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Despite the important role they play in ecosystems, we hear little about cyanobacteria or oxyphotobacteria. At Ecologist Verde we want to dedicate this article to these fascinating microorganisms that make life on Earth possible. Did you know that cyanobacteria were originally included in the Plantae kingdom, that of plants, and were called cyanophytes? And that later they were considered algae and we called them cyanophytes? Currently, they are located in the Monera kingdom.
Keep reading this interesting article and discover more about what are cyanobacteria, their characteristics and examples of these, as well as its great importance for life.
What are cyanobacteria
Cyanobacteria u oxyphotobacteria are a phylum of prokaryotic, autotrophic and unicellular organisms capable of carrying out the oxygenic photosynthesis. They belong to the group of gram negative bacteria and its name can be translated as “blue bacteria”, since the prefix cyano- refers to its characteristic bluish color.
Cyanobacteria were originally included in the plant kingdom and were called cyanophytes, which means blue plants. Later, they began to be considered algae and to be called cyanophytes, which means blue algae. Cyanobacteria were believed to be algae due to their photosynthetic capacity, but later, the term algae was redefined and reserved exclusively for photosynthetic eukaryotic organisms, with cyanobacteria excluded from this group as prokaryotic organisms.
Currently, cyanobacteria are grouped in the Cyanophyceae class of the Bacteria domain, belonging to the already disused Monera kingdom. They are still known as blue-green algae despite the fact that, as we have already established, they are not algae but bacteria. We can say, then, that the kingdom of cyanobacteria is the kingdom Monera (which includes the Archaea and Bacteria domains and is in disuse, since prokaryotic organisms are not classified into kingdoms taxonomically).
Characteristics of cyanobacteria
We start by indicating the main characteristics of cyanobacteria to get to know them better little by little:
- They are the only prokaryotes capable of performing the oxygenic photosynthesis. A prokaryote or prokaryotic organism is one that is composed of prokaryotic cells, which do not have a defined cell nucleus. Oxygenic photosynthesis is one in which electrons from water are used to convert light energy into chemical energy and inorganic chemical compounds, such as carbon dioxide, nitrogen or phosphorus, into organic chemical compounds such as oxygen.
- Another distinctive feature of cyanobacteria is their striking teal color, which ranges from a very faint green to a blue color so dark that it resembles black. This pigmentation is due to phycobilin, a class of chromophore compounds present in the cytoplasm of cyanobacteria. Despite the fact that, as its name indicates, the most common colors in cyanobacteria are those that derive from blue-green, there are numerous species that present reddish or copper tones.
- Although cyanobacteria are microscopic organisms only a few micrometers in length, they are considerably larger than most bacteria.
- They reproduce asexually (by binary fission, multiple fission, budding, or fragmentation).
- They have aerobic respiration.
- Although they are unicellular organisms, they tend to group together and form colonies extensive, even ranging from the thousands to the millions of individuals grouped in colonial associations.
- Cyanobacteria inhabit all types of ecosystems aquatic and terrestrial ecosystems with acceptable levels of humidity. Cyanobacteria can be found in ponds, lakes, lagoons, rivers, wetlands, mangroves, oceans, underground water reservoirs, caves, jungles, mountains, forests, the surface of rock formations, the skin of some animals, and even cyanobacteria often appear in aquariums, tanks and fountains. Some cyanobacteria are extremophiles (they endure extreme environmental conditions) and live in environments as inhospitable as deserts, hot springs, hydrothermal vents, glaciers, hypersaline lakes, highly alkaline waters and even in outer space.
- There are species of cyanobacteria that establish symbiotic relationships with ferns, protists or fungi. The symbiosis between a cyanobacterium and a fungus is commonly known as lichen.
Although most cyanobacteria have the characteristics mentioned above, there are certain exceptions. There are species of cyanobacteria that, for example, are macroscopic and not microscopic or heterotrophic and not autotrophic.
Organelles of cyanobacteria
Although we have already indicated the main characteristics, we delved deeper into the traits of these small organisms and talked about the organelles of cyanobacteria:
- Carboxysomes: they are responsible for the fixation of CO2.
- Gas vesicles: allow buoyancy.
- Cyanophycin granules: store cyanophycin protein and cyanophytic starch.
- Glycogen granules: store energy.
- Protonucleus: represents the region in which the cyanobacterial DNA is found, which is characterized by being circular, closed and naked.
- Thylakoid membrane: it is an invagination of the plasma membrane in which the thylakoids are found.
- Ribosomes: allow protein synthesis and measure 70 s.
- Cell membrane: it is made up of an inner plasma membrane and an outer membrane, both composed of phospholipids and hopanoids.
- Cell wall: located between the inner and outer plasma membranes, it is composed of peptidoglycans and provides mechanical protection to the cell.
- Photosynthetic lamellae: contain photosynthetic pigments such as chlorophyll a, carotenoids and phycobilins.
Cyanobacteria groups
The groups that make up these microorganisms are called trimeric colonies (because they grow and branch in three directions) and are composed of highly specialized cells that fulfill specific functions within the colony. Some of the cells that make up the trimeric cyanobacterial colonies are:
- Heterocysts: they are the cells in charge of fixing atmospheric nitrogen.
- Acinetos: these are the largest cells and are used to store cyanophilic starch.
- Beocysts: they are cells in charge of the branching of the colony through multiple fission.
- Nedridiums: they are cells that make apostosis to allow the spread of the colonies. These cells die and allow segments of the colony (hormogoria) to detach and move until they find a new substrate in which they can fixate and form a new colony.
Examples of cyanobacteria
exist more than 5,000 species of cyanobacteria. Some of the most representative species are:
- Arthrospira platensis and Arthrospira maxima: belonging to the genus Spirulina, they are two species of cyanobacteria of commercial interest. They are used in the production of spirulina, an energizing dietary supplement with a high content of proteins, minerals, vitamins and carotenes.
- Nostoc sphaericum: it is a cyanobacterium of the Nostoc genus highly appreciated in the gastronomy of several Latin American countries, where it is known as cushuro. It has a spherical shape, a gelatinous consistency, and antioxidant and antiviral properties, which is why it is also of pharmacological interest.
- Nostoc commune.
- Punctiform nostoc.
- Synechococcus.
What is the importance of cyanobacteria for life
To finish commenting on the interesting world of cyanobacteria, here we mention various aspects for which they are considered super important for life as we know it today.
- Cyanobacteria play a fundamental role in the development of various aquatic and terrestrial ecosystems. Are primary producers and they act like nitrogen fixers and suppliers for all types of food chains. Atmospheric nitrogen is especially important for the growth of algae and aquatic plants, which are themselves important primary producers. Here you can get to know them better: Producer organizations: what they are and examples.
- Since most of Earth's photosynthetic activity occurs in water, algae and cyanobacteria are known to produce much more oxygen than land plants. Cyanobacteria generate a good percentage of oxygen molecular structure of the Earth and, in addition, they help enormously lower carbon dioxide levels in the environment.
- Cyanobacteria were the first autotrophic organisms and, in prehistoric times, they gradually flooded the earth's atmosphere with oxygen that they produced through photosynthesis. This change in the composition of the atmosphere allowed the formation of the ozone layer (which protects us from the harmful ultraviolet radiation of the Sun) and the emergence and diversification of new organisms capable of surviving outside of water: aerobic beings. Thanks to cyanobacteria, autotrophic organisms originated. From the endosymbiosis between the plastids of cyanobacteria and primitive eukaryotic cells arise the plant cells and algae that we know today. Here you can read about the Origin and evolution of plants: summary.
- Several species of cyanobacteria are of economic and biotechnological interest. Some are grown for food, for example Arthrospira platensis, Arthrospira maxima and Nostoc sphaericum.
- Many cyanobacteria are pollution indicators and they become a real problem for their ecosystems. When there is eutrophication (excess of nutrients such as phosphorus, nitrogen and sulfur in bodies of water), cyanobacteria increase their population uncontrollably. These gigantic colonies clump together in thick, slimy layers on the surface of rivers, lakes, and ponds and are known as cyanobacterial blooms. These harm many living beings because they prevent sunlight from reaching the water bottom and produce toxins that can be deadly even to humans. They also harm human activities such as fishing, transportation and tourism and contaminate drinking water sources. Many times this excess of phosphorus, nitrogen and / or sulfur in water bodies is due to human activities such as agriculture and livestock, which use fertilizers and pesticides with high contents of these bioelements. Here you can read about Environmental indicators: what they are, types and examples and about What is eutrophication.
- The appearance of cyanobacteria in an aquarium or tank can mean poor maintenance, excess nutrients (sulfates, nitrates, and phosphates), poor lighting, stagnation, and / or poor water filtration.
- When cyanobacteria form lichens they are used as biological indicators of air and water quality because they only grow in environments with very low or zero levels of contamination.
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