Organisms Such as Amoebas and Paramecium Can Be Found in What Type Ofenvironments

Microorganisms (Microbes), Role of☆

T. Fenchel , in Reference Module in Life Sciences, 2017

Unicellular Eukaryotes (Protists)

Protists are known to include many unrelated eukaryotic groups. Eukaryote cells differ from prokaryotes in possessing a cytoskeleton and membrane-covered organelles, among which mitochondria and chloroplasts are recognized equally beingness descendants of endosymbiotic aerobic bacteria belonging to the α group of proteobacteria and to cyanobacteria, respectively. Protists accept a much greater size range than bacteria; the smallest gratis-living species measure approximately iii µm and the largest may attain sizes of several centimeters.

Phagocytosis is probably a primary property of eukaryotic cells and nearly extant species depend on particulate food (mainly bacteria or other protists). Many groups take acquired chloroplasts; this has apparently happened independently in unlike taxa and examples of "chloroplasts," which stand for intermediate stages between an endosymbiont, and an organelle are known. Many species have secondarily lost chloroplasts and thus the power of photosynthesis. Inside many groups of phototrophs the power of phagocytosis has been retained (mixotrophs, constitute, for case, amid chrysomonads and dinoflagellates); in other groups (eg, diatoms and green algae) phagocytosis has been irreversibly lost. A few species (some ciliates and foraminiferans) are capable of retaining chloroplasts from their prey cells; the chloroplasts remain functional for some days and this is exploited by the "host." Many heterotrophic protists harbor endosymbiotic phototrophs. Very few protists subsist on dissolved organic affair; in nigh habitats they would be inferior competitors to bacteria simply due to their larger size. The majority of protists are aerobes; a few specialized protists, nevertheless, are obligate anaerobes depending on a fermentative metabolism. Tolerance to extreme conditions is limited relative to that of some bacteria, but otherwise protists are omnipresent; primarily they are the principal consumers of bacteria in all types of environments and phototroph protists are largely responsible for primary production in aquatic habitats (Fenchel, 1987).

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Ecology of Rare Microorganisms

Pierre E. Galand , Ramiro Logares , in Encyclopedia of Microbiology (Fourth Edition), 2019

What About Protists?

Protists are key components of microbial communities (Caron et al., 2009; Worden et al., 2015), yet, for historical reasons, they have been overlooked in customs ecology studies every bit well as in studies focusing on rare taxa. Protists feature primal differences with prokaryotes in terms of cellular construction, feeding habits, diversity of metabolisms, growth rates and behaviour (Massana and Logares, 2013; Keeling and Del Campo, 2017). Therefore, understanding rare prokaryotes does non imply that we empathize rare protists. The available studies thus far indicate that protistan communities feature a large number of rare taxa that establish a "rare biosphere" (Caron and Countway, 2009; Logares et al., 2015). Even though there are no figures as in prokaryotes, we suspect that with the current amount of sequencing we are only sampling the tip of the iceberg of the protistan rare biosphere. Interestingly, Massana and Logares (2013) proposed that the size of the rare protistan biosphere could exist smaller than in its prokaryotic counterparts, given that survival mechanisms in protists could be less adult than in prokaryotes. Some other reason is that the "delights of a diluted life" (Pedrós-Alió, 2006b), may non be so obvious for protists. Some picoeukaryotes may non exist able to escape predation even after reducing their cell size to the minimum (Massana and Logares, 2013). Furthermore, most small protists are naked, the lack of a rigid cell-wall may limit their opportunities for dormancy. In addition, several protist species may appoint in sex, which represents a process that helps maintaining the cohesiveness of eukaryotic species. If the chances of finding a sexual partner get extremely depression, as it could happen in the rare biosphere, so the advantages of rarity would be reduced amongst protists. I of import divergence between the latter groups is that while prokaryotes seem to enter into a dormant state hands and and so establish a seed-depository financial institution, this behaviour does not seem to be that mutual in aquatic protists (Massana and Logares, 2013; Logares et al., 2015). Thus, it follows that rare protists are likely metabolically active (Logares et al., 2015). This has been supported past a study in lakes that institute a potent coupling between the full number of protists detected (rDNA fraction) and the active protists (rRNA fraction) (Jones and Lennon, 2010b). In dissimilarity, the total and active bacterial communities analysed in the latter study were decoupled. For protists, like results to those obtained past Jones and Lennon (2010b) were obtained by Logares et al. (2014b) in a study of marine-littoral communities from Europe. There, researchers did not observe large deviations in the full and active communities, pointing to metabolic activity in abundant equally well as in rare taxa. In sum, aquatic protistan communities also feature a rare biosphere, yet, whether its size is equal or smaller than that of prokaryotes is a matter of debate. What seems to be clear is that protists do not grade extensive seed-banks as prokaryotes, and therefore, communities experiencing repeatable changes (e.thou., seasonal) probably reconstitute previous states by recruiting metabolically active, yet low-affluence, taxa.

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Mitochondrial Genome, Development

B. Franz Lang , ... Gertraud Burger , in Encyclopedia of Biological Chemistry, 2004

Protist mtDNAs

Protists are a heterogeneous group of eukaryotes that are negatively divers every bit not belonging to the animal, fungal, or found kingdoms. Based on ultrastructural characteristics, several dozen protist phyla are distinguished, but the evolutionary relationships among these phyla are mostly contentious. Many protist mitochondrial genomes are more bacteria-like, and encode a substantially larger set of genes than those of animals and fungi (Table I). Withal, mtDNA of several parasitic protists exhibit novel and puzzling features. For instance, the linear mtDNA (6   kbp) of the malaria parasite Plasmodium falciparum carries only v genes. Its rRNAs are encoded by many small gene pieces. Another oddity is plant in trypanosomatid parasites, whose mtDNA consists of a network of thousands of concatenated minicircles and a few dozen maxicircles. The RNAs transcribed from maxicircle genes undergo massive RNA editing through nucleotide insertions and deletions to generate translatable mRNAs.

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Protists: Flagellates and Amoebae☆,***

Robert W. Sanders , in Reference Module in Earth Systems and Ecology Sciences, 2021

Distribution

In the pelagic zone (water cavalcade)

Protists are able to position themselves in the h2o column through several mechanisms including production of gas or lipid vacuoles noted previously for the testate amoebae Difflugia. All the same, swimming with flagella is the most common way that motile algae and heterotrophic flagellates position themselves in response to a variety of gradients in a stratified water cavalcade. Light requirements compel phototrophs to maintain themselves in the euphotic zone where at that place is plenty light to support photosynthesis at to the lowest degree some of the time, but many phototrophs will swim deeper to avoid bright light. Motile photosynthetic organisms with algal symbionts, such as some dinoflagellates (and ciliates), are known to migrate toward the surface in the morning and into deeper, potentially nutrient-richer layers, after in the twenty-four hours.

Most heterotrophic protists tend to reply to other environmental parameters such as food abundance or oxygen. The greatest numbers of bacterivorous protists are associated with areas of college bacterial production. In contrast, algivorous protists volition tend to accumulate in layers where light and nutrient levels are all-time for their photosynthetic prey. Some costless-living heterotrophs, including the flagellates Hexamita and Trepomonas, are common in areas of sediments (see beneath) and the hypolimnetic layers of eutrophic waters where loftier organic enrichment leads to low oxygen or anoxia. The amoeba-flagellate Mastigamoeba lacks mitochondria and so its distribution is limited to anoxic water.

Aggregates of detritus occur in the water column (as well as the benthos) and these will often have higher abundances of bacteria. Every bit noted above, increases in bacterial prey lead to higher abundances of heterotrophic protists on these microhabitats relative to the surrounding water—peculiarly in oligotrophic systems (Caron, 1991). Occurrence of "benthic" protists, such as the flagellate Bodo, in the h2o column may exist due to association with these aggregates. Another distinct habitat, the air-h2o interface, also can be enriched with protists that employ the surface as a substrate. Both naked and testate amoebae, such as Arcella, and some flagellates (due east.one thousand., Codonosiga) tin can hang beneath or motion atop the water's surface feeding on bacteria or phototrophs growing there.

There tends to be stiff seasonal changes in the abundance and species composition of aquatic protists. Phototrophic species frequently decline in winter and increase over again with the longer days and greater low-cal intensity in the leap. Bacterial activity increases with autotroph activeness since the photosynthetic organisms release dissolved organic matter that supplies substrate for leaner. Heterotrophic protist populations then will increment in response to affluence of algal and bacterial prey. Temperature too tends to be positively related to protistan population growth rates, so the low photosynthesis and low growth rates of winter lead to minimum abundances of flagellates and amoebae, while their productivity tends to increment in warmer seasons.

Sediments and difficult substrates

The benthic habitat in both lake and stream systems tends to accumulate organic affair and detritus, which offers both a food source and a habitat for benthic protists. Attached and motile protists can occur in high numbers on and in the sediments. Attached heterotrophic organisms typically create a current to bring suspended food from the water (e.g., Bicosoeca, Fig. 1), or allow fabric to fall or swim into specialized feeding appendages (east.g., heliozoan axopodia). Phototrophic species can form mats or biofilms, especially on hard substrates that often have high abundances of cyanobacteria with or without protistan phototrophs. Motile protists movement on and through these biofilms, and also at the surface and within the sediment. In sediments with relatively high organic matter content, gradients set up with sediment depth including modify in oxygen, redox potential, pH and other chemicals. As noted for the plankton to a higher place, species that prefer oxic, microaerophylic, or anoxic environments will move to advisable depths in the sediment or volition even leave the sediment and move into the water column. The sediments are a source of the anaerobic protists that announced in the h2o column when anoxic hypolimnia develop, typically during summer, in stratified lakes.

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Microbial Diversity

Paul 5. Dunlap , in Encyclopedia of Biodiversity (Second Edition), 2001

Protista

The Protista is a large complex grouping of mostly unicellular eukaryotic organisms. They are morphologically diverse and can be found in well-nigh terrestrial, aquatic, and marine habitats as complimentary-living forms and as parasites of other protists, of fungi, and of plants and animals. With their nutritional modes restricted primarily to osmo- and phago-heterotrophy and phototrophy, protists are metabolically much less diverse than Leaner and Archaea. Along with various independent amoeboid groups, major groupings include the Alveolates, equanimous of ciliates (e.m., Paramecium), dinoflagellates (e.g., Alexandrium), and apicomplexans (e.g., Plasmodium), and the Stramenopiles, composed of the brown and golden-brown algae, diatoms, chrysophytes, oomycetes, and distinct groups of slime molds, among other groups. Cryptophytes, Rhodophytes, and Haptophytes are other major groupings of protists. Forth with these groups are the diplomonads, trichomonads, microsporidia, amoeba-flagelates, and euglenoids (Figure 6).

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Interactions Between Fungi and Other Microbes

Lynne Boddy , in The Fungi (Third Edition), 2016

Interactions Between Fungi and Protists

Protists and fungi are likely to encounter each other ofttimes in soil, aquatic ecosystems and in the guts of ruminants, but interactions between them have received little attention. In that location is certainly evidence of protists feeding on fungi. Some testate amoebae (e.g. Geococcus vulgaris), spike to the walls of fungal spores and hyphae and suck out the contents. There is also show that protists may reduce ectomycorrhizal colonisation of roots and reduce the amount of mycorrhizal mycelium in the mycorrhizosphere. Considerable interactions between fungi and protists occurs in the rumen (pp. 329–330) – ciliate protozoa ingest Neocallimastigomycota zoospores, and their predatory activity tin can reduce overall cellulolytic action and change the fermentation products formed.

Plasmodia of myxomycetes have been shown to consume fungi in lab culture, the susceptibility of the latter varying between species of myxomycetes and fungi. Plasmodia volition feed on mycelia mats that emerge from wood nether moist weather condition, and on resupinate fungal fruit bodies. The fungi in decay columns extending for many centimetres through wood can be completely devoured by plasmodia. For instance, Badhamia utricularis has been seen to consume the ascomycete Xylaria hypoxylon, and Comatricha nigra consumes the basidiomycete Stereum hirsutum. Myxomycetes can be prevalent in forest; in one study myxoflagellates emerged from most 50% of fallen dead angiosperm branches sampled, having been active vegetatively or having emerged rapidly from microcysts; Stemonitis fusca was particularly common.

The tables are turned, however, by Dactylella passalopaga, amid others, which produces bulbous outgrowths which trap testate amoeba. Several Zoopagales (zygomycete) adhere to amoeba and feed on them. Also, some isolates of Heteroconium chaetospira (a dark septate root endophyte; pp. 238–239) can control clubroot illness of Brassicacae, caused by the soil-borne protozoan Plasmodiophora brassicae. The fungus infects root epidermal cells, but the mechanism of disease control is unclear.

Some fungi colonise the fruit bodies of myxomycetes. Hyphae penetrate the spore masses and kill the spores. Other fungi (e.m. the ascomycete Gliocladium anthology), parasitize the calcium-rich fruit bodies of the Physarales; Nectriopsis violacea is even more specific, only colonising species of Fuligo. Others are specific to non-calcareous myxomycetes, yet others colonise a wide host range, Nectria exigua being recorded on all of the major myxomycete groups. In lab culture on agar, the hemiascomycete yeast, Dipodascus utricularis, is able to live in the slime trail of Badhamia utricularis. If the yeast is ingested it is not digested and lives parasitically, multiplying within the myxomycete plasmodium.

From a medical mycology viewpoint, interactions between amoebae and fungi which are saprotrophic in the natural environment, just which tin can cause systemic infection in humans (pp. 303–309) and other mammals, are of detail interest. The yeast form of the pathogens Blastomyces dermatidis, Cryptococcus neoformans, Histoplasma capsulatum, and Sporothrix schenckii are ingested by amoebae, but inhibit amoebal growth or kill them. Outcomes of interactions, however, vary depending on the combination of species interacting. For instance, growth of Candida albicans is enhanced past the amoeba Hartmannella vermiformis but killed by Acanthamoeba castellanii. Similarly, spores of Aspergillus fumigatus (p. 306) are ingested by amoebae; the spores can germinate inside the cytoplasm and the mucus is released to the environment. These interactions betwixt amoebae and yeasts and spores are similar to those with homo macrophages, and the interaction of these saprotrophic fungi with amoebae in the natural environment over evolutionary time has been described as a 'preparation ground' for overcoming the macrophage defences of vertebrates.

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Cells and Organisms

David P. Clark , ... Michelle R. McGehee , in Molecular Biological science (3rd Edition), 2019

Kingdom Protista was a potpourri pot of organisms that did non fit into one of the other three kingdoms. Equally such, the kingdom was artificially various. In 2005, Adl et al. proposed a new, higher level of classification for eukaryotes that most specifically impacted the protists. The new classification scheme was based upon both structural and molecular data. In this approach, half dozen clusters or supergroups were proposed: Opisthokonta, Amoebozoa, Excavata, Rhizaria, Archaeplastida, and Chromalveolata. In 2012, a bit more than rearrangement took place that combined stramenopiles and alveolates (two groups from within Chromalveolata) plus Rhizaria into one supergroup designated as SAR. The three existing kingdoms (plants, animals, and fungi), still fit within this scheme although Opisthokonta and Amoebozoa have been merged. For example, Kingdoms Animalia and Fungi are within Supergroup Unikonta along with the flagellated ancestors. Kingdom Plantae is contained entirely inside Supergroup Archaeplastida, which as well includes the cherry algae and green algae. The other supergroups include many unicellular eukaryotes that are often simply referred to every bit protists but the Kingdom Protista has mostly been rearranged in an attempt to ameliorate understand and communicate the evolutionary relationships ( Fig. i.xiv). At that place is still much debate on how to adapt the eukaryotes with the above supergroup scheme garnering some support, particularly for Unikonta. Equally new data is acquired, these arrangements will likely continue to evolve.

Figure 1.14. Arrangement of Supergroups

The currently accustomed interpretation of the relationship of members of Domain Eukarya. A few representative groups of organisms are added for reference.

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Mixotrophy Amid Freshwater and Marine Protists

Per J. Hansen , ... Kevin J. Flynn , in Encyclopedia of Microbiology (Quaternary Edition), 2019

Prey Selection

Well-nigh mixotrophic protists are idea to feed on a wide range of prey and the nutrition usually includes bacteria and/or other protists, but it may in some cases also include copepods and mollusc larvae. In contrast, some protists are quite selective and rely on specific species of prey. For case, the ciliate Mesodinium rubrum utilizes a specific clade of cryptophytes, which are incorporated into the jail cell body of M. rubrum allowing the ciliate to rely on photosynthesis every bit its major carbon source. In plough, M. rubrum is specifically consumed by Dinophysis spp. (dinoflagellate) in gild to acquire the cryptophyte chloroplasts from the ciliate.

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Physiological Adaptations of Protists

Michael Levandowsky , in Cell Physiology Source Volume (Quaternary Edition), 2012

IIIB The Contractile Vacuole

Protists without prison cell walls that live in hypotonic media (freshwater species) take contractile vacuoles (CV), which periodically excrete fluid. In the best-studied case, the ciliate Paramecium, this consists of a key vacuole, a surrounding circuitous of ampullae and a network, or spongiome, of tubules (Fig. 49.3). Certain tubules in this complex are decorated with peg-like elements that are vacuolar-type proton pumps. These are found in both the cellular slime mold Dictyostelium and the ciliate Paramecium (Heuser et al., 1993; Allen, 1997).

Effigy 49.3. Contractile vacuole circuitous in Paramecium, showing ampullae (amp), collecting canal (cc), contractile vacuole (cv), pore (pv), spongiomal tubules (sp), fluid segregation organelles (fs) and microtubular ribbons (mtr).

(Adapted with permission from Hausmann and Hülsmann, 1996.)

Excretion occurs through a cycle. During diastole, the vacuole forms and grows by the fusion of smooth-membrane vesicles. During this flow, fluid travels from the spongiome to the CV. In systole, the vacuole membrane fuses with the cell membrane at 1 site to form a pore and the fluid is excreted. As this happens, the vacuole contracts as its membrane fragments and forms vesicles once more. Actin has not been detected virtually the CV and contraction is thought to be due to cellular force per unit area later the appearance of the pore opening to the exterior. At one time it was thought that the connections of the CV to the spongiome were interrupted during systole, preventing backflow. Contempo piece of work, even so, indicates that the connections persist throughout the wheel. The narrowness of the tubular connections presents great resistance, and then that considerable pressure would be required for a rapid backflow during systole.

A major office of the CV is clearly osmoregulation. The cycle ceases in cells placed in a hypertonic medium, resuming after a time when the jail cell adapts and increases internal tonicity. Fluid in the CV is loftier in K⁺ and Na⁺, relative to the cytoplasm, also suggesting a role in maintenance of ionic rest.

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Natural Products Structural Diversity-II Secondary Metabolites: Sources, Structures and Chemic Biological science

Jörn Piel , in Comprehensive Natural Products Two, 2010

two.14.two Protists

Protists are a taxonomically inhomogeneous group of by and large unicellular eukaryotic microorganisms. Dinoflagellates (superphylum Alveolata) are protists and are the about important source of natural products (see Chapter ii.09). ¹ Several species form massive blooms in the ocean, known as red tides, and many are notorious producers of neurotoxins, mainly circuitous polyketides, that may accumulate in nutrient chains. Besides playing important roles as photosynthesizing endosymbionts in corals and other marine invertebrates (run across the post-obit sections), many dinoflagellates are also hosts for leaner, raising questions almost the bodily origin of the toxins. Classical tillage studies and culture-contained approaches, such as fluorescence in situ hybridization (FISH), denaturing gradient gel electrophoresis (DGGE), and 16S ribosomal RNA (rRNA) analysis, revealed a remarkable diversity of taxa and loci of attachment within or outside the eukaryotic jail cell. ^two–6 The majority of the identified strains belonged to the phyla Proteobacteria and Bacteroidetes, but members of Cyanobacteria and Actinobacteria have too been detected. Most studies on symbiotic toxin producers centered on saxitoxin ( 1 ) and related compounds ( Scheme one ), which are paralytic shellfish poisons (PSPs) of nonpolyketidic origin. Several free-living cyanobacteria of the genera Anabaena, ⁷ Lyngbia, ⁸ and Aphanizomenon ⁹ have been discovered that produce saxitoxins, suggesting a bacterial origin in the dinoflagellate. However, reports on the true producer take been contradicting. They include (1) the isolation of a large number of unrelated bacterial PSP producers from Alexandrium spp., ¹⁰ among them an intracellular γ-proteobacterium from surface-sterilized Alexandrium tamarense, ^xi (ii) the driblet of PSP product in dinoflagellates treated with antibacterial agents, ¹² (3) the occurrence of toxin production in axenic dinoflagellate cultures, ¹³ and (4) a Mendelian inheritance scheme of biosynthetic capabilities, suggesting the location of biosynthetic genes on the dinoflagellate genome. ¹⁴ Several scenarios could explicate these discrepancies. It has been pointed out that the methods most ordinarily used for PSP detection, that is, high-performance liquid chromatography (HPLC) and mouse neuroblastoma assay, are non specific plenty and might generate false-positive results. ^15,16 A 2d possibility is that PSP biosynthetic genes are present in dinoflagellates besides as in leaner, either due to horizontal gene transfer or convergent evolution, only that not all strains produce the compounds. Mod techniques such every bit loftier-sensitivity nuclear magnetic resonance (NMR) analysis or the localization of biosynthetic genes will very probable resolve this issue.

Scheme one.

Several researchers have addressed the question whether dinoflagellate polyketides might be of bacterial origin. In immunofluorescence assays, okadaic acid two did non colocalize with bacteria, providing indication for host production (unless metabolites are transported betwixt cells). ¹⁷ In add-on, several lines of show, such as FISH on separated cells ¹⁸ and the generation of reverse-transcript polymerase concatenation reaction (RT-PCR) amplicons from polyadenylated, that is, eukaryotic, RNA, ^nineteen demonstrated that dinoflagellate genomes can harbor polyketide synthase (PKS) genes. In the lite of these results and the uniqueness of dinoflagellate polyketides regarding structure and biosynthesis, ⁱ a host origin is very likely.

A modest number of compounds take been isolated from bacterial cultures obtained from dinoflagellates. In the case of Pfiesteria spp. dinoflagellates, signaling between symbiotic partners has been studied in more item. Members of the Roseobacter clade are attracted to these hosts by using the dinoflagellate-derived substance dimethylsulfoniopropionate ( 3 ) as chemic cue. ^xx The leaner colonize the host, catabolize the compound, and contain a part of the assimilated sulfur into an antibiotic, tropodithietic acrid ( four ). ²¹ In another report, species of Marinobacter that are required for the growth of the flower-erstwhile Gymnodinium catenatum produce the siderophore vibrioferrin ( 5 ), ²² a known natural product showtime reported from pathogenic Vibrio parahemolyticus. ²³ In improver to iron, 5 also binds borate, which is common in marine just not terrestrial environments. 5 is therefore suspected to mediate signaling processes or boron send. A farther example of signaling chemistry is quorum sensing (QS; sensing of the prison cell density within a population) mediated past long-chain acylhomoserine lactones, such as 6 , that have been isolated from the dinoflagellate-associated γ-proteobacterium Dinoroseobacter shibae. ²⁴

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