Cyanobacteria

As of 2014[update] the taxonomy was under revision[3][4] Cyanobacteria (/saɪˌænoʊbækˈtɪəri.ə/) are a group of autotrophic gram-negative bacteria[7] of the phylum Cyanobacteriota that can obtain biological energy via oxygenic photosynthesis.

[note 1] Cyanobacteria are probably the most numerous taxon to have ever existed on Earth and the first organisms known to have produced oxygen,[13] having appeared in the middle Archean eon and apparently originated in a freshwater or terrestrial environment.

[14][15] Their photopigments can absorb the red- and blue-spectrum frequencies of sunlight (thus reflecting a greenish color) to split water molecules into hydrogen ions and oxygen.

[17] The subsequent adaptation of early single-celled organisms to survive in oxygenous environments likely had led to endosymbiosis between anaerobes and aerobes, and hence the evolution of eukaryotes during the Paleoproterozoic.

[27] Some species are nitrogen-fixing and live in a wide variety of moist soils and water, either freely or in a symbiotic relationship with plants or lichen-forming fungi (as in the lichen genus Peltigera).

[32][33] Some cyanobacteria form harmful algal blooms causing the disruption of aquatic ecosystem services and intoxication of wildlife and humans by the production of powerful toxins (cyanotoxins) such as microcystins, saxitoxin, and cylindrospermopsin.

[39][40][41][42] From these lineages, nitrogen-fixing cyanobacteria are particularly important because they exert a control on primary productivity and the export of organic carbon to the deep ocean,[39] by converting nitrogen gas into ammonium, which is later used to make amino acids and proteins.

[41][42][43] While some planktonic cyanobacteria are unicellular and free living cells (e.g., Crocosphaera, Prochlorococcus, Synechococcus); others have established symbiotic relationships with haptophyte algae, such as coccolithophores.

[98] Cyanobacteria can interfere with water treatment in various ways, primarily by plugging filters (often large beds of sand and similar media) and by producing cyanotoxins, which have the potential to cause serious illness if consumed.

They are the most genetically diverse; they occupy a broad range of habitats across all latitudes, widespread in freshwater, marine, and terrestrial ecosystems, and they are found in the most extreme niches such as hot springs, salt works, and hypersaline bays.

[115][105] The relationships between cyanobionts (cyanobacterial symbionts) and protistan hosts are particularly noteworthy, as some nitrogen-fixing cyanobacteria (diazotrophs) play an important role in primary production, especially in nitrogen-limited oligotrophic oceans.

[119][120][121] Cyanobacteria, mostly pico-sized Synechococcus and Prochlorococcus, are ubiquitously distributed and are the most abundant photosynthetic organisms on Earth, accounting for a quarter of all carbon fixed in marine ecosystems.

For instance, billions of years ago, communities of marine Paleoproterozoic cyanobacteria could have helped create the biosphere as we know it by burying carbon compounds and allowing the initial build-up of oxygen in the atmosphere.

[36] Extreme blooms can also deplete water of oxygen and reduce the penetration of sunlight and visibility, thereby compromising the feeding and mating behaviour of light-reliant species.

As with other kinds of bacteria,[137] certain components of the pili may allow cyanobacteria from the same species to recognise each other and make initial contacts, which are then stabilised by building a mass of extracellular polysaccharide.

[127] The bubble flotation mechanism identified by Maeda et al. joins a range of known strategies that enable cyanobacteria to control their buoyancy, such as using gas vesicles or accumulating carbohydrate ballasts.

Evidence supports the existence of controlled cellular demise in cyanobacteria, and various forms of cell death have been described as a response to biotic and abiotic stresses.

However, cell death research in cyanobacteria is a relatively young field and understanding of the underlying mechanisms and molecular machinery underpinning this fundamental process remains largely elusive.

and Spirulina subsalsa found in the hypersaline benthic mats of Guerrero Negro, Mexico migrate downwards into the lower layers during the day in order to escape the intense sunlight and then rise to the surface at dusk.

A step-up photophobic reaction occurs when an organism enters a brighter area field from a darker one and then reverses direction, thus avoiding the bright light.

[26] Stromatolites are layered biochemical accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by biofilms (microbial mats) of microorganisms, especially cyanobacteria.

[204] The description of another independent and more recent primary endosymbiosis event between a cyanobacterium and a separate eukaryote lineage (the rhizarian Paulinella chromatophora) also gives credibility to the endosymbiotic origin of the plastids.

For bacterial transformation to take place, the recipient bacteria must be in a state of competence, which may occur in nature as a response to conditions such as starvation, high cell density or exposure to DNA damaging agents.

[228] "Vampirovibrionales" Gloeobacterales "Thermosynechococcales" Synechococcales Pleurocapsales Spirulinales Chroococcales Oscillatoriales Nostocales "Saganbacteria" (WOR1) "Marinamargulisbacteria" "Riflemargulisbacteria" (GWF2_35_9) "Termititenacia" "Caenarcanales" "Obscuribacterales" "Vampirovibrionales" "Gastranaerophilales" UBA7694 ("Blackallbacteria") S15B-MN24 ("Sericytochromatia"; "Tanganyikabacteria") Gloeobacterales Thermostichales Pseudanabaenales Gloeoemargaritales Prochlorococcaceae {PCC-6307} "Acaryochloridales" "Limnotrichales" Prochlorotrichales Synechococcales "Phormidesmiales" "Nodosilineales" Oculatellales "Elainellales" "Leptolyngbyales" Cyanobacteriales Historically, bacteria were first classified as plants constituting the class Schizomycetes, which along with the Schizophyceae (blue-green algae/Cyanobacteria) formed the phylum Schizophyta,[235] then in the phylum Monera in the kingdom Protista by Haeckel in 1866, comprising Protogens, Protamaeba, Vampyrella, Protomonae, and Vibrio, but not Nostoc and other cyanobacteria, which were classified with algae,[236] later reclassified as the Prokaryotes by Chatton.

[242] The currently accepted taxonomy as of 2025 is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)[243] and National Center for Biotechnology Information (NCBI).

[261] Researchers from several space agencies argue that cyanobacteria could be used for producing goods for human consumption in future crewed outposts on Mars, by transforming materials available on this planet.

[265] Sulfate polysaccharides exhibit immunomodulatory, antitumor, antithrombotic, anticoagulant, anti-mutagenic, anti-inflammatory, antimicrobial, and even antiviral activity against HIV, herpes, and hepatitis.

Several cases of human poisoning have been documented, but a lack of knowledge prevents an accurate assessment of the risks,[267][268][269][270] and research by Linda Lawton, FRSE at Robert Gordon University, Aberdeen and collaborators has 30 years of examining the phenomenon and methods of improving water safety.

[271] Recent studies suggest that significant exposure to high levels of cyanobacteria producing toxins such as BMAA can cause amyotrophic lateral sclerosis (ALS).

[280] Increased thermal stratification of lakes and reservoirs enables buoyant cyanobacteria to float upwards and form dense surface blooms, which gives them better access to light and hence a selective advantage over nonbuoyant phytoplankton organisms.

Cyanobacteria are found almost everywhere. Sea spray containing marine microorganisms , including cyanobacteria, can be swept high into the atmosphere where they become aeroplankton , and can travel the globe before falling back to earth. [ 22 ]
Prochlorococcus , an influential marine cyanobacterium which produces much of the world's oxygen
Morphological variations [ 52 ]
• Unicellular: (a) Synechocystis and (b) Synechococcus elongatus
• Non- heterocytous : (c) Arthrospira maxima ,
(d) Trichodesmium and (e) Phormidium
• False- or non-branching heterocytous: (f) Nostoc
and (g) Brasilonema octagenarum
• True-branching heterocytous: (h) Stigonema
(ak) akinetes (fb) false branching (tb) true branching
Nitrogen-fixing cyanobacteria
Diagram of a typical cyanobacterial cell
Cyanobacterial thylakoid membrane [ 66 ]
Outer and plasma membranes are in blue, thylakoid membranes in gold, glycogen granules in cyan, carboxysomes (C) in green, and a large dense polyphosphate granule (G) in pink
Environmental impact of cyanobacteria and other photosynthetic microorganisms in aquatic systems. Different classes of photosynthetic microorganisms are found in aquatic and marine environments where they form the base of healthy food webs and participate in symbioses with other organisms. However, shifting environmental conditions can result in community dysbiosis, where the growth of opportunistic species can lead to harmful blooms and toxin production with negative consequences to human health, livestock and fish stocks. Positive interactions are indicated by arrows; negative interactions are indicated by closed circles on the ecological model. [ 93 ]
Diagnostic Drawing: Cyanobacteria associated with tufa: Microcoleus vaginatus
Symbiosis with land plants [ 105 ]
Leaf and root colonization by cyanobacteria
(1) Cyanobacteria enter the leaf tissue through the stomata and colonize the intercellular space, forming a cyanobacterial loop.
(2) On the root surface, cyanobacteria exhibit two types of colonization pattern; in the root hair , filaments of Anabaena and Nostoc species form loose colonies, and in the restricted zone on the root surface, specific Nostoc species form cyanobacterial colonies.
(3) Co-inoculation with 2,4-D and Nostoc spp. increases para-nodule formation and nitrogen fixation. A large number of Nostoc spp. isolates colonize the root endosphere and form para-nodules. [ 105 ]
Cyanobionts of Ornithocercus dinoflagellates [ 106 ]
Live cyanobionts (cyanobacterial symbionts) belonging to Ornithocercus dinoflagellate host consortium
(a) O. magnificus with numerous cyanobionts present in the upper and lower girdle lists (black arrowheads) of the cingulum termed the symbiotic chamber.
(b) O. steinii with numerous cyanobionts inhabiting the symbiotic chamber.
(c) Enlargement of the area in (b) showing two cyanobionts that are being divided by binary transverse fission (white arrows).
Epiphytic Calothrix cyanobacteria (arrows) in symbiosis with a Chaetoceros diatom. Scale bar 50 μm.
Collective behaviour and buoyancy strategies in single-celled cyanobacteria [ 127 ]
Model of a clumped cyanobacterial mat [ 130 ]
Light microscope view of cyanobacteria from a microbial mat
Cell death in eukaryotes and cyanobacteria [ 29 ]
Types of cell death according to the Nomenclature Committee on Cell Death (upper panel; [ 133 ] and proposed for cyanobacteria (lower panel). Cells exposed to extreme injury die in an uncontrollable manner, reflecting the loss of structural integrity. This type of cell death is called "accidental cell death" (ACD). "Regulated cell death (RCD)" is encoded by a genetic pathway that can be modulated by genetic or pharmacologic interventions. Programmed cell death (PCD) is a type of RCD that occurs as a developmental program, and has not been addressed in cyanobacteria yet. RN, regulated necrosis.
The hypothetical conceptual model coupling programmed cell death (PCD) and the role of microcystins (MCs) in Microcystis. (1) The extracellular stressor (e.g., ultraviolet radiation) acts on the cell. (2) Intracellular oxidative stress increases; the intracellular reactive oxygen species (ROS) content exceeds the antioxidative capacity of the cell (mediated mostly by an enzymatic system involving a superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX)) and causes molecular damage. (3) The damage further activates the caspase-like activity, and apoptosis-like death is initiated. Simultaneously, intracellular MCs begin to be released into the extracellular environment. (4) The extracellular MCs have been significantly released from dead Microcystis cells. (5) They act on the remaining Microcystis cells, and exert extracellular roles, for example, extracellular MCs can increase the production of extracellular polysaccharides (EPS) that are involved in colony formation. Eventually, the colonial form improves the survival of the remaining cells under stressful conditions. [ 140 ]
Synechococcus uses a gliding technique to move at 25 μm/s. Scale bar is about 10 μm.
Timing and trends in cell diameter, loss of filamentous forms and habitat preference within cyanobacteria
Based on data: nodes (1–10) and stars representing common ancestors from Sánchez-Baracaldo et al., 2015, [ 47 ] timing of the Great Oxidation Event (GOE), [ 211 ] the Lomagundi-Jatuli Excursion , [ 212 ] and Gunflint formation . [ 213 ] Green lines represent freshwater lineages and blue lines represent marine lineages are based on Bayesian inference of character evolution (stochastic character mapping analyses). [ 47 ]
Taxa are not drawn to scale – those with smaller cell diameters are at the bottom and larger at the top
Tree of Life in Generelle Morphologie der Organismen (1866). Note the location of the genus Nostoc with algae and not with bacteria (kingdom "Monera")
Cyanobacteria cultured in specific media: Cyanobacteria can be helpful in agriculture as they have the ability to fix atmospheric nitrogen in soil.
Spirulina tablets