobacteria, are a fascinating group of photosynthetic microorganisms. Despite being called "algae," they are actually bacteria capable of producing oxygen through photosynthesis. Their vivid coloration comes from specialized pigments that interact with chlorophyll, giving rise to a range of striking hues.

What Gives Cyanobacteria Their Color?

Cyanobacteria owe their signature colors to a mix of pigments:

• Phycocyanin – A blue pigment
• Phycoerythrin – A red pigment
• Chlorophyll a – The primary green pigment for photosynthesis

These pigments combine in different ways across species, resulting in colors ranging from blue-green to red, purple, brown, or even black. Common cyanobacteria include Spirulina, Anabaena, Rivularia, Oscillatoria, and Nostoc.

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b

c

                                Blue-green algae (a) Glocapsa (b) Anabaena (c) Oscillatoria

Spotlight on Nostoc: The Jelly-Like Cyanobacterium

One of the most well-known cyanobacteria is Nostoc—a freshwater organism found in a variety of moist environments. You might have seen it before without realizing: it forms visible, jelly-like colonies that float on the surface of ponds, ditches, or water-logged soil. These colonies are surrounded by a thick mucilaginous sheath, making them easy to spot.

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How Nostoc Reproduces

Nostoc relies solely on asexual reproduction, using three main strategies:

1. Hormogonia

Short, motile filaments called hormogonia break off from the main filament. These fragments grow independently into new colonies, allowing Nostoc to spread quickly.

2. Akinetes

These are thick-walled, dormant cells that help Nostoc survive extreme conditions. When the environment becomes favorable again, akinetes germinate and give rise to new filaments.

3. Spores

While less common, certain spores may also form under stress, aiding in survival and propagation.

Note: Nostoc does not reproduce sexually.

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Anatomy: A Look Inside Nostoc

Despite its complexity, Nostoc is a prokaryote, meaning it lacks a defined nucleus and membrane-bound organelles. Here’s how its internal structure supports its survival and function:

• DNA: A single circular DNA strand floats freely in the cytoplasm.
• Ribosomes: Protein synthesis occurs via ribosomes dispersed throughout the cell.
• Photosynthesis: Nostoc performs photosynthesis using a system of internal membranes.
• Pigments: Chlorophyll a, phycocyanin, and other phycobilins help it capture light energy efficiently.
• Carbon Fixation: Carbon dioxide is absorbed and processed through the Calvin cycle to produce food.

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Where Can You Find Nostoc?

Nostoc thrives in moist and aquatic habitats, including:

• Freshwater ponds and pools
• Ditches and wetlands
• Damp soils and mudflats

It forms tangled filaments enclosed in a gelatinous matrix. These filaments can appear unicellular, colonial, or filamentous depending on the conditions.

Heterocysts: A Key Adaptation

Within the filaments, you might find heterocysts—specialized, transparent cells responsible for nitrogen fixation. These cells may appear at the ends or between other cells in the filament.

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Versatile Lifestyle

Nostoc shows remarkable ecological flexibility. It can live:

• Independently in water or soil
• In symbiotic relationships, such as inside plant tissues
• As an epiphyte, growing on surfaces of other plants

This adaptability helps Nostoc colonize diverse environments and contribute to ecosystem health by enriching soil with nitrogen.

Nostoc a blue-green alga 

Key Takeaways About Nostoc – The Blue-Green Marvel

• ✅ Nostoc is a cyanobacterium, not a true alga, but it carries out oxygenic photosynthesis.
• ✅ It reproduces asexually through hormogonia, akinetes, and spores.
• ✅ Photosynthesis is powered by chlorophyll a and accessory pigments like phycocyanin.
• ✅ Heterocysts enable Nostoc to fix atmospheric nitrogen—a vital trait for soil fertility.
• ✅ It is commonly found in wet, freshwater environments and can be seen as jelly-like colonies.
• ✅ Nostoc’s versatility allows it to exist independently, in colonies, or in symbiotic relationships.

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Did You Know?
Nostoc has been used traditionally in some cultures as a food source and is being explored today for its potential in biotechnology, including bio fertilizers and sustainable protein production.

Let the next time you spot a jelly-like blob in a pond spark curiosity—you might just be looking at one of nature’s quietest yet most important environmental engineers.