L>Summary to Medical ProtozoologyINTRODUCTION TO MEDICAL PROTOZOOLOGYWhat Are Protozoa? Deciphering the Greek roots outcomes in specifying protozoa as "first" (proto) "animals" (zoa). Although molecular phylohereditary researches show that protozoa are among the earliest branching eukaryotes (view phylogenetic tree), such a definition does not carry out a lot descriptive indevelopment. Protozoa are not easily defined bereason they are diverse and also are frequently only distantly concerned each various other. Due to the extreme diversity of the protozoa the only feature prevalent to all protozoa is that they are unicellular eukaryotic micro-organisms. Protozoa possess typical eukaryotic organelles and in basic exhibit the typical functions of other eukaryotic cells. For example, a membrane bound nucleus containing the chromosomes is discovered in all protozoan species. However before, in many protozoan species some of the organelles may be missing, or are morphologically or functionally different from those found in various other eukaryotes. In addition, many type of of the protozoa have organelles that are unique to a specific group of protozoa. Questions one might ask in regards to defining protozoa include: What carry out they look like? How massive are they? Where perform they live? How perform they relocate about? How do they reproduce? Protozoa exhilittle bit a large array of morphologies (click figure for larger image and also description). Tright here is no one shape or morphology which would include a majority of the protozoa. Shapes selection from the amorphous and ever-altering develops of ameba to reasonably rigid creates dictated in part by highly ordered cytoskeleloads or secreted walls or shells. Several protozoan species express photofabricated or other pigments and also for this reason are colored. Many protozoan species exhilittle complex life cycles via multiple stages. Sometimes the various life cycle steras are so disequivalent that they have actually been mistaken for completely different species. Protozoan SizesOrganismSizePlasmodium merozoites 2-5 µm Paramecium 200-500 µm Spirostomum ambiguum3 mmNummulites(fossilized)7-13 cm Protozoa--except for a couple of early american forms--are unicellular, or single-celled, organisms; although, some argue that they are actually "acellular". Therefore, the substantial majority of protozoa are microscopic. However before, they execute exhilittle bit an exceptionally huge variety of sizes. Extant species selection in dimension from m (10-6 meter) to numerous mm. Fossilized Forminiferida of several cm have been identified. (Extinct protozoa can be detected because of a secreted calcium carbonate shell.) Most of the organisms discussed in this course will certainly be 3-50 µm. This small size necessitates the use of a microscope to detect protozoa. An electron microscopic lense is essential for in-depth morphological studies. Protozoa are discovered in moist atmospheres practically anywhere. As a group, the protozoa are extremely adaptable. Individual species, though, generally have certain niches. Like all other organisms, protozoa have to be able to obtain and also metabolize nutrients from their atmosphere (i.e., heterotrophic). Many protozoa ssuggest absorb solutes (i.e., osmotrophy) from their media, while some are scavengers that ingest solid product (i.e., phagotrophy). Predatory protozoa either actively hunt dvery own or passively ambush various other organisms (typically bacteria or various other protozoa). Some protozoa are photoman-made and have the right to capture the power of the sun and also convert it to usable chemical power (i.e., autotrophic or phototrophic). Many kind of protozoa are not restricted to a solitary feeding system and also have the right to make use of combicountries of the over (i.e., mixotrophic).Protozoa deserve to likewise be perceived as free-living or symbiotic. Typically free-living organisms are uncovered in the soil or aqueous atmospheres, whereas symbionts live in cshed association via an additional organism. Symbiosis indicates a physiological dependency of one organism on one more organism and also not just a cshed physical association in between 2 organisms. Usually this dependency is in the create of nutrition. Different develops of symbiosis can be distinguished which reflect the nature of the association in between the 2 organisms (Box). Symbiotic Associations Commensalism Denotes an interaction that is valuable to one organism yet has actually no impact on the other organism. For instance, many kind of protozoa live in the alimentary canal of one more organism without harming it. These commensals are frequently scavengers or predators that make use of the abundance of nutrients or bacterial fauna provided by the organize organism. Mutualism Denotes a distinct form of commensalism in which both organisms derive some benefit and have become dependent on each various other. The classic instance of mutualism is the protozoan Trichonympha uncovered in the gut of termites. Trichonympha, via the assistance of a symbiotic bacteria, digests the hardwood particles (i.e., cellulose) ingested by the termite. Parasitism Denotes a relationship in which one organism (the parasite) benefits at the price of the other organism (the host). Typically this organize cost implies that the parawebsite absorbs macromolecules from the hold and also releases others into the organize. In some instances the parasitism will certainly be overtly harmful to the hold and also referred to as being pathogenic. These pathogenic protozoa are the main focus of this course. Motility and also the Cytoskeleton Modes of MotilityMechanismSubgroupameboid movementamebasflagellaflagellatesciliaciliatesgliding motilitysporozoaThe earliest observations of protozoa listed their motility. This motility led to their classification as "animals", which were distinguiburned from the non-motile "plants". However, motility is not a global function of protozoa and various protozoa make use of different mechanisms for their motion (Table). In truth, protozoa were initially classified based in part on their device of motility (see Taxonomy). Cilia and also flagella are subcellular structures which propel protozoa through a liquid medium. Flagella are lengthy whip-choose frameworks which propel the organism as an outcome of wave-prefer beat which is propagated through their size. Flagellated protozoa commonly have one or a couple of flagella per organism. In comparison, ciliated protozoa are commonly spanned via rows of countless cilia. The beats of these cilia are coordinated and attribute choose oars to propel the organism. Cilia and flagella can also aid in the procurement of food, remanufacturing and also various other attributes. Cilia and also flagella are consisted of of the exact same protein components and also are actually tantamount frameworks. Both are membrane bound filamentous projections from the cell. The filament, known as an axoneme, is written of a collection of parallel microtubules, frequently exhibiting a "9 + 2" arrangement. Movement is developed as soon as the microtubules slide past each other. The pressure which mediates this sliding activity is generated by a protein referred to as dynein. Dyneins are "motor proteins" which transform the chemical power released by ATP hydrolysis into a mechanical power. Microtubules are cytoskeletal aspects which additionally play essential functions in cell form and are a significant component of the mitotic spindle.In comparison to the swimming showed by flagellates and also ciliates, ameba are protozoa that crawl alengthy a solid substratum in a fashion recognized as "ameboid movement". The ameba jobs out a pseudopodium, or false foot, from the cell body. The pseudopodium then attaches to the substratum and also then pulls the rest of the cell body forward. The pressure affiliated in this motion is produced by an additional cytoskeletal system, which is made up of actin and myosin. Actin develops lengthy filaments, also known as microfilaments, and also myosin is a motor protein which moves along the microfilaments in an ATP dependent manner. Muscle contractivity is an additional example of the force generation via actin-myosin cytoskeletal elements. In a mechanistic sense, phagocytosis is a kind of ameboid movement also entailing microfilaments. In this situation the pseudopodia are extfinished to surround the pwrite-up being ingested. Fusion of the pseudopodia with the cell body results in the internalization of the particle within a vacuole. Apicomplexa likewise crawl alengthy a substratum, however by a various system than the ameba. The mechanism of this so-called "gliding motility" is just beginning to be understood and also probably requires both microfilament and also microtubule based cytoskeletal units. Apicomplexa additionally exhibit intracellular develops and intrusion of the host cell also requires this gliding motility. (See also conversation of hold cell intrusion by the malaria parawebsite.)Cellular motility involves pressure generation with either the microtubule-based cytoskeletal facets or the microfilament-based cytoskeletal facets. This is true for protozoa and also various other eukaryotes. The involvement of microtubules and microfilaments in both cell form and also cell activity make these subcellular frameworks more analogous to the musculoskeletal system. ReproductionModes of ReproductionAsexualBinary FissionMultiple FissionsBuddingSexualFusion of GametesConjugationProtozoa, favor all various other organisms, reproduce. The the majority of widespread develop of remanufacturing in protozoa is asex-related binary fission. In various other words, a solitary organism will divide into two equal organisms. A slight change of this binary fission, called budding, is once one of the newly formed cells is smaller than the other. Typically the bigger cell is dubbed the mother and also the smaller sized is the daughter. Some protozoa will certainly form an intracellular bud and essentially provide birth. Another variation of binary fission is a multiple fission or segmentation. In this case, several rounds of nuclear replication occur without cytokinesis. This multinucleated cell will certainly then form multiple progeny all at once.Many protozoa exhilittle bit sex-related reproduction in enhancement to the asexual develops of remanufacturing. This sex-related remanufacturing deserve to involve the manufacturing and also fusion of gametes in procedures equivalent to greater organisms. The Ciliophora undergo a conjugation in which oppowebsite mating types will certainly pair and directly exreadjust genetic material (i.e., DNA). Sometimes sexual reproduction is an obligatory step in the life cycle, whereas in other instances the organism have the right to reproduce asexually via an occasional round of sexual remanufacturing.In summary, protozoa are unicellular eukaryotic microorganisms. However before, the amount of diversity in regards to morphology, size and also life styles exhilittle by protozoa renders it difficult to construct a more exact interpretation. Their lengthy evolutionary background (see phylohereditary tree) accounts for a lot of this diversity. However, protozoa perform exhilittle bit functions widespread to all eukaryotes. (Link to a collection of powerallude presentations on eukaryotic cell biology.)
Origin of Eukaryotic Cells
The evolutionary jump from prokaryotes to eukaryotes is extensive and also tright here are an approximated 5000 genes found in eukaryotes that are not discovered in prokaryotes (1). The initially eukaryotic organisms likely resembled what we would now classify as protozoa. However before, most likely no straight descendants of the early on eukaryotes currently exist and the route from prokaryotes to eukaryotes is likely littered through several missing links. Two vital events in the evolution of eukaryotes are most likely the breakthrough of internal cytoskeletal device and phagotrophy.
A significant distinction in between eukaryotes and also prokaryotes is the rigid murein, or peptidoglycan, cell wall of bacteria. Although, many type of eukaryotes exhibit cell walls, they are essentially various than those of bacteria and are most likely acquired secondarily after the formation of the eukaryotes. For instance, cell walls of plant cells are composed mostly of cellushed and also fungal cell walls and cyst wall surfaces in many protozoa are written primarily of chitin. The rigidity and also toughness offered by cell walls protects cells versus mechanical stress and also confers osmotic stcapacity. Hence, cooccurrence through the loss of the murein cell wall in the early eukaryote was the advance of endocytoskeletal units based on actin and also tubulin to compensate for the loved one fragility of a naked plasma membrane. In enhancement, the early eukaryotes likely evolved in a benthic atmosphere and in specific in dense marine microbial mats. The organic solutes excreted by the bacteria and also the high salt concentration of such an atmosphere would have had an osmoprotective result. The thick microbial mats would also administer an atmosphere in which prey was very plentiful and also phagocytosis can have actually developed without reliable cellular motility.
The ancestral eukaryote most likely attached to prey using cell surface N-connected glycoproteins that developed after the loss of the murein cell wall and then digested them externally by secreting hydrolytic enzymes. To make the procedure more efficient the primitive predators might have increasingly surrounded their prey until the prey were totally engulfed in hold membranes with digestion being carried out internally within phagosomes. This endocytic system would certainly additionally call for the advance of an exocytic system to maintain the surconfront area of the plasma membrane. Hence, the advancement of phagocytosis not only included an expansion of the feature of the actin cytoskeleton however additionally drove the breakthrough of membrane trafficking and subcellular compartments including the nucleus.
The advancement of phagotrophy and endomembranes not just opened up a new method of eating, yet also allowed for endosymbiosis and the enslavement of mitochondria. An early eukaryote most likely engulfed an alpha-proteobacteria and also formed a symbiotic relationship which evolved into an assimilation of the aerobic metabolism of this organism and the breakthrough of the mitochondrion. This enslavement of the mitochondrion was more than likely one more key event in the evolution of the eukaryotes considering that extant eukaryotes are obtained from mitochondria-containing ancestors. Extant anaerobic eukaryotes without mitochondria either have actually organelles obtained from mitochondria, such as mitosomes and hydrogensomes, or at least have actually nuclear genes encoding remnant mitochondrial genes. Presumably the amitochondrial eukaryotic ancestor was at a competitive disbenefit and also did not make it through in the lengthy term. Later a cyanbacterium was enslaved by the progenitor of plants and also emerged into the chloroplasts and also similarly these plant precursors were engulfed and enslaved to form the plastids found in many type of other algae and protozoa.
The cytoskeleton ongoing to evolve and also expand its features and also in certain started to play a duty in cellular motility. Many notably tubulin came to be a crucial component in flagella and also later on myosin evolved to enable for the advancement of ameboid activity and also gliding motility. This motility enabled these at an early stage eukaryotes to expand right into various other niches (eg., planktonic, terrestrial) and also for this reason this aerobic, phagotrophic and flagellated ancestral eukaryote might radiate into the varied selection of protozoa, and ultimately the various other eukaryotes, that presently exist.
TaxonomyTaxonomy, or systematics, is the scientific research of naming and classifying organisms. In enhancement to assigning hierarchical taxonomic classifications, systematics additionally attempts to location organisms into groups reflect evolutionary relationships or phylogenies. However, taxonomic criteria are frequently arbitrary and taxonomy is always changing to reflect new discoveries and interpretations. Furthermore, utilitarian features, such as form of disease, organize variety and geographical distribution, are frequently provided in the systematics of pathogenic micro-organisms. This is specifically true for protozoan taxonomy. In addition, tright here is some dispute on the in its entirety viewpoint in the classification of protozoa and the relationships between many type of protozoan groups are not well-known (view D.J. Patterson in Am. Nat. 154, S96-124). The classification of protozoa is even more facility by the original interpretation of protozoa being unicellular heterotrophs. It is currently known that protozoa (or protists) have the right to use multiple nutritional strategies and cannot be pertained to as simply either plant-like (autotroph) or animal-like (heterotroph). Therefore, the term protozoa cannot be regarded as a true taxonomic group. In spite of the fact that the word protozoa per se is no much longer a correct taxonomic name, it is still a advantageous and also useful term. Historically protozoa were separated right into four significant groups: the ameba, the flagellates, the ciliates, and the sporozoa. The differentiating functions in between the groups was based upon motility (i.e., ameboid, flagella, cilia). The sporozoa were a heterogeneous group that developed spores in the time of one phase of their life cycles and also showed a "gliding" motility. However, such a classification scheme is fairly arbitrary and also does not necessarily reflect true evolutionary relationships in between organisms. One trouble via making use of motility as a taxonomic criteria is that many type of protozoa utilize different types of motility throughout various stperiods of their life cycles. For example, Naegleria exists in an ameba form once food is abundant and also transforms into a flagellate once food is missing. In basic, the ameba are a heterogeneous group and are all most likely dervived from flagellates. Amongst these 4 original protozoan teams only the ciliates are still taken into consideration a valid taxon. Beginning the 1960"s the electron microscopic lense was offered to recognize ultrastructural features which can serve as criteria for grouping protozoa. In many kind of situations morphology leads to a classification which locations organisims into monophyletic teams. Monophyletic means that all of the organisms in that group are more than likely derived from a widespread ancestor. For instance, many type of of the protozoa formerly referred to as sporozoa possess subcellular structures, collectively recognized as the apical organelles, and also currently form a monophyletic team referred to as apicomplexa. However before, subcellular structures and also metabolic pathways deserve to be shed in some lineages and placing those descendants have the right to be problamatic. During the 1980"s and also continuing till present time molecular methods are being applied to taxonomy. Possible evolutionary histories and also relationships can be obtained by comparing DNA or protein sequences. Molecular sequence data has evidenced phylogenies based on various other criteria, settled some debates, and caused a couple of surprises. For example, molecular information confirms that the apicomplexa are monophyletic, and furthermore, suggests that they are concerned the ciliates and dinoflagellates. These three teams are now linked into a bigger monophyletic group referred to as alveolata. This partnership had actually been previously suspected and also the name is in recommendation to morphological structures recognized as alveolar sacs. But the use of single genes can be an untrustworthy means of determining evolutionary relationships, specifically among distantly related organisms, and molecular data have to be interpreted through caution. Since the mid-1980’s classification of protists has actually been in a state of flux and also afflicted with some thoughtful controversies. On one hand, tright here is some argument for retaining facets of the Bütschlian scheme based upon motility due to its familiarity and also simplicity. However, these schemes are often in problem with phylohereditary information. In addition, the hierarchies and ranks of the standard Linnaean systematics (i.e., phylum, class, order, family members, genus, species) does not constantly fit well through micro-organisms, and also it is regularly challenging to decide which hierarchial level is many proper for any type of specific protozoan group. Previously many type of taxonomic schemes have actually characterized 5 kingdoms of life: prokaryotes (bacteria), protists, plants, fungi, and pets. In these schemes the protozoa are component of the Protista in addition to unicellular algae, diatoms, oomycetes and slime molds. However before, tright here has actually constantly been dissatisfaction via the protist team. This is in part due to protista being characterized in part by negative criterion. In other words, organisms that execute not fit in the other 4 kingdoms are defaulted right into the protista. In enhancement, some protists are phylogenetically more very closely pertained to the various other three eukaryotic kingdoms than to various other protists, and thus the protists are plainly polyphyletic. Cavalier-Smith proposes five eukaryotic kingdoms consisting of the basal, and also hence paraphyletic, kingdom Protozoa and also 4 derived kingdoms: Animalia, Fungi, Plantae, and also Chromista (Figure). A few of the former protista are now consisted of in the derived kingdoms that they are the majority of closely regarded bring about the kingdom Protozoa coming to be monophyletic. However, the alveolates, which encompass many kind of standard protozoa such as the apicomplexa, ciliates, and dinoflagellates, create a clade with the chromista, however are nonethemuch less placed in the protozoan kingdom. Hence the chromista are not holophyletic. Moving the alveolates right into a brand-new kingdom referred to as Chromalveolata would fix this problem. However before, this would most likely lead to debate and also confusion given that many kind of of the alveolates have actually been long thought about to be protozoa.
|Group of eukaryotes into 5 kingdoms: protozoa (yellow), plants (green), chromista (pink), pets (blue) and also fungi (lavender). Modified from Calvaleir-Smith (2003) Eur J Protistol 39:338-348. |
LINKSWhat are Protozoa? (Top)SymbiosisMotilityReproductionTaxonomyProtozoology HomeStudy GuidesSyllabusEukaryotic Cell BiologyOther Courses and LecturesWiser HomeBosnian translation of this webpageFinnish translation of this webpageMacedonian translation of this webpagePolish Translation of this WebpageGeorgian Translation of this WebpageThese pperiods are arisen and also kept by Mark F. Wiser, thedailysplash.tv University (©2000).
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