Planktothrix | |
---|---|
![]() | |
Planktothrix rubescens | |
Scientific classification ![]() | |
Domain: | Bacteria |
Phylum: | Cyanobacteria |
Class: | Cyanophyceae |
Order: | Oscillatoriales |
Family: | Microcoleaceae |
Genus: | Planktothrix Anagnostidis & Komárek, 1988 |
Planktothrix is a diverse genus of filamentous cyanobacteria observed to amass in algal blooms in water ecosystems across the globe. Like all Oscillatoriales, Planktothrix species have no heterocysts and no akinetes. Planktothrix are unique because they have trichomes and contain gas vacuoles unlike typical planktonic organisms. [1] Previously, some species of the taxon were grouped within the genus Oscillatoria , but recent work has defined Planktothrix as its own genus. [2] A tremendous body of work on Planktothrix ecology and physiology has been done by Anthony E. Walsby, and the 55.6 kb microcystin synthetase gene which gives these organisms the ability to synthesize toxins has been sequenced. [3] P. agardhii is an example of a type species of the genus. [4] P. agardhii and P. rubescens are commonly observed in lakes of the Northern Hemisphere where they are known producers of potent hepatotoxins called microcystins. [5]
Both P. agardhii and P. rubescens have the ability to form massive blooms in freshwater lakes and reservoirs. The whole genus has been studied to thrive in various temperate to subtropical water ecosystems in Europe, Asia, Africa and Australia. [6] P. agardhii is commonly found at most latitudes in shallow and turbid lakes where it can tolerate continuous mixing of the water column. [7] P. rubescens is regularly found in clear, deep alpine and pre-alpine lakes that are seasonally stratified. [8] P. agardhii grows in the low light conditions of the metalimnion where it can maximize the absorption of green light with its phycoerythrin pigments. [9] Under the action of wind-induced internal waves, P. rubescens can be moved vertically by several meters following the movements of the metalimnion, which in turn modifies rapidly (within a day) the light conditions experienced by the filaments. [10] This was shown to significantly affect the photosynthesis rate and oxygen production especially in lakes where the dominant organism of the phytoplankton community is P. rubescens such as in Lake Zurich. [10] [11] [12]
The various strains of Planktothrix can be characterized as planktic, benthic, or biphasic based on their lifestyles and at what depth in the water they are found. [6] The various species can not only be differentiated by their preferred habitat type but also by their morphology and pigmentation. [13] For example, the blue green pigmented species P. agardhii possess phycocyanins giving its color. At the same time, outbreaks of P. rubescens are known as the "Burgundy-blood phenomenon" in reference to its reddish pigmentation. [14] Different strains prefer climates ranging from temperate to subtropic. Planktothrix grows by cell division in a single plane to form unbranched structures of average length around 4 μm, but unlike other Oscillatoriales, these trichomes are phototactic. Typically, Planktothrix filaments do not have specialized cells such as akinetes or heterocysts, and do not produce mucilaginous envelopes, except for some rare species but only under stress conditions. [4] Several species possess a constant ratio of their two main photosynthetic pigments, i.e., phycocyanins and phycoerythrins. [4] The production of cyanotoxins is facultative, [4] and strains that do not produce microcystins are commonly found in nature. [8] Apart from microcystins, they can produce several other cyclic peptides including oscillapeptin J. [15] Planktothrix organisms house gas vesicles called protoplasts which play an important role in their buoyancy as the gas within the vesicle is nearly only one tenth the density of water making the organism less dense overall. [13]
The Plantothrix genus emerged as a cyanobacteria observed to form blooms at the surface of freshwater and organisms with the current classification were once categorized under the genus Oscillatoria. [13]
Planktothrix organisms are able to store nitrogen as a co-polymer of aspartate and arginine which allows them to survive even under limited nitrogen supply from the atmosphere. [13] This mechanism is also what allows thick blooms to prosper as the thicker the bloom, deeper Planktothrix are exposed to less light and atmospheric air. The increasing impact of algal blooms has been theorized to be connected to global warming caused by human activity. [16] Harmful algal blooms caused by not only Planktothrix but also other forms of cyanobacteria including Dolichospermum (Anabaena) or Microcystis have correlation to toxic effects for humans leading to devastating impacts to agriculture. [17] [18] Planktothrix have the ability to produce cyanotoxins including microcystins, anatoxins, and saxitoxins. [18]
An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term algae encompasses many types of aquatic photosynthetic organisms, both macroscopic multicellular organisms like seaweed and microscopic unicellular organisms like cyanobacteria. Algal bloom commonly refers to the rapid growth of microscopic unicellular algae, not macroscopic algae. An example of a macroscopic algal bloom is a kelp forest.
Cyanobacteria, also called Cyanobacteriota or Cyanophyta, are a phylum of autotrophic gram-negative bacteria that can obtain biological energy via photosynthesis. The name 'cyanobacteria' refers to their color, which similarly forms the basis of cyanobacteria's common name, blue-green algae, although they are not scientifically classified as algae. They appear to have originated in a freshwater or terrestrial environment.
Microcystins—or cyanoginosins—are a class of toxins produced by certain freshwater cyanobacteria, commonly known as blue-green algae. Over 250 different microcystins have been discovered so far, of which microcystin-LR is the most common. Chemically they are cyclic heptapeptides produced through nonribosomal peptide synthases.
Trichodesmium, also called sea sawdust, is a genus of filamentous cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters. Trichodesmium is a diazotroph; that is, it fixes atmospheric nitrogen into ammonium, a nutrient used by other organisms. Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally. Trichodesmium is the only known diazotroph able to fix nitrogen in daylight under aerobic conditions without the use of heterocysts.
Cyanotoxins are toxins produced by cyanobacteria. Cyanobacteria are found almost everywhere, but particularly in lakes and in the ocean where, under high concentration of phosphorus conditions, they reproduce exponentially to form blooms. Blooming cyanobacteria can produce cyanotoxins in such concentrations that they can poison and even kill animals and humans. Cyanotoxins can also accumulate in other animals such as fish and shellfish, and cause poisonings such as shellfish poisoning.
Aphanizomenon flos-aquae is a brackish and freshwater species of cyanobacteria of the genus Aphanizomenon found around the world, including the Baltic Sea and the Great Lakes.
Anabaena circinalis is a species of Gram-negative, photosynthetic cyanobacteria common to freshwater environments throughout the world. Much of the scientific interest in A. circinalis owes to its production of several potentially harmful cyanotoxins, ranging in potency from irritating to lethal. Under favorable conditions for growth, A. circinalis forms large algae-like blooms, potentially harming the flora and fauna of an area.
Anatoxin-a, also known as Very Fast Death Factor (VFDF), is a secondary, bicyclic amine alkaloid and cyanotoxin with acute neurotoxicity. It was first discovered in the early 1960s in Canada, and was isolated in 1972. The toxin is produced by multiple genera of cyanobacteria and has been reported in North America, South America, Central America, Europe, Africa, Asia, and Oceania. Symptoms of anatoxin-a toxicity include loss of coordination, muscular fasciculations, convulsions and death by respiratory paralysis. Its mode of action is through the nicotinic acetylcholine receptor (nAchR) where it mimics the binding of the receptor's natural ligand, acetylcholine. As such, anatoxin-a has been used for medicinal purposes to investigate diseases characterized by low acetylcholine levels. Due to its high toxicity and potential presence in drinking water, anatoxin-a poses a threat to animals, including humans. While methods for detection and water treatment exist, scientists have called for more research to improve reliability and efficacy. Anatoxin-a is not to be confused with guanitoxin, another potent cyanotoxin that has a similar mechanism of action to that of anatoxin-a and is produced by many of the same cyanobacteria genera, but is structurally unrelated.
Cylindrospermopsin is a cyanotoxin produced by a variety of freshwater cyanobacteria. CYN is a polycyclic uracil derivative containing guanidino and sulfate groups. It is also zwitterionic, making it highly water soluble. CYN is toxic to liver and kidney tissue and is thought to inhibit protein synthesis and to covalently modify DNA and/or RNA. It is not known whether cylindrospermopsin is a carcinogen, but it appears to have no tumour initiating activity in mice.
Aphanizomenon is a genus of cyanobacteria that inhabits freshwater lakes and can cause dense blooms. They are unicellular organisms that consolidate into linear (non-branching) chains called trichomes. Parallel trichomes can then further unite into aggregates called rafts. Cyanobacteria such as Aphanizomenon are known for using photosynthesis to create energy and therefore use sunlight as their energy source. Aphanizomenon bacteria also play a big role in the Nitrogen cycle since they can perform nitrogen fixation. Studies on the species Aphanizomenon flos-aquae have shown that it can regulate buoyancy through light-induced changes in turgor pressure. It is also able to move by means of gliding, though the specific mechanism by which this is possible is not yet known.
Nodularins are potent toxins produced by the cyanobacterium Nodularia spumigena, among others. This aquatic, photosynthetic cyanobacterium forms visible colonies that present as algal blooms in brackish water bodies throughout the world. The late summer blooms of Nodularia spumigena are among the largest cyanobacterial mass occurrences in the world. Cyanobacteria are composed of many toxic substances, most notably of microcystins and nodularins: the two are not easily differentiated. A significant homology of structure and function exists between the two, and microcystins have been studied in greater detail. Because of this, facts from microcystins are often extended to nodularins.
A harmful algal bloom (HAB), or excessive algae growth, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are sometimes defined as only those algal blooms that produce toxins, and sometimes as any algal bloom that can result in severely lower oxygen levels in natural waters, killing organisms in marine or fresh waters. Blooms can last from a few days to many months. After the bloom dies, the microbes that decompose the dead algae use up more of the oxygen, generating a "dead zone" which can cause fish die-offs. When these zones cover a large area for an extended period of time, neither fish nor plants are able to survive. Harmful algal blooms in marine environments are often called "red tides".
Anthony Edward Walsby, BSc(Birm), PhD(Lond), FRS, is the Emeritus Professor of Microbiology at the School of Biological Sciences, University of Bristol.
Microcystis aeruginosa is a species of freshwater cyanobacteria that can form harmful algal blooms of economic and ecological importance. They are the most common toxic cyanobacterial bloom in eutrophic fresh water. Cyanobacteria produce neurotoxins and peptide hepatotoxins, such as microcystin and cyanopeptolin. Microcystis aeruginosa produces numerous congeners of microcystin, with microcystin-LR being the most common. Microcystis blooms have been reported in at least 108 countries, with the production of microcystin noted in at least 79.
Raphidiopsis raciborskii is a freshwater cyanobacterium.
Cyanopeptolins (CPs) are a class of oligopeptides produced by Microcystis and Planktothrix algae strains, and can be neurotoxic. The production of cyanopeptolins occurs through nonribosomal peptides synthases (NRPS).
Gloeotrichia is a large (~2 mm) colonial genus of Cyanobacteria, belonging to the order Nostocales. The name Gloeotrichia is derived from its appearance of filamentous body with mucilage matrix. Found in lakes across the globe, gloeotrichia are notable for the important roles that they play in the nitrogen and phosphorus cycles. Gloeotrichia are also a species of concern for lake managers, as they have been shown to push lakes towards eutrophication and produce deadly toxins.
Trichodesmium thiebautii is a cyanobacteria that is often found in open oceans of tropical and subtropical regions and is known to be a contributor to large oceanic surface blooms. This microbial species is a diazotroph, meaning it fixes nitrogen gas (N2), but it does so without the use of heterocysts. T. thiebautii is able to simultaneously perform oxygenic photosynthesis. T. thiebautii was discovered in 1892 by M.A. Gomont. T. thiebautii are important for nutrient cycling in marine habitats because of their ability to fix N2, a limiting nutrient in ocean ecosystems.
Susanna Wood is a New Zealand scientist whose research focuses on understanding, protecting and restoring New Zealand's freshwater environments. One of her particular areas of expertise is the ecology, toxin production, and impacts of toxic freshwater cyanobacteria in lakes and rivers. Wood is active in advocating for the incorporation of DNA-based tools such as metabarcoding, genomics and metagenomics for characterising and understanding aquatic ecosystems and investigating the climate and anthropogenic drivers of water quality change in New Zealand lakes. She has consulted for government departments and regional authorities and co-leads a nationwide programme Lakes380 that aims to obtain an overview of the health of New Zealand's lakes using paleoenvironmental reconstructions. Wood is a senior scientist at the Cawthron Institute. She has represented New Zealand in cycling.
Aphanizomenon ovalisporum is a filamentous cyanobacteria present in many algal blooms.