Cyanobacteria, or “blue-green algae,” are single-celled organisms that create energy through photosynthesis and are found in aquatic or humid environments. They played a key role in the evolution of cellular life on Earth and are among the oldest things in the fossil record. Cyanobacteria can be harmful when they form toxic blooms, but individual cells are usually harmless.
The term “cyanobacteria” refers to a large group of single-celled organisms that have prehistoric roots but are still very abundant in modern times, usually in aquatic or humid environments. They are sometimes referred to as “blue-green algae” because large colonies of them in the water often look like algae, which are aquatic plants. However, there is no biological connection between bacteria and algae. Bacteria create energy through photosynthesis and live near the surface of most water. Oceans, rivers, streams and puddles host them; even some glaciers and mud have been found to contain small colonies. Many scientists believe that this type of bacteria played a key role in the evolution of cellular life on Earth.
Basic features
Individual cyanobacteria are microscopic, meaning they can’t be seen without the helicopter of a microscope or other magnifying tool. However, they are widely present in most of the planet’s water sources and often form visible colonies. These colonies, which are typically made up of millions of interconnected cells, sometimes resemble algae. The bacteria will bond with each other for a couple of different reasons, but when this happens it’s usually most visible near the surface of the water and tends to be bright blue in color. Cells are also this color individually, but it’s more noticeable when seen in a huge group.
Individual cells can vary in shape; most are thin and tubular, but some have a more flattened oval shape. They have an average length of about 2 millimeters and are generally very simple from a scientific point of view.
Different types
Based on their shape, known more formally as their “morphology”, cyanobacteria have been classified into five groups: chroococcoles, pleurocapsales, oscillatoriales, nostocales and stigonematales. However, the common lineage of only the latter two groups has been established. Just because two organisms are similar in shape, they are not necessarily phylogenetically related, meaning they may not be members of the same classification group known as a phylum.
Energy production
This type of bacteria creates its own energy and food through photosynthesis, like most plants. This means that cells are able to convert sunlight into energy which can be stored in the form of carbohydrates such as sugar. As a result, cells are almost entirely self-sufficient: they are able to create and store all the energy they need to thrive and reproduce.
Photosynthesis in cyanobacteria uses water as an electron donor and produces oxygen as a byproduct. Photosynthesis takes place in membranes called tilcoids, with chlorophyll used to absorb the sun’s rays. Unlike most other organisms which carry out photosynthesis in specialized organelles, these bacteria carry out the conversion directly in the cytoplasm of their cells.
Evolutionary history
Many evolutionary biologists argue that the chloroplasts found in most living plants are probably descended from or created by cyanobacteria. Considering they possess their own DNA, experts say it’s possible more sophisticated plant cells brought these bacteria into their structure long ago as a sort of mutually beneficial “symbiotic” relationship.
These organisms are very old, with some fossils dating back nearly 4 billion years to the Precambrian era. This makes them among the oldest things in the fossil record. Biologists generally believe that these organisms played a key role in increasing the amount of oxygen in the Earth’s atmosphere. Research has shown that, for nearly 2 billion years, these bacteria and other prokaryotes were the only organisms on Earth, as eukaryotes had not yet evolved. Conceivably, life on other plants, if it exists, may consist of prokaryotes such as cyanobacteria and not eukaryotes. Due to their simplicity, prokaryotic cells are approximately 1,000 times smaller than eukaryotic cells.
Health considerations
Occasionally, the bacteria will form large chains in the water and then begin to decompose or die. This causes the cells to fade, and the result is sometimes called a blue algae “bloom” due to its color and appearance. The blooms can be toxic to humans and animals, and people are usually discouraged from swimming in lakes and pools where the bacteria have been spotted in high concentrations like this. Individual cells are usually harmless and are often ingested or ingested without adverse consequences, even if they are weak, dying, or dead. Large strains, however, often contain high enough concentrations of nitrogen and other chemicals to damage the lungs and airways of the people who consume them. Specialized nitrogen-fixing bacteria are called heterocysts and these tend to be the most dangerous.
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