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Cyanobacterial morphology refers to the form or shape of cyanobacteria.
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue ...
are a large and diverse phylum of bacteria defined by their unique combination of
pigments A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
and their ability to perform oxygenic photosynthesis. Cyanobacteria often live in colonial aggregates that can take a multitude of forms. Of particular interest among the many species of cyanobacteria are those that live colonially in elongate hair-like structures, known as
trichomes Trichomes (); ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plan ...
. These filamentous species can contain hundreds to thousands of cells. They often dominate the upper layers of
microbial mat A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in desert ...
s found in extreme environments such as
hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by ci ...
s, hypersaline water, deserts and polar regions, as well as being widely distributed in more mundane environments. Many filamentous species are also
motile Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...
,
gliding Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word ''soaring'' is ...
along their long axis, and displaying photomovement by which a trichome modulates its gliding according to the incident light. The latter has been found to play an important role in guiding the trichomes to optimal lighting conditions, which can either inhibit the cells if the incident light is too weak, or damage the cells if too strong.


Diversity of forms

Cyanobacteria present remarkable variability in terms of morphology: from
unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...
and colonial to multicellular filamentous forms. Their cell size varies from less than 1 µm in diameter (picocyanobacteria) up to 100 µm (some tropical forms in the genus ''
Oscillatoria ''Oscillatoria'' is a genus of filamentous cyanobacterium which is often found in freshwater environments, such as hot springs, and appears blue-green. Its name refers to the oscillating motion of its filaments as they slide against each other ...
'') Filamentous forms exhibit functional cell differentiation such as
heterocyst Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as '' Nostoc punctiforme'', '' Cylindrospermum stagnale'', and ''Anabaena sphaerica''. They fix nitrogen f ...
s (for nitrogen fixation), akinetes (resting stage cells), and
hormogonia Hormogonia are motile filaments of cells formed by some cyanobacteria in the order Nostocales and Stigonematales. They are formed during vegetative reproduction in unicellular, filamentous cyanobacteria, and some may contain heterocysts and akin ...
(reproductive, motile filaments). These, together with the intercellular connections they possess, are considered the first signs of multicellularity. Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
Many cyanobacteria form motile filaments of cells, called
hormogonia Hormogonia are motile filaments of cells formed by some cyanobacteria in the order Nostocales and Stigonematales. They are formed during vegetative reproduction in unicellular, filamentous cyanobacteria, and some may contain heterocysts and akin ...
, that travel away from the main biomass to bud and form new colonies elsewhere. The cells in a hormogonium are often thinner than in the vegetative state, and the cells on either end of the motile chain may be tapered. To break away from the parent colony, a hormogonium often must tear apart a weaker cell in a filament, called a necridium.


Colonial and unicellular

In aquatic habitats, unicellular cyanobacteria are considered as an important group regarding abundance, diversity, and ecological character. Unicellular cyanobacteria have spherical, ovoid, or cylindrical cells that may aggregate into irregular or regular colonies bound together by the mucous matrix (
mucilage Mucilage is a thick, gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of m ...
) secreted during the growth of the colony. Based on the species, the number of cells in each colony may vary from two to several thousand. Each individual cell (each single cyanobacterium) typically has a thick, gelatinous
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mec ...
. They lack
flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...
, but hormogonia of some species can move about by
gliding Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word ''soaring'' is ...
along surfaces. File:Merismopedia.jpg, '' Merismopedia'' forms rectangular colonies held together by a mucilaginous matrix. Species in this genus divide in only two directions, creating a characteristic grid-like pattern arranged in rows and flats. File:CyanobacteriaColl1.jpg, Colonies of '' Nostoc pruniforme'' "jelly balls" File:Colonial-cyanobacteria-of-the-Stratonostoc-species-on-the-coast-of-the-Barguzinsky-Bay-of-Lake-Baikal.jpg, Colonial cyanobacteria ''Stratonostoc'' File:Gloeotrichia in Sytox.jpg, Ball-shaped colony of Gloeotrichia echinulata File:Lyngbya majuscula.jpg, Cyanobacterial colony of ''
Lyngbya majuscula ''Lyngbya majuscula'' is a species of filamentous cyanobacteria in the genus ''Lyngbya''. It is named after the Dane Hans Christian Lyngbye. As a result of recent genetic analyses, several new genera were erected from the genus ''Lyngbya'': ...
''


Filamentous and multicellular

File:Filamentous cyanobacteria structure of Oscillatoria lutea.jpg, Example of filamentous cyanobacteria structure ('' Oscillatoria lutea'') showing a reticulate pattern Some filamentous species can differentiate into several different
cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
types: * vegetative cells – the normal, photosynthetic cells that are formed under favorable growing conditions *
akinete An akinete is an enveloped, thick-walled, non-motile, dormant cell formed by filamentous, heterocyst-forming cyanobacteria under the order Nostocales and Stigonematales. Akinetes are resistant to cold and desiccation. They also accumulate and sto ...
s – climate-resistant spores that may form when environmental conditions become harsh * thick-walled
heterocysts Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as '' Nostoc punctiforme'', ''Cylindrospermum stagnale'', and ''Anabaena sphaerica''. They fix nitrogen fr ...
– which contain the enzyme
nitrogenase Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the Organic redox reaction, reduction of nitrogen (N2) to ammonia (NH3). Nitrog ...
vital for
nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. A ...
in an anaerobic environment due to its sensitivity to oxygen. Many of the multicellular filamentous forms of ''
Oscillatoria ''Oscillatoria'' is a genus of filamentous cyanobacterium which is often found in freshwater environments, such as hot springs, and appears blue-green. Its name refers to the oscillating motion of its filaments as they slide against each other ...
'' are capable of a waving motion; the filament oscillates back and forth. In water columns, some cyanobacteria float by forming gas vesicles, as in
archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archae ...
. These vesicles are not
organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...
s as such. They are not bounded by lipid membranes but by a protein sheath. File:Anabaena sperica2.jpg, '' Anabaena sperica'' File:Necklace of Mermaid.tif, ''
Anabaena ''Anabaena'' is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern. They are one of four genera of cyanob ...
'' is used as a
model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the working ...
to study simple vision File:Cyanobacteria.jpg, Helical filaments of cyanobacteria File:Dolichospermum sp.cropped-brighter.jpg, Helical filament from '' Dolichospermum'' File:Lyngbya.jpg, ''
Lyngbya ''Lyngbya'' is a genus of cyanobacteria, unicellular autotrophs that form the basis of the oceanic food chain. As a result of recent genetic analyses, several new genera were erected from this genus: ''e.g.'', '' Moorea'', '' Limnoraphis'', ' ...
'' species form long, unbranching filaments inside rigid
mucilaginous Mucilage is a thick, gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of m ...
sheaths which can form tangles or mats, intermixed with other phytoplankton species


Branched

File:Cyanobacteriabranchedforms026 Fischerella.jpg, ''
Fischerella ''Fischerella'' is a genus of cyanobacteria belonging to the family Hapalosiphonaceae. The genus was first described by M. Gomont in 1895. The genus has cosmopolitan distribution. The genus name of ''Deightoniella'' is in honour of Christian ...
'' File:Fischerella thermalis.png, True branching phenotype of a '' Fischerella thermalis'' colony


Heterocysts

Heterocyst Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as '' Nostoc punctiforme'', '' Cylindrospermum stagnale'', and ''Anabaena sphaerica''. They fix nitrogen f ...
s are specialized
nitrogen-fixing Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
cells formed during nitrogen starvation by some filamentous cyanobacteria, such as '' Nostoc punctiforme'', ''
Cylindrospermum ''Cylindrospermum'' is a genus of filamentous cyanobacteria found in terrestrial and aquatic environments. In terrestrial ecosystems, ''Cylindrospermum'' is found in soils, and in aquatic ones, it commonly grows as part of the periphyton on aq ...
stagnale'', and ''
Anabaena ''Anabaena'' is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern. They are one of four genera of cyanob ...
sphaerica''. They fix nitrogen from atmospheric N2 using the
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...
nitrogenase Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the Organic redox reaction, reduction of nitrogen (N2) to ammonia (NH3). Nitrog ...
, in order to provide the cells in the filament with nitrogen for biosynthesis.


Movement

Cyanobacteria are ubiquitous, finding habitats in most water bodies and in extreme environments such as the polar regions, deserts, brine lakes and hot springs. They have also evolved surprisingly complex collective behaviours that lie at the boundary between single-celled and multicellular life. For example, filamentous cyanobacteria live in long chains of cells that bundle together into larger structures including
biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular p ...
s, biomats and
stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). The ...
s. These large colonies provide a rigid, stable and long-term environment for their communities of bacteria. In addition, cyanobacteria-based biofilms can be used as
bioreactor A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances ...
s to produce a wide range of chemicals, including biofuels like biodiesel and ethanol. However, despite their importance to the history of life on Earth, and their commercial and environmental potentials, there remain basic questions of how filamentous cyanobacteria move, respond to their environment and self-organize into collective patterns and structures. Modified text was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
All known cyanobacteria lack
flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...
; however, many filamentous species move on surfaces by gliding, a form of locomotion where no physical appendages are seen to aid movement. The actual mechanism behind gliding is not fully understood, although over a century has elapsed since its discovery. One theory suggests that gliding motion in cyanobacteria is mediated by the continuous secretion of
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...
s through pores on individual cells. Another theory suggests that gliding motion involves the use of
type IV pili A pilus (Latin for 'hair'; plural: ''pili'') is a hair-like appendage found on the surface of many bacteria and archaea. The terms ''pilus'' and '' fimbria'' (Latin for 'fringe'; plural: ''fimbriae'') can be used interchangeably, although some r ...
, polymeric assemblies of the protein
pilin Pilin refers to a class of fibrous proteins that are found in pilus structures in bacteria. These structures can be used for the exchange of genetic material, or as a cell adhesion mechanism. Although not all bacteria have pili or fimbriae, bact ...
, as the driving engines of motion. However, it is not clear how the action of these pili would lead to motion, with some suggesting they retract, while others suggest they push, to generate forces. Other scholars have suggested
surface wave In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occur within liquids, at th ...
s generated by the contraction of a fibril layer as the mechanism behind gliding motion in ''Oscillatoria''. Recent work also suggests that shape fluctuations and capillary forces could be involved in gliding motion. Through collective interaction, filamentous cyanobacteria self-organize into colonies or biofilms, symbiotic communities found in a wide variety of ecological niches. Their larger-scale collective structures are characterized by diverse shapes including bundles,
vortice ''Vortice'' (i.e. "Vortex") is a 1953 Italian melodrama film directed by Raffaello Matarazzo and starring Massimo Girotti and Silvana Pampanini. Plot Cast *Massimo Girotti as Guido Aureli * Silvana Pampanini as Elena Fanti *Franco Fabri ...
s and
reticulate Reticulation is a net-like pattern, arrangement, or structure. Reticulation or Reticulated may refer to: * Reticulation (single-access key), a structure of an identification tree, where there are several possible routes to a correct identificat ...
patterns. Similar patterns have been observed in fossil records. For filamentous cyanobacteria, the mechanics of the filaments is known to contribute to self-organization, for example in determining how one filament will bend when in contact with other filaments or obstacles. Further, biofilms and biomats show some remarkably conserved macro-mechanical properties, typically behaving as
viscoelastic In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like water, resist shear flow and strain linearly ...
materials with a relaxation time of about 20 min. Cyanobacteria have strict light requirements. Too little light can result in insufficient energy production, and in some species may cause the cells to resort to heterotrophic respiration. Too much light can inhibit the cells, decrease photosynthesis efficiency and cause damage by bleaching. UV radiation is especially deadly for cyanobacteria, with normal solar levels being significantly detrimental for these microorganisms in some cases. Filamentous cyanobacteria that live in microbial mats often migrate vertically and horizontally within the mat in order to find an optimal niche that balances their light requirements for photosynthesis against their sensitivity to photodamage. For example, the filamentous cyanobacteria Oscillatoria sp. 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. In contrast, the population of Microcoleus chthonoplastes found in hypersaline mats at Salin-de-Giraud, Camargue, France migrate to the upper layer of the mat during the day and are spread homogenously through the mat at night. An in vitro experiment using P. uncinatum also demonstrated this species' tendency to migrate in order to avoid damaging radiation. These migrations are usually the result of some sort of photomovement, although other forms of taxis can also play a role. Many species of cyanobacteria are capable of gliding.
Gliding Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word ''soaring'' is ...
is a form of cell movement that differs from crawling or swimming in that it does not rely on any obvious external organ or change in cell shape and it occurs only in the presence of a substrate. Gliding in filamentous cyanobacteria appears to be powered by a "slime jet" mechanism, in which the cells extrude a gel that expands quickly as it hydrates providing a propulsion force, although some
unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...
cyanobacteria use
type IV pili A pilus (Latin for 'hair'; plural: ''pili'') is a hair-like appendage found on the surface of many bacteria and archaea. The terms ''pilus'' and '' fimbria'' (Latin for 'fringe'; plural: ''fimbriae'') can be used interchangeably, although some r ...
for gliding. Individual cells in a
trichome Trichomes (); ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a pla ...
have two sets of pores for extruding slime. Each set is organized in a ring at the cell septae and extrudes slime at an acute angle. The sets extrude slime in opposite directions and so only one set is likely to be activated during gliding. An alternative hypothesis is that the cells use contractive elements that produce undulations running over the surface inside the slime tube like an earthworm. The trichomes rotate in a spiral fashion, the angle of which corresponds with the pitch angle of Castenholz's contractile trichomes. The cells appear to coordinate their gliding direction by an electrical potential that establishes polarity in the trichomes, and thus establishes a "head" and the "tail". Trichomes usually reverse their polarity randomly with an average period on the order of minutes to hours. Many species also form a semi-rigid sheath that is left behind as a hollow tube as the trichome moves forward. When the trichome reverses direction, it can move back into the sheath or break out.
Oscillatoria ''Oscillatoria'' is a genus of filamentous cyanobacterium which is often found in freshwater environments, such as hot springs, and appears blue-green. Its name refers to the oscillating motion of its filaments as they slide against each other ...
is a genus of filamentous cyanobacterium named after the oscillation in its movement. Filaments in colonies slide back and forth against each other until the whole mass is reoriented to its light source. ''Oscillatoria'' is mainly blue-green or brown-green and is commonly found in watering-troughs. It reproduces by fragmentation forming long filaments of cells which can break into fragments called
hormogonia Hormogonia are motile filaments of cells formed by some cyanobacteria in the order Nostocales and Stigonematales. They are formed during vegetative reproduction in unicellular, filamentous cyanobacteria, and some may contain heterocysts and akin ...
. The hormogonia can then grow into new, longer filaments.


Häder's cyanograph experiment

In 1987, Häder demonstrated that
trichome Trichomes (); ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a pla ...
s can position themselves quite precisely within their environment through photomovement. In Häder's cyanograph experiment a photographic negative is projected onto a Petri dish containing a culture of '' Phormidium uncinatum''. After a few hours, the trichomes move away from the darker areas onto the lighter areas, forming a photographic positive on the culture. The experiment demonstrates that photomovement is effective not just for discrete light traps, but for minutely patterned, continuously differentiated light fields as well.


See also

*
Bacterial cellular morphologies Introduction The morphology and arrangement of bacteria are often a key factor in identifying their species. Their direct examination under the light microscope enables the classification of these Bacteria and Archaea . Generally, the basic m ...
* Colonial morphology


References

{{reflist Cyanobacteria