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Caption: Cyanobacteria
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Cyanobacteria, also known as blue-green algae, are ancient unicellular photosynthetic organisms. Cyanobacteria are one of the oldest fossils on Earth, dating back to about 2.5 million years, making them among the oldest organisms in the fossil record. They are found in the most diverse ecosystems in the world, including the ocean, rivers, lakes, ponds, soil, hot springs, and exists not only as single cell organisms, but can form colonies with varied roles. High concentrations of nutrients in water often cause blue-green algae blooms. Cyanobacteria are believed to have changed the early Earth’s atmosphere by increasing the amount of oxygen, and transforming the biodiversity of life on Earth.

Photosynthetic cyanobacteria

Cyanobacteria dominated the face of the Earth from about 2.5 to 2.2 billion years ago, and were responsible for the creation of most of the oxygen on the early history of the Earth. Cyanobacteria are photosynthetic, with the ability of converting the energy from the Sun and delivering oxygen like plants. Their ability to perform photosynthesis is believed to have changed the early reducing Earth’s atmosphere into an oxidizing one. This may have stimulated the evolution of eukaryotes. Unlike other photosynthetic organisms, cyanobacteria perform photosynthesis in the cytoplasm of the cell, rather than in the chloroplast. According to the endosymbiosis theory, chloroplasts in plants evolved through an endosymbiotic relationship between cyanobacteria and eukaryotic plants.

Fossil records

Cyanobacteria can be found in most habitats on Earth, including salt and fresh water bodies, tropical and Polar Regions. They may form biofilms in aquatic environments and live endosymbiotically within plants and lichens. Cyanobacteria may form colonies of filaments, with the ability to differentiate into distinct cell types, including heterocysts, which are nitrogen-fixing cells and akinetes, which are climate-resistant spores. Cyanobacteria often form microbial mats in shallow surface waters. These mat communities, over time, become stratified, then calcified and in the end, they become petrified. Stromatolites are fossilized microbial mats that contain a record of the earliest fossils on Earth.


Fossil records show that photosynthetic cyanobacteria first appeared at around 2.5 billion years ago, populating the earth in varied unicellular and multicellular forms. Scientists have discovered that the transition between unicellular and multicellular forms has occurred several times in the past. They have also found that the present single-celled cyanobacteria descend from multicellular organisms, suggesting that evolution doesn’t always occur from simple to complex organisms. Scientists believe that a better understanding of the way in which multicellularity evolved in blue-green algae, will help them better understand how complex organisms have evolved through life.

Algal blooms

Under certain conditions, cyanobacteria may reproduce explosively, resulting in algal blooms. Algal blooms can be harmful to humans and other animal species if there are toxins involved. Some species of cyanobacteria are known to produce toxins that can harm humans. People can be harmed by swallowing, direct contact or by breathing bacterial toxins contained in the air. Marine mammals and birds can die from drinking contaminated water during a blue-green algae bloom. Decayed bacterial blooms may deplete dissolved oxygen, killing fish. Also dense blue-green algae blooms may block out the sun’s energy, affecting other marine species.

Cyanobacteria are one of the most diverse microorganisms on Earth. They are found in a wide range of habitats of the world, such as in the world’s oceans and terrestrial ecosystems. They thrive in the most extreme habitats, such as hotsprings and Antarctica. They’re thought to have created the conditions in the early earth’s atmosphere for the evolution of oxygen, promoting biodiversity and eukaryotic photosynthesis. According to biomedcentral.com, a good understanding of when and how multicellularity evolved in ancient cyanobacteria may provide important data about the early history of life and expand our knowledge on other complex life forms.

More about this author: Jose Juan Gutierrez

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