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52-400: Calycomonas Paulinella is a genus of at least eleven species including both freshwater and marine amoeboids . Like many members of euglyphids it is covered by rows of siliceous scales, and use filose pseudopods to crawl over the substrate of the benthic zone . Its most famous members are the three photosynthetic species P. chromatophora , P. micropora and P. longichromatophora ,

104-407: A cyanobiont . The resulting organelle is a photosynthetic plastid that is often referred to as a 'cyanelle' or chromatophore, and it represents the only known primary endosymbiosis event of photosynthetic cyanobacteria (other than the origin of chloroplast ), although primary endosymbiosis with a non-photosynthetic cyanobacterial symbiont have occurred in the diatom family Rhopalodiaceae and

156-406: A lab setting under constant light and water conditions to assess photosynthesis, UVAC and pigmentation production. Moss gametophytes of red and green varieties were exposed to light and consistent watering for a period of two weeks. Following the growth observation, cell wall pigments were extracted from the moss specimens. These extracts were tested using UV–Vis spectrophotometry which uses light from

208-424: A mouth or cytostome , and there is no fixed place on the cell at which phagocytosis normally occurs. Some amoebae also feed by pinocytosis , imbibing dissolved nutrients through vesicles formed within the cell membrane. The size of amoeboid cells and species is extremely variable. The marine amoeboid Massisteria voersi is just 2.3 to 3 micrometres in diameter, within the size range of many bacteria. At

260-531: A novel form of non-photochemical quenching. Another unique, albeit poorly-understood, cyanobacterial strategy involves the IsiA chlorophyll-binding protein , which can aggregate with carotenoids and form rings around the PSI reaction center complexes to aid in photoprotective energy dissipation. Some other cyanobacterial strategies may involve state-transitions of the phycobilisome antenna complex , photoreduction of water with

312-527: A particular risk of forming reactive oxygen species . Therefore, a diverse suite of mechanisms has developed in photosynthetic organisms to mitigate these potential threats, which become exacerbated under high irradiance, fluctuating light conditions, in adverse environmental conditions such as cold or drought, and while experiencing nutrient deficiencies which cause an imbalance between energetic sinks and sources. In eukaryotic phototrophs, these mechanisms include non-photochemical quenching mechanisms such as

364-513: A secondary loss of the amoeboid phase. In his scheme, the Sarcodina were divided into the more primitive Eosarcodina (with the phyla Reticulosa and Mycetozoa) and the more derived Neosarcodina (with the phyla Amoebozoa for lobose amoebae and Rhizopoda for filose amoebae). Shortly after, phylogenetic analyses disproved this hypothesis, as non-amoeboid zooflagellates and amoeboflagellates were found to be completely intermingled with amoebae. With

416-428: A series of molecular phylogenetic analyses confirmed that Sarcodina was not a monophyletic group, and that amoebae evolved from flagellate ancestors. The protozoologist Thomas Cavalier-Smith proposed that the ancestor of most eukaryotes was an amoeboflagellate much like modern heteroloboseans , which in turn gave rise to a paraphyletic Sarcodina from which other groups (e.g., alveolates, animals, plants) evolved by

468-453: A significantly inhibited photoprotection response. Although not yet fully understood, photoprotection is an essential function of plants. Photoprotection of the human skin is achieved by extremely efficient internal conversion of DNA, proteins and melanin. Internal conversion is a photochemical process that converts the energy of the UV photon into small, harmless amounts of heat. If the energy of

520-421: A variety of secondary metabolites beneficial for their survival and protection from excess light. These secondary metabolites that provide plants with protection are commonly used in human sunscreen and pharmaceutical drugs to supplement the inadequate light protection that is innate to human skin cells. Various pigments and compounds can be employed by plants as a form of UV photoprotection as well. Pigmentation

572-505: A very slow growth rate and sensitivity to light, divide every 6–7 days, and prefer low light conditions, probably as a protection against oxidative stress and other light related stress as it doesn't have the same degree of photoprotection mechanisms found in organisms with a photosynthetic apparatus of Archaeplastid origin, which has a much longer evolutionary history. The nuclear genes of P. chromatophora (those regions not affected by endosymbiotic gene transfer) are most closely related to

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624-558: Is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopods . Amoebae do not form a single taxonomic group ; instead, they are found in every major lineage of eukaryotic organisms. Amoeboid cells occur not only among the protozoa , but also in fungi , algae , and animals . Microbiologists often use the terms "amoeboid" and "amoeba" interchangeably for any organism that exhibits amoeboid movement . In older classification systems, most amoebae were placed in

676-411: Is essential to understand why these reactions are important. Due to a steady rise in global temperatures in recent years, many plants have become more susceptible to light damage. Many factors including soil nutrient richness, ambient temperature fluctuation and water availability all impact the photoprotection process in plants. Plants exposed to high light intensity coupled with water deficits displayed

728-513: Is one method employed by a variety of plants as a form of photoprotection. For example, in Antarctica, native mosses of green color can be found naturally shaded by rocks or other physical barriers while red colored mosses of the same species are likely to be found in wind and sun exposed locations. This variation in color is due to light intensity. Photoreceptors in mosses, phytochromes (red wavelengths) and phototropins (blue wavelengths), assist in

780-453: Is the ciliate Pseudoblepharisma tenue , which in addition to a photosynthetic symbiont that is a captured green algae, also has a photosynthetic prokaryote as a symbiont; a purple bacterium with a reduced genome, instead of a cyanobacterium. The chromatophore genome has gone through a reduction, and is now just one third the size of the genome of its closest free living relatives, but still 10-fold larger than most plastid genomes. Some of

832-675: Is transferred across the amoeba's cell membrane by osmosis . Without a contractile vacuole, the cell would fill with excess water and, eventually, burst. Marine amoebae do not usually possess a contractile vacuole because the concentration of solutes within the cell are in balance with the tonicity of the surrounding water. The food sources of amoebae vary. Some amoebae are predatory and live by consuming bacteria and other protists . Some are detritivores and eat dead organic material. Amoebae typically ingest their food by phagocytosis , extending pseudopods to encircle and engulf live prey or particles of scavenged material. Amoeboid cells do not have

884-787: The Acanthamoeba genome . These genes included Spo11 , Mre11 , Rad50 , Rad51 , Rad52 , Mnd1, Dmc1 , Msh and Mlh . This finding suggests that the ‘'Acanthamoeba'’ are capable of some form of meiosis and may be able to undergo sexual reproduction. The meiosis-specific recombinase , Dmc1 , is required for efficient meiotic homologous recombination , and Dmc1 is expressed in Entamoeba histolytica . The purified Dmc1 from E. histolytica forms presynaptic filaments and catalyses ATP -dependent homologous DNA pairing and DNA strand exchange over at least several thousand base pairs . The DNA pairing and strand exchange reactions are enhanced by

936-516: The Radiolaria and Heliozoa , have stiff, needle-like, radiating axopodia (actinopoda) supported from within by bundles of microtubules . Free-living amoebae may be " testate " (enclosed within a hard shell), or "naked" (also known as gymnamoebae , lacking any hard covering). The shells of testate amoebae may be composed of various substances, including calcium , silica , chitin , or agglutinations of found materials like small grains of sand and

988-559: The class or subphylum Sarcodina, a grouping of single-celled organisms that possess pseudopods or move by protoplasmic flow. However, molecular phylogenetic studies have shown that Sarcodina is not a monophyletic group whose members share common descent . Consequently, amoeboid organisms are no longer classified together in one group. The best known amoeboid protists are Chaos carolinense and Amoeba proteus , both of which have been widely cultivated and studied in classrooms and laboratories. Other well known species include

1040-817: The eukaryotic family tree, these results suggest that meiosis was present early in eukaryotic evolution. Furthermore, these findings are consistent with the proposal of Lahr et al. that the majority of amoeboid lineages are anciently sexual. Some amoebae can infect other organisms pathogenically , causing disease: Amoeba have been found to harvest and grow the bacteria implicated in plague . Amoebae can likewise play host to microscopic organisms that are pathogenic to people and help in spreading such microbes. Bacterial pathogens (for example, Legionella ) can oppose absorption of food when devoured by amoebae. The currently generally utilized and best-explored amoebae that host other organisms are Acanthamoeba castellanii and Dictyostelium discoideum. Microorganisms that can overcome

1092-598: The excavates , opisthokonts , stramenopiles and minor clades. The following cladogram shows the sparse positions of amoeboid groups (in bold), based on molecular phylogenetic analyses: Stramenopiles alveolates Rhizaria haptophytes Centroplasthelida plants , etc. euglenids , etc. Heterolobosea CRuMs (incl. Rigifilida ) Amoebozoa Breviatea apusomonads Nucleariids Fungi Photoprotection In organisms that perform oxygenic photosynthesis , excess light may lead to photoinhibition , or photoinactivation of

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1144-406: The frustules of diatoms . To regulate osmotic pressure , most freshwater amoebae have a contractile vacuole which expels excess water from the cell. This organelle is necessary because freshwater has a lower concentration of solutes (such as salt) than the amoeba's own internal fluids ( cytosol ). Because the surrounding water is hypotonic with respect to the contents of the cell, water

1196-401: The heterotrophic P. ovalis . P. ovalis is a marine heterotrophic species of Paulinella that has been shown to eat cyanobacteria and bacteria. P. ovalis also have at least two cyanobacterial-like genes, which were probably integrated into their genome through horizontal gene transfer from its cyanobacterial prey. Similar genes could have made the photosynthetic species pre-equipped to accept

1248-567: The plasma membrane that surrounds the cell. The appearance and internal structure of pseudopods are used to distinguish groups of amoebae from one another. Amoebozoan species, such as those in the genus Amoeba , typically have bulbous (lobose) pseudopods, rounded at the ends and roughly tubular in cross-section. Cercozoan amoeboids, such as Euglypha and Gromia , have slender, thread-like (filose) pseudopods. Foraminifera emit fine, branching pseudopods that merge with one another to form net-like (reticulose) structures. Some groups, such as

1300-418: The reaction centers , a process that does not necessarily involve chemical damage. When photosynthetic antenna pigments such as chlorophyll are excited by light absorption, unproductive reactions may occur by charge transfer to molecules with unpaired electrons. Because oxygenic phototrophs generate O 2 as a byproduct from the photocatalyzed splitting of water (H 2 O) , photosynthetic organisms have

1352-764: The xanthophyll cycle , biochemical pathways which serve as "relief valves", structural rearrangements of the complexes in the photosynthetic apparatus, and use of antioxidant molecules. Higher plants sometimes employ strategies such as reorientation of leaf axes to minimize incident light striking the surface. Mechanisms may also act on a longer time-scale, such as up-regulation of stress response proteins or down-regulation of pigment biosynthesis, although these processes are better characterized as "photoacclimatization" processes. Cyanobacteria possess some unique strategies for photoprotection which have not been identified in plants nor in algae. For example, most cyanobacteria possess an Orange Carotenoid Protein (OCP), which serves as

1404-529: The 20th century. For convenience, all amoebae were grouped as Sarcodina and generally divided into morphological categories , on the basis of the form and structure of their pseudopods . Amoebae with pseudopods supported by regular arrays of microtubules (such as the freshwater Heliozoa and marine Radiolaria ) were classified as Actinopoda , whereas those with unsupported pseudopods were classified as Rhizopoda . The Rhizopods were further subdivided into lobose, filose, plasmodial and reticulose, according to

1456-450: The Austrian zoologist Ludwig Karl Schmarda used "sarcode" as the conceptual basis for his division Sarcodea, a phylum -level group made up of "unstable, changeable" organisms with bodies largely composed of "sarcode". Later workers, including the influential taxonomist Otto Bütschli , amended this group to create the class Sarcodina, a taxon that remained in wide use throughout most of

1508-583: The European Union and United States, afamelanotide is indicated for the prevention of phototoxicity in adults with erythropoietic protoporphyria. Afamelanotide is also being investigated as a method of photoprotection from in the treatment of polymorphous light eruption , actinic keratosis and squamous cell carcinoma (a form of skin cancer ). The cosmetic industry claims that the UV filter acts as an "artificial melanin". But those artificial substances used in sunscreens do not efficiently dissipate

1560-509: The Flavodiiron proteins, and futile cycling of CO 2 . It is widely known that plants need light to survive, grow and reproduce. It is often assumed that more light is always beneficial; however, excess light can actually be harmful for some species of plants. Just as animals require a fine balance of resources, plants require a specific balance of light intensity and wavelength for optimal growth (this can vary from plant to plant). Optimizing

1612-413: The UV and visible spectrum to create an image depicting light absorbance. UVACs are typically found in the cytoplasm of the cell; however, when exposed to high-intensity light, UVACs are transported into the cell wall. It was found that mosses with higher concentrations of red pigments and UVACs located in the cell walls, rather than intracellularly, performed better in higher intensity light. Color change in

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1664-457: The UV photon were not transformed into heat, then it would lead to the generation of free radicals or other harmful reactive chemical species (e.g. singlet oxygen, or hydroxyl radical). In DNA this photoprotective mechanism evolved four billion years ago at the dawn of life. The purpose of this extremely efficient photoprotective mechanism is to prevent direct DNA damage and indirect DNA damage . The ultrafast internal conversion of DNA reduces

1716-406: The ability to shift chloroplasts within the cell farther from the light source thus decreasing the harm done by superfluous light. Similarly, plants are able to produce enzymes that are essential to photoprotection such as Anthocyanin synthase. Plants deficient in photoprotection enzymes are much more sensitive to light damage than plants with functioning photoprotection enzymes. Also, plants produce

1768-671: The addition of many flagellates to Rhizopoda and the removal of some amoebae, the name was rejected in favour of a new name Cercozoa . As such, both names Rhizopoda and Sarcodina were finally abandoned as formal taxa, but they remained useful as descriptive terms for amoebae. The phylum Amoebozoa was conserved, as it still primarily included amoeboid organisms, and now included the Mycetozoa. Today, amoebae are dispersed among many high-level taxonomic groups. The majority of traditional sarcodines are placed in two eukaryote supergroups : Amoebozoa and Rhizaria . The rest have been distributed among

1820-464: The algae Braarudosphaera bigelowii . The endosymbiotic event happened about 90–140 million years ago when an α-cyanobacterium (rather than a β-cyanobacterium which the plastids in Archaeplastida originates from), who diverged about 500 million years ago from the ancestors of its sister clade that consist of the living members of the cyanobacteria genera Prochlorococcus and Synechococcus ,

1872-476: The chromatophore. The presence of extant heterotrophic lineages makes Paulinella a valuable model for unravelling early stages of primary endosymbiosis event and studying the post symbiotic genome evolution of both the plastid and the host. Amoeboid An amoeba ( / ə ˈ m iː b ə / ; less commonly spelled ameba or amœba ; pl. : amoebas (less commonly, amebas ) or amoebae ( amebae ) / ə ˈ m iː b i / ), often called an amoeboid ,

1924-560: The common species now known as Amoeba proteus . The term "Proteus animalcule" remained in use throughout the 18th and 19th centuries, as an informal name for any large, free-living amoeboid. In 1822, the genus Amiba (from the Greek ἀμοιβή amoibe , meaning "change") was erected by the French naturalist Bory de Saint-Vincent . Bory's contemporary, C. G. Ehrenberg , adopted the genus in his own classification of microscopic creatures, but changed

1976-471: The defenses of one-celled organisms can shelter and multiply inside them, where they are shielded from unfriendly outside conditions by their hosts. The earliest record of an amoeboid organism was produced in 1755 by August Johann Rösel von Rosenhof , who named his discovery "Der Kleine Proteus" ("the Little Proteus"). Rösel's illustrations show an unidentifiable freshwater amoeba, similar in appearance to

2028-430: The eukaryotic meiosis-specific recombination accessory factor (heterodimer) Hop2-Mnd1. These processes are central to meiotic recombination, suggesting that E. histolytica undergoes meiosis. Studies of Entamoeba invadens found that, during the conversion from the tetraploid uninucleate trophozoite to the tetranucleate cyst, homologous recombination is enhanced. Expression of genes with functions related to

2080-489: The excited state lifetime of DNA to only a few femtoseconds (10 s)—this way the excited DNA does not have enough time to react with other molecules. For melanin this mechanism has developed later in the course of evolution. Melanin is such an efficient photoprotective substance that it dissipates more than 99.9% of the absorbed UV radiation as heat. This means that less than 0.1% of the excited melanin molecules will undergo harmful chemical reactions or produce free radicals. In

2132-505: The first two being freshwater forms and the third a marine form, which have recently (in evolutionary terms) taken on a cyanobacterium as an endosymbiont . As a result they are no longer able to perform phagocytosis like their non-photosynthetic relatives. P. chromatophora was discovered in sediments of the river Rhine on Christmas Eve 1894 by German biologist Robert Lauterborn , who named it Paulinella after his stepmother Pauline. The event to permanent endosymbiosis probably occurred with

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2184-480: The genes have been lost, others have migrated to the amoeba's nucleus through endosymbiotic gene transfer. It is estimated that 0.3-0.8% of Paulinellas genes were derived from its endosymbiont, in addition to a small amount of genes from other organisms. Other genes have degenerated due to Muller's ratchet – accumulations of harmful mutations due to genetic isolation, and have probably been replaced with genes from other microbes through horizontal gene transfer . Some of

2236-553: The genes the nucleus received from the chromatophore were multiplied many times over through a "copy-paste" mechanism called retrotransposition , enabling them to function more efficiently and making them more tolerant against toxic compounds associated with photosynthesis. This changed the metabolism of the amoeba so much that it could no longer feed on microbes like its ancestors, and it became completely dependent on its endosymbiont, which in turn has lost so many genes it can no longer survive outside its host cell. Paulinella show both

2288-510: The major steps of meiotic recombination also increase during encystations. These findings in E. invadens , combined with evidence from studies of E. histolytica indicate the presence of meiosis in the Entamoeba . Dictyostelium discoideum in the supergroup Amoebozoa can undergo mating and sexual reproduction including meiosis when food is scarce. Since the Amoebozoa diverged early from

2340-407: The morphology of their pseudopods. During the 1980s, taxonomists reached the following classification, based exclusively on morphological comparisons: Archezoa Percolozoa (Heterolobosea)   other excavates Eosarcodina Neosarcodina Apusozoa → Choanozoa → Animals , Fungi Actinopoda Alveolata → Plants , Chromista In the final decades of the 20th century,

2392-457: The mosses was found not to be due to chloroplast movement within the cell. It was found that UVACs and red pigments function as long-term photoprotection in Antarctic mosses. Therefore, in response to high-intensity light stress, the production of UVACs and red pigmentation is up-regulated. Knowing that plants are able to differentially respond to varying concentrations and intensities of light, it

2444-540: The other extreme, the shells of deep-sea xenophyophores can attain 20 cm in diameter. Most of the free-living freshwater amoebae commonly found in pond water , ditches, and lakes are microscopic , but some species, such as the so-called "giant amoebae" Pelomyxa palustris and Chaos carolinense , can be large enough to see with the naked eye. Recent evidence indicates that several Amoebozoa lineages undergo meiosis . Orthologs of genes employed in meiosis of sexual eukaryotes have recently been identified in

2496-540: The process of photosynthesis is essential for survival when environmental conditions are ideal and acclimation when environmental conditions are severe. When exposed to high light intensity, a plant reacts to mitigate the harmful effects of excess light. To best protect themselves from excess light, plants employ a multitude of methods to minimize harm inflicted by excess light. A variety of photoreceptors are used by plants to detect light intensity, direction and duration. In response to excess light, some photoreceptors have

2548-498: The regulation of pigmentation. To better understand this phenomenon, Waterman et al. conducted an experiment to analyze the photoprotective qualities of UVACs (Ultraviolet Absorbing Compounds) and red pigmentation in antarctic mosses. Moss specimens of species Ceratodon purpureus, Bryum pseudotriquetrum and Schistidium antarctici were collected from an island region in East Antarctica . All specimens were then grown and observed in

2600-440: The so-called "brain-eating amoeba" Naegleria fowleri , the intestinal parasite Entamoeba histolytica , which causes amoebic dysentery , and the multicellular "social amoeba" or slime mould Dictyostelium discoideum . Amoeba do not have cell walls, which allows for free movement. Amoeba move and feed by using pseudopods, which are bulges of cytoplasm formed by the coordinated action of actin microfilaments pushing out

2652-427: The spelling to Amoeba . In 1841, Félix Dujardin coined the term " sarcode " (from Greek σάρξ sarx , "flesh," and εἶδος eidos , "form") for the "thick, glutinous, homogeneous substance" which fills protozoan cell bodies. Although the term originally referred to the protoplasm of any protozoan, it soon came to be used in a restricted sense to designate the gelatinous contents of amoeboid cells. Thirty years later,

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2704-559: Was permanently established within the amoeba. It is estimated the last common ancestor of extant photosynthetic species lived about 60 million years ago. This is striking because the chloroplasts of all other known photosynthetic eukaryotes derive ultimately from a single cyanobacterium endosymbiont, which was taken in about 1.6 billion years ago by an ancestral archaeplastidan (and subsequently adopted into other eukaryote groups through secondary endosymbiosis events, and later tertiary and quaternary endosymbiosis, etc). The only exception

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