Cyanobacteria

Tiny living things live in the water.

They are a blue-green color. They use sunlight to make food.

This light helps them change air into food. They also make the air we breathe. This helped the Earth a long time ago. They can live in many places. Some live in hot springs. Others live in the cold polar regions. They are found almost everywhere on our planet.

These small things are very important to our world.

Cyanobacteria are tiny living things. They are often called blue-green algae.

They have a bluish-green color. This color comes from special parts called pigments. These pigments catch sunlight to make food. This way of making food is called photosynthesis.

Cyanobacteria do something very special. They use sunlight to split water. This process lets out oxygen. Long ago, the Earth had very little oxygen. Cyanobacteria made much more of it. This changed the air on our planet forever.

These tiny cells live in many places. They live in hot springs and cold polar regions. Some live in the ocean. A tiny group called Prochlorococcus lives in the sea. It is the smallest known maker of food. One single milliliter of seawater can have 100,000 of them! They are very important to the ocean. Some cyanobacteria can also make toxins. These toxins can be bad for animals and people.

Cyanobacteria are tiny living things that play a huge role in our world. They are often called blue-green algae because of their bluish-green color.

These organisms are special because they can make their own food using sunlight. This way of making food is called oxygenic photosynthesis. They use light to turn water and carbon dioxide into energy. This process also releases oxygen into the air.

Because they make food from light, they are called autotrophs. This ability has helped them live on Earth for a very long time.

How does this amazing thing work? Inside the cell, there are flattened sacs called thylakoids.

These sacs hold the pigments needed to catch sunlight. The pigments absorb red and blue light from the sun. This energy is used to split water molecules apart. This action creates hydrogen ions and releases oxygen as a byproduct. The cell then uses the hydrogen to turn carbon dioxide into carbohydrates. These carbohydrates are complex organic compounds that the cell uses for food.

Scientists believe cyanobacteria are some of the oldest living things on Earth. They first appeared during the middle Archean eon. Fossil records show they have existed for at least 2.1 billion years. Long ago, the Earth's atmosphere did not have much oxygen. By releasing oxygen for billions of years, cyanobacteria changed the whole planet. This caused the Great Oxidation Event. This event turned the air into an oxidizing one. It even caused what some call the "rusting of the Earth."

There are many different kinds of cyanobacteria found in many places. Some live in hot springs, deserts, or even the polar regions.

One very important group is called Prochlorococcus. It is the smallest known photosynthetic organism. It is only 0.5 to 0.8 micrometres across.

You might find 100,000 of these cells in just one milliliter of seawater. There are estimated to be several octillion of them on Earth. This single group is responsible for about 20% of the oxygen in our atmosphere.

Cyanobacteria are linked to many things you see every day. Some species live in a helpful relationship with plants or fungi.

For example, some can act as a natural fertilizer for rice. However, some cyanobacteria can also be dangerous. They can produce toxins called cyanotoxins.

These toxins can make humans and animals sick during harmful blooms. Even so, they remain a fundamental part of the food web in our oceans.

Cyanobacteria are a massive group of autotrophic, gram-negative bacteria. They belong to the phylum Cyanobacteriota. These organisms are unique because they perform oxygenic photosynthesis. This means they use sunlight to create biological energy. They are often called blue-green algae because of their cyan color.

Scientists believe they are the most numerous taxon to ever exist on Earth. They are essential to the planet's life-support systems. They act as primary producers in many environments.

The process of photosynthesis in cyanobacteria is highly specialized. It happens inside internal membranes called thylakoids. These are flattened sacs located within the cell.

Photopigments like chlorophyll, carotenoids, and phycobilins absorb sunlight. Specifically, they absorb red- and blue-spectrum frequencies. This absorption allows them to split water molecules. This splitting produces hydrogen ions and oxygen. The oxygen is released into the environment as a byproduct. The hydrogen ions then react with carbon dioxide. This reaction is called carbon fixation. It produces complex organic compounds like carbohydrates. To make this efficient, many species use carboxysomes. These are cage-like protein structures that concentrate carbon dioxide. They hold the enzyme RuBisCO to increase efficiency.

Cyanobacteria show incredible variety in their physical forms, or morphology. Some are unicellular, meaning they are single cells. Others are filamentous, forming long chains of cells.

Some filamentous species show the first signs of multicellularity. They can develop specialized cells for different tasks. Vegetative cells perform normal photosynthesis. Akinetes are thick-walled spores that resist harsh climates. Heterocysts are specialized cells used for nitrogen fixation. These cells are vital because they create an anaerobic environment. This protects the enzyme nitrogenase, which is sensitive to oxygen. Some species also form hormogonia. These are motile filaments that move to form new colonies.

The history of cyanobacteria is tied to the history of Earth itself. They likely originated in freshwater or terrestrial environments. They first appeared during the middle Archean eon. Fossil records show they have existed for at least 2.1 billion years. Before cyanobacteria, Earth's atmosphere was anoxic. This means it lacked free gaseous oxygen. By releasing oxygen for billions of years, cyanobacteria changed the atmosphere. This led to the Great Oxidation Event. This event caused the "rusting of the Earth" during the early Proterozoic. This change allowed for the evolution of eukaryotes. This happened through endosymbiosis, where one cell lives inside another.

The scale of cyanobacterial populations is staggering. One genus, Prochlorococcus, is the smallest known photosynthetic organism. It measures only 0.5 to 0.8 micrometres across.

Despite their size, they are incredibly abundant. A single milliliter of surface seawater can hold 100,000 cells. There are an estimated several octillion individuals worldwide. This group alone accounts for about 20% of Earth's atmospheric oxygen. In the oceans, cyanobacteria contribute about 25% of global marine primary production. They are a fundamental part of marine food webs.

While many cyanobacteria are helpful, some can be dangerous. Certain species produce powerful toxins called cyanotoxins. Examples include microcystins, saxitoxin, and cylindrospermopsin.

These toxins can cause harmful health effects in humans and animals. When these organisms grow rapidly, they create harmful algal blooms. These blooms can disrupt aquatic ecosystems and cause intoxication in wildlife. However, many species are used in biotechnology. They are studied for bioethanol production and food colorings. They can even serve as dietary supplements or raw materials.

Cyanobacteria are deeply connected to other biological systems. Many eukaryotic organisms, like red and green algae, have ancestors in cyanobacteria. Through endosymbiosis, cyanobacteria evolved into specialized organelles called plastids. These include chloroplasts, chromoplasts, etioplasts, and leucoplasts.

Some cyanobacteria also live in symbiotic relationships with plants. For instance, Anabaena lives with the aquatic fern Azolla. This relationship can provide rice plantations with biofertilizer. Others live in symbiosis with lichen-forming fungi. They are truly global players in biogeochemical cycles.