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79-470: It has been estimated that there are 1.386 billion cubic kilometres (333 million cubic miles) of water on Earth. This includes water in gaseous, liquid and frozen forms as soil moisture, groundwater and permafrost in the Earth's crust (to a depth of 2 km); oceans and seas , lakes , rivers and streams , wetlands , glaciers , ice and snow cover on Earth's surface; vapour, droplets and crystals in

158-484: A mass of 1000  kg , or one tonne . At 0 °C, the freezing point of water, a cubic metre of water has slightly less mass, 999.972 kilograms. A cubic metre is sometimes abbreviated to m^3 , M3 , m**3 , cum , m3 , CBM , cbm when superscript characters or markup cannot be used (e.g. in some typewritten documents and postings in Usenet newsgroups). The "cubic metre" symbol

237-433: A 2021 study on the cyanobacterium Synechocystis . These use a set of genes that regulate the production and export of sulphated polysaccharides , chains of sugar molecules modified with sulphate groups that can often be found in marine algae and animal tissue. Many bacteria generate extracellular polysaccharides, but sulphated ones have only been seen in cyanobacteria. In Synechocystis these sulphated polysaccharide help

316-417: A cyanobacterial species that does so is Microcoleus vaginatus . M. vaginatus stabilizes soil using a polysaccharide sheath that binds to sand particles and absorbs water. M. vaginatus also makes a significant contribution to the cohesion of biological soil crust . Some of these organisms contribute significantly to global ecology and the oxygen cycle . The tiny marine cyanobacterium Prochlorococcus

395-458: A fact that may be responsible for their evolutionary and ecological success. The water-oxidizing photosynthesis is accomplished by coupling the activity of photosystem (PS) II and I ( Z-scheme ). In contrast to green sulfur bacteria which only use one photosystem, the use of water as an electron donor is energetically demanding, requiring two photosystems. Attached to the thylakoid membrane, phycobilisomes act as light-harvesting antennae for

474-411: A key role in developmental processes, such as akinete and heterocyst differentiation, as well as strategy for population survival. Cyanophages are viruses that infect cyanobacteria. Cyanophages can be found in both freshwater and marine environments. Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins. The size of

553-552: A process where the energy of light is used to synthesize organic compounds from carbon dioxide. Because they are aquatic organisms, they typically employ several strategies which are collectively known as a "CO 2 concentrating mechanism" to aid in the acquisition of inorganic carbon (CO 2 or bicarbonate ). Among the more specific strategies is the widespread prevalence of the bacterial microcompartments known as carboxysomes , which co-operate with active transporters of CO 2 and bicarbonate, in order to accumulate bicarbonate into

632-442: A proposed model of microbial distribution, spatial organization, carbon and O 2 cycling in clumps and adjacent areas. (a) Clumps contain denser cyanobacterial filaments and heterotrophic microbes. The initial differences in density depend on cyanobacterial motility and can be established over short timescales. Darker blue color outside of the clump indicates higher oxygen concentrations in areas adjacent to clumps. Oxic media increase

711-412: A range of toxins known as cyanotoxins that can cause harmful health effects in humans and animals. Cyanobacteria are a very large and diverse phylum of photosynthetic prokaryotes . They are defined by their unique combination of pigments and their ability to perform oxygenic photosynthesis . They often live in colonial aggregates that can take on a multitude of forms. Of particular interest are

790-559: 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. However, reports on cell death of marine and freshwater cyanobacteria indicate this process has major implications for the ecology of microbial communities/ Different forms of cell demise have been observed in cyanobacteria under several stressful conditions, and cell death has been suggested to play

869-492: A serious threat to aquatic environments and public health, and are increasing in frequency and magnitude globally. Cyanobacteria are ubiquitous in marine environments and play important roles as primary producers . They are part of the marine phytoplankton , which currently contributes almost half of the Earth's total primary production. About 25% of the global marine primary production is contributed by cyanobacteria. Within

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948-500: A symbiotic relationship with plants or lichen -forming fungi (as in the lichen genus Peltigera ). Cyanobacteria are globally widespread photosynthetic prokaryotes and are major contributors to global biogeochemical cycles . They are the only oxygenic photosynthetic prokaryotes, and prosper in diverse and extreme habitats. They are among the oldest organisms on Earth with fossil records dating back at least 2.1 billion years. Since then, cyanobacteria have been essential players in

1027-419: A waving motion; the filament oscillates back and forth. In water columns, some cyanobacteria float by forming gas vesicles , as in archaea . These vesicles are not organelles as such. They are not bounded by lipid membranes , but by a protein sheath. Some cyanobacteria can fix atmospheric nitrogen in anaerobic conditions by means of specialized cells called heterocysts . Heterocysts may also form under

1106-408: A weaker cell in a filament, called a necridium. Some filamentous species can differentiate into several different cell types: Each individual cell (each single cyanobacterium) typically has a thick, gelatinous cell wall . They lack flagella , but hormogonia of some species can move about by gliding along surfaces. Many of the multicellular filamentous forms of Oscillatoria are capable of

1185-578: A wide range of cyanobacteria and are key regulators of the cyanobacterial populations in aquatic environments, and may aid in the prevention of cyanobacterial blooms in freshwater and marine ecosystems. These blooms can pose a danger to humans and other animals, particularly in eutrophic freshwater lakes. Infection by these viruses is highly prevalent in cells belonging to Synechococcus spp. in marine environments, where up to 5% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles. The first cyanophage, LPP-1 ,

1264-458: Is m . It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes , was the stère , still sometimes used for dry measure (for instance, in reference to wood ). Another alternative name, no longer widely used, was the kilolitre . A cubic metre of pure water at the temperature of maximum density (3.98 °C) and standard atmospheric pressure (101.325 kPa) has

1343-417: Is a way for the cells to maximize the use of available light for photosynthesis. A few genera lack phycobilisomes and have chlorophyll b instead ( Prochloron , Prochlorococcus , Prochlorothrix ). These were originally grouped together as the prochlorophytes or chloroxybacteria, but appear to have developed in several different lines of cyanobacteria. For this reason, they are now considered as part of

1422-422: Is about 1.4 × 10 tonnes , which is about 0.023% of Earth's total mass. At any given time, about 2 × 10 tonnes of this is in the form of water vapor in the Earth's atmosphere (for practical purposes, 1 cubic metre of water weighs 1 tonne). Approximately 71% of Earth's surface, an area of some 361 million square kilometres (139.5 million square miles), is covered by ocean . The average salinity of Earth's oceans

1501-568: Is about 35 grams of salt per kilogram of sea water (3.5%). According to Merriam Webster, the word hydrosphere was brought into English in 1887, translating the German term hydrosphäre , introduced by Eduard Suess . The water cycle refers to the transfer of water from one state or reservoir to another. Reservoirs include atmospheric moisture (snow, rain and clouds), streams, oceans, rivers, lakes, groundwater , subterranean aquifers , polar ice caps and saturated soil. Solar energy , in

1580-565: Is encoded by Unicode at code point U+33A5 ㎥ SQUARE M CUBED . Cyanobacteria As of 2014 the taxonomy was under revision Cyanobacteria ( / s aɪ ˌ æ n oʊ b æ k ˈ t ɪər i . ə / ), also called Cyanobacteriota or Cyanophyta , are a phylum of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis . The name "cyanobacteria" (from Ancient Greek κύανος ( kúanos )  'blue') refers to their bluish green ( cyan ) color, which forms

1659-728: Is favoured in ponds and lakes where waters are calm and have little turbulent mixing. Their lifecycles are disrupted when the water naturally or artificially mixes from churning currents caused by the flowing water of streams or the churning water of fountains. For this reason blooms of cyanobacteria seldom occur in rivers unless the water is flowing slowly. Growth is also favoured at higher temperatures which enable Microcystis species to outcompete diatoms and green algae , and potentially allow development of toxins. Based on environmental trends, models and observations suggest cyanobacteria will likely increase their dominance in aquatic environments. This can lead to serious consequences, particularly

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1738-487: Is known regarding the nature (e.g., genetic diversity, host or cyanobiont specificity, and cyanobiont seasonality) of the symbiosis involved, particularly in relation to dinoflagellate host. Some cyanobacteria – even single-celled ones – show striking collective behaviours and form colonies (or blooms ) that can float on water and have important ecological roles. For instance, billions of years ago, communities of marine Paleoproterozoic cyanobacteria could have helped create

1817-485: Is later used to make amino acids and proteins. Marine picocyanobacteria ( Prochlorococcus and Synechococcus ) numerically dominate most phytoplankton assemblages in modern oceans, contributing importantly to primary productivity. 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 . Amongst

1896-445: Is neither created nor destroyed, it only migrates. There is no evidence that water vapor escapes into space." Every year the turnover of water on Earth involves 577,000 km of water. This is water that evaporates from the oceanic surface (502,800 km) and from land (74,200 km). The same amount of water falls as atmospheric precipitation, 458,000 km on the ocean and 119,000 km on land. The difference between precipitation and evaporation from

1975-419: Is possibly the most plentiful genus on Earth: a single millilitre of surface seawater can contain 100,000 cells of this genus or more. Worldwide there are estimated to be several octillion (10 , a billion billion billion) individuals. Prochlorococcus is ubiquitous between latitudes 40°N and 40°S, and dominates in the oligotrophic (nutrient-poor) regions of the oceans. The bacterium accounts for about 20% of

2054-469: Is the residual (after use) per capita quantity of fresh water." Fresh water resources are unevenly distributed in terms of space and time and can go from floods to water shortages within months in the same area. In 1998, 76% of the total population had a specific water availability of less than 5.0 thousand m per year per capita. Already by 1998, 35% of the global population suffered "very low or catastrophically low water supplies," and Shiklomanov predicted that

2133-546: Is the term used by hydrologists in reference to the three processes together, transpiration, sublimation and evaporation. Marq de Villiers has described the hydrosphere as a closed system in which water exists. The hydrosphere is intricate, complex, interdependent, all-pervading, stable, and "seems purpose-built for regulating life." De Villiers claimed that, "On earth, the total amount of water has almost certainly not changed since geological times: what we had then we still have. Water can be polluted, abused, and misused but it

2212-449: The biosphere as we know it by burying carbon compounds and allowing the initial build-up of oxygen in the atmosphere. On the other hand, toxic cyanobacterial blooms are an increasing issue for society, as their toxins can be harmful to animals. 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 shown in

2291-486: The black band disease ). Cyanobacteria can be found in almost every terrestrial and aquatic habitat  – oceans , fresh water , damp soil, temporarily moistened rocks in deserts , bare rock and soil, and even Antarctic rocks. They can occur as planktonic cells or form phototrophic biofilms . They are found inside stones and shells (in endolithic ecosystems ). A few are endosymbionts in lichens , plants, various protists , or sponges and provide energy for

2370-629: The early Earth 's anoxic, weakly reducing prebiotic atmosphere , into an oxidizing one with free gaseous oxygen (which previously would have been immediately removed by various surface reductants ), resulting in the Great Oxidation Event and the " rusting of the Earth " during the early Proterozoic , dramatically changing the composition of life forms on Earth. The subsequent adaptation of early single-celled organisms to survive in oxygenous environments likely had led to endosymbiosis between anaerobes and aerobes , and hence

2449-448: The filamentous species , which often dominate the upper layers of microbial mats found in extreme environments such as hot springs , hypersaline water , deserts and the polar regions, but are also widely distributed in more mundane environments as well. They are evolutionarily optimized for environmental conditions of low oxygen. Some species are nitrogen-fixing and live in a wide variety of moist soils and water, either freely or in

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2528-501: The host . Some live in the fur of sloths , providing a form of camouflage . Aquatic cyanobacteria are known for their extensive and highly visible blooms that can form in both freshwater and marine environments. The blooms can have the appearance of blue-green paint or scum. These blooms can be toxic , and frequently lead to the closure of recreational waters when spotted. Marine bacteriophages are significant parasites of unicellular marine cyanobacteria. Cyanobacterial growth

2607-464: The Earth's ecosystems. Planktonic cyanobacteria are a fundamental component of marine food webs and are major contributors to global carbon and nitrogen fluxes . 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 . Nowadays, cyanobacterial blooms pose

2686-602: The accumulation of particulate organic carbon (cells, sheaths and heterotrophic organisms) in clumps. It has been unclear why and how cyanobacteria form communities. Aggregation must divert resources away from the core business of making more cyanobacteria, as it generally involves the production of copious quantities of extracellular material. In addition, cells in the centre of dense aggregates can also suffer from both shading and shortage of nutrients. So, what advantage does this communal life bring for cyanobacteria? New insights into how cyanobacteria form blooms have come from

2765-490: The activities of ancient cyanobacteria. They are often found as symbionts with a number of other groups of organisms such as fungi (lichens), corals , pteridophytes ( Azolla ), angiosperms ( Gunnera ), etc. The carbon metabolism of cyanobacteria include the incomplete Krebs cycle , the pentose phosphate pathway , and glycolysis . There are some groups capable of heterotrophic growth, while others are parasitic , causing diseases in invertebrates or algae (e.g.,

2844-606: The air; and part of living plants, animals and unicellular organisms of the biosphere. Saltwater accounts for 97.5% of this amount, whereas fresh water accounts for only 2.5%. Of this fresh water, 68.9% is in the form of ice and permanent snow cover in the Arctic, the Antarctic and mountain glaciers ; 30.8% is in the form of fresh groundwater; and only 0.3% of the fresh water on Earth is in easily accessible lakes, reservoirs and river systems. The total mass of Earth's hydrosphere

2923-480: The appropriate environmental conditions (anoxic) when fixed nitrogen is scarce. Heterocyst-forming species are specialized for nitrogen fixation and are able to fix nitrogen gas into ammonia ( NH 3 ), nitrites ( NO − 2 ) or nitrates ( NO − 3 ), which can be absorbed by plants and converted to protein and nucleic acids (atmospheric nitrogen is not bioavailable to plants, except for those having endosymbiotic nitrogen-fixing bacteria , especially

3002-460: The aquifer will run dry. Additionally, only one third of rivers are free-flowing due to the extensive use of dams, levees, hydropower , and habitat degradation. Excessive water use has also caused intermittent streams to become more dry, which is dangerous because they are extremely important for water purification and habitat. Other ways humans impact the hydrosphere include eutrophication , acid rain , and ocean acidification . Humans also rely on

3081-439: The atmosphere. As the Earth cooled the water vapor in the atmosphere condensed and fell as rain. The atmosphere cooled further as atmospheric carbon dioxide dissolved into the rain water. In turn, this further caused water vapor to condense and fall as rain. This rain water filled the depressions on the Earth's surface and formed the oceans. It is estimated that this occurred about 4000 million years ago. The first life forms began in

3160-448: The basis of cyanobacteria's informal common name , blue-green algae , although as prokaryotes they are not scientifically classified as algae . Cyanobacteria are probably the most numerous taxon to have ever existed on Earth and the first organisms known to have produced oxygen , having appeared in the middle Archean eon and apparently originated in a freshwater or terrestrial environment . Their photopigments can absorb

3239-432: The clump from the overlying medium and is also produced within the clump by respiration. In oxic solutions, high O 2 concentrations reduce the efficiency of CO 2 fixation and result in the excretion of glycolate. Under these conditions, clumping can be beneficial to cyanobacteria if it stimulates the retention of carbon and the assimilation of inorganic carbon by cyanobacteria within clumps. This effect appears to promote

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3318-918: The contamination of sources of drinking water . Researchers including Linda Lawton at Robert Gordon University , have developed techniques to study these. 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. Consequences may also lie within fisheries and waste management practices. Anthropogenic eutrophication , rising temperatures, vertical stratification and increased atmospheric carbon dioxide are contributors to cyanobacteria increasing dominance of aquatic ecosystems. Cyanobacteria have been found to play an important role in terrestrial habitats and organism communities. It has been widely reported that cyanobacteria soil crusts help to stabilize soil to prevent erosion and retain water. An example of

3397-434: The cyanobacteria, only a few lineages colonized the open ocean: Crocosphaera and relatives, cyanobacterium UCYN-A , Trichodesmium , as well as Prochlorococcus and Synechococcus . 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, by converting nitrogen gas into ammonium, which

3476-509: The cyanobacterial group. In general, photosynthesis in cyanobacteria uses water as an electron donor and produces oxygen as a byproduct, though some may also use hydrogen sulfide a process which occurs among other photosynthetic bacteria such as the purple sulfur bacteria . Carbon dioxide is reduced to form carbohydrates via the Calvin cycle . The large amounts of oxygen in the atmosphere are considered to have been first created by

3555-462: The cyanobacterium form buoyant aggregates by trapping oxygen bubbles in the slimy web of cells and polysaccharides. Previous studies on Synechocystis have shown type IV pili , which decorate the surface of cyanobacteria, also play a role in forming blooms. These retractable and adhesive protein fibres are important for motility, adhesion to substrates and DNA uptake. The formation of blooms may require both type IV pili and Synechan – for example,

3634-497: The cytoplasm of the cell. Carboxysomes are icosahedral structures composed of hexameric shell proteins that assemble into cage-like structures that can be several hundreds of nanometres in diameter. It is believed that these structures tether the CO 2 -fixing enzyme, RuBisCO , to the interior of the shell, as well as the enzyme carbonic anhydrase , using metabolic channeling to enhance the local CO 2 concentrations and thus increase

3713-432: The diagram on the right, bacteria can stay in suspension as individual cells, adhere collectively to surfaces to form biofilms, passively sediment, or flocculate to form suspended aggregates. Cyanobacteria are able to produce sulphated polysaccharides (yellow haze surrounding clumps of cells) that enable them to form floating aggregates. In 2021, Maeda et al. discovered that oxygen produced by cyanobacteria becomes trapped in

3792-464: The efficiency of the RuBisCO enzyme. In contrast to purple bacteria and other bacteria performing anoxygenic photosynthesis , thylakoid membranes of cyanobacteria are not continuous with the plasma membrane but are separate compartments. The photosynthetic machinery is embedded in the thylakoid membranes, with phycobilisomes acting as light-harvesting antennae attached to the membrane, giving

3871-930: The evolution of eukaryotes during the Paleoproterozoic . Cyanobacteria use photosynthetic pigments such as various forms of chlorophyll , carotenoids , phycobilins to convert the photonic energy in sunlight to chemical energy . Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes . These are flattened sacs called thylakoids where photosynthesis is performed. Photoautotrophic eukaryotes such as red algae , green algae and plants perform photosynthesis in chlorophyllic organelles that are thought to have their ancestry in cyanobacteria, acquired long ago via endosymbiosis. These endosymbiont cyanobacteria in eukaryotes then evolved and differentiated into specialized organelles such as chloroplasts , chromoplasts , etioplasts , and leucoplasts , collectively known as plastids . Sericytochromatia,

3950-443: The family Fabaceae , among others). Free-living cyanobacteria are present in the water of rice paddies , and cyanobacteria can be found growing as epiphytes on the surfaces of the green alga, Chara , where they may fix nitrogen. Cyanobacteria such as Anabaena (a symbiont of the aquatic fern Azolla ) can provide rice plantations with biofertilizer . Cyanobacteria use the energy of sunlight to drive photosynthesis ,

4029-477: The filamentous forms, Trichodesmium are free-living and form aggregates. However, filamentous heterocyst-forming cyanobacteria (e.g., Richelia , Calothrix ) are found in association with diatoms such as Hemiaulus , Rhizosolenia and Chaetoceros . Marine cyanobacteria include the smallest known photosynthetic organisms. The smallest of all, Prochlorococcus , is just 0.5 to 0.8 micrometres across. In terms of numbers of individuals, Prochlorococcus

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4108-408: The first signs of multicellularity. Many cyanobacteria form motile filaments of cells, called hormogonia , 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

4187-403: The form of heat and light ( insolation ), and gravity cause the transfer from one state to another over periods from hours to thousands of years. Most evaporation comes from the oceans and is returned to the earth as snow or rain. Sublimation refers to evaporation from snow and ice. Transpiration refers to the expiration of water through the minute pores or stomata of trees. Evapotranspiration

4266-481: The green pigmentation observed (with wavelengths from 450 nm to 660 nm) in most cyanobacteria. While most of the high-energy electrons derived from water are used by the cyanobacterial cells for their own needs, a fraction of these electrons may be donated to the external environment via electrogenic activity. Respiration in cyanobacteria can occur in the thylakoid membrane alongside photosynthesis, with their photosynthetic electron transport sharing

4345-417: The head and tail vary among species of cyanophages. Cyanophages, like other bacteriophages , rely on Brownian motion to collide with bacteria, and then use receptor binding proteins to recognize cell surface proteins, which leads to adherence. Viruses with contractile tails then rely on receptors found on their tails to recognize highly conserved proteins on the surface of the host cell. Cyanophages infect

4424-681: The health of the hydrosphere. It is used for water supply, navigation, fishing, agriculture, energy, and recreation. Cubic kilometer The cubic metre (in Commonwealth English and international spelling as used by the International Bureau of Weights and Measures ) or cubic meter (in American English ) is the unit of volume in the International System of Units (SI). Its symbol

4503-462: The hydrosphere and natural processes within. Humans are withdrawing water from aquifers and diverting rivers at an unprecedented rate. The Ogallala Aquifer is used for agriculture in the United States; if the aquifer goes dry, more than $ 20 billion worth of food and fiber will vanish from the world's markets. The aquifer is being depleted so much faster than it is replenished that, eventually,

4582-417: The land surface (119,000 − 74,200 = 44,800 km/year) represents the total runoff of the Earth's rivers (42,700 km/year) and direct groundwater runoff to the ocean (2100 km/year). These are the principal sources of fresh water to support life necessities and man's economic activities. Water is a basic necessity of life. Since two thirds of the Earth is covered by water, the Earth is also called the blue planet and

4661-544: The most abundant photosynthetic organisms on Earth, accounting for a quarter of all carbon fixed in marine ecosystems. In contrast to free-living marine cyanobacteria, some cyanobionts are known to be responsible for nitrogen fixation rather than carbon fixation in the host. However, the physiological functions of most cyanobionts remain unknown. Cyanobionts have been found in numerous protist groups, including dinoflagellates , tintinnids , radiolarians , amoebae , diatoms , and haptophytes . Among these cyanobionts, little

4740-453: The most extreme niches such as hot springs, salt works, and hypersaline bays. Photoautotrophic , oxygen-producing cyanobacteria created the conditions in the planet's early atmosphere that directed the evolution of aerobic metabolism and eukaryotic photosynthesis. Cyanobacteria fulfill vital ecological functions in the world's oceans, being important contributors to global carbon and nitrogen budgets." – Stewart and Falconer Some cyanobacteria,

4819-406: The network of polysaccharides and cells, enabling the microorganisms to form buoyant blooms. It is thought that specific protein fibres known as pili (represented as lines radiating from the cells) may act as an additional way to link cells to each other or onto surfaces. Some cyanobacteria also use sophisticated intracellular gas vesicles as floatation aids. The diagram on the left above shows

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4898-414: The oceans. These organisms did not breathe oxygen. Later, when cyanobacteria evolved, the process of conversion of carbon dioxide into food and oxygen began. As a result, Earth's atmosphere has a distinctly different composition from that of other planets and allowed for life to evolve on Earth . Human activity has had an impact on the water cycle. Infrastructure, like dams, have a clear, direct impact on

4977-418: The oxygen in the Earth's atmosphere. Cyanobacteria are variable in morphology, ranging from unicellular and filamentous to colonial forms . Filamentous forms exhibit functional cell differentiation such as heterocysts (for nitrogen fixation), akinetes (resting stage cells), and hormogonia (reproductive, motile filaments). These, together with the intercellular connections they possess, are considered

5056-716: The photosystems. The phycobilisome components ( phycobiliproteins ) are responsible for the blue-green pigmentation of most cyanobacteria. The variations on this theme are due mainly to carotenoids and phycoerythrins that give the cells their red-brownish coloration. In some cyanobacteria, the color of light influences the composition of the phycobilisomes. In green light, the cells accumulate more phycoerythrin, which absorbs green light, whereas in red light they produce more phycocyanin which absorbs red. Thus, these bacteria can change from brick-red to bright blue-green depending on whether they are exposed to green light or to red light. This process of "complementary chromatic adaptation"

5135-443: 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. 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. Type IV pili on their own could also control

5214-413: The pili may help to export the polysaccharide outside the cell. Indeed, the activity of these protein fibres may be connected to the production of extracellular polysaccharides in filamentous cyanobacteria. A more obvious answer would be that pili help to build the aggregates by binding the cells with each other or with the extracellular polysaccharide. As with other kinds of bacteria, certain components of

5293-481: The position of marine cyanobacteria in the water column by regulating viscous drag. Extracellular polysaccharide appears to be a multipurpose asset for cyanobacteria, from floatation device to food storage, defence mechanism and mobility aid. One of the most critical processes determining cyanobacterial eco-physiology is cellular death . Evidence supports the existence of controlled cellular demise in cyanobacteria, and various forms of cell death have been described as

5372-478: The proposed name of the paraphyletic and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria. The cyanobacteria Synechocystis and Cyanothece are important model organisms with potential applications in biotechnology for bioethanol production, food colorings, as a source of human and animal food, dietary supplements and raw materials. Cyanobacteria produce

5451-468: The red- and blue-spectrum frequencies of sunlight (thus reflecting a greenish color) to split water molecules into hydrogen ions and oxygen. The hydrogen ions are used to react with carbon dioxide to produce complex organic compounds such as carbohydrates (a process known as carbon fixation ), and the oxygen is released as a byproduct . By continuously producing and releasing oxygen over billions of years, cyanobacteria are thought to have converted

5530-427: The reversal frequencies of any filaments that begin to leave the clumps, thereby reducing the net migration away from the clump. This enables the persistence of the initial clumps over short timescales; (b) Spatial coupling between photosynthesis and respiration in clumps. Oxygen produced by cyanobacteria diffuses into the overlying medium or is used for aerobic respiration. Dissolved inorganic carbon (DIC) diffuses into

5609-448: The root surface within a restricted zone by Nostoc . 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. Cyanobacteria, mostly pico-sized Synechococcus and Prochlorococcus , are ubiquitously distributed and are

5688-514: The roots of wheat and cotton plants. Calothrix sp. has also been found on the root system of wheat. Monocots , such as wheat and rice, have been colonised by Nostoc spp., In 1991, Ganther and others isolated diverse heterocystous nitrogen-fixing cyanobacteria, including Nostoc , Anabaena and Cylindrospermum , from plant root and soil. Assessment of wheat seedling roots revealed two types of association patterns: loose colonization of root hair by Anabaena and tight colonization of

5767-415: The same compartment as the components of respiratory electron transport. While the goal of photosynthesis is to store energy by building carbohydrates from CO 2 , respiration is the reverse of this, with carbohydrates turned back into CO 2 accompanying energy release. Cyanobacteria appear to separate these two processes with their plasma membrane containing only components of the respiratory chain, while

5846-441: The situation would deteriorate in the twenty-first century with "most of the Earth's population living under the conditions of low or catastrophically low water supply" by 2025. Only 2.5% of the water in the hydrosphere is fresh water and only 0.25% of that water is accessible for our use. The activities of modern humans have drastic effects on the hydrosphere. For instance, water diversion, human development, and pollution all affect

5925-429: The so-called cyanobionts (cyanobacterial symbionts), have a symbiotic relationship with other organisms, both unicellular and multicellular. As illustrated on the right, there are many examples of cyanobacteria interacting symbiotically with land plants . Cyanobacteria can enter the plant through the stomata and colonize the intercellular space, forming loops and intracellular coils. Anabaena spp. colonize

6004-473: The thylakoid membrane hosts an interlinked respiratory and photosynthetic electron transport chain. Cyanobacteria use electrons from succinate dehydrogenase rather than from NADPH for respiration. Cyanobacteria only respire during the night (or in the dark) because the facilities used for electron transport are used in reverse for photosynthesis while in the light. Many cyanobacteria are able to reduce nitrogen and carbon dioxide under aerobic conditions,

6083-612: The water cycle by blocking and redirecting water pathways. Human caused pollution has changed the biogeochemical cycles of some water systems, and climate change has significantly altered weather patterns. Water withdrawals have exponentially increased because of agriculture, state and domestic use, and infrastructure. According to Igor A. Shiklomanov , it takes 2500 years for the complete recharge and replenishment of oceanic waters, 10,000 years for permafrost and ice, 1500 years for deep groundwater and mountainous glaciers, 17 years in lakes, and 16 days in rivers. "Specific water availability

6162-506: The watery planet. The hydrosphere plays an important role in the existence of the atmosphere in its present form. Oceans are important in this regard. When the Earth was formed it had only a very thin atmosphere rich in hydrogen and helium similar to the present atmosphere of Mercury. Later the gases hydrogen and helium were expelled from the atmosphere. The gases and water vapor released as the Earth cooled became its present atmosphere. Other gases and water vapor released by volcanoes also entered

6241-500: Was discovered in 1986 and accounts for more than half of the photosynthesis of the open ocean. Circadian rhythms were once thought to only exist in eukaryotic cells but many cyanobacteria display a bacterial circadian rhythm . "Cyanobacteria are arguably the most successful group of microorganisms on earth. 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

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