Amoebozoa
Amoebozoa is a diverse group of single-celled organisms characterized by their amoeboid movement and lack of a fixed shape. They are known for their ability to change their shape and engulf food particles by phagocytosis. Amoebozoa includes various species of amoebas and slime molds, and they play important roles in nutrient cycling and as predators in aquatic and soil ecosystems.
6 Key excerpts on "Amoebozoa"
eBook - ePubThe Ancestor's Tale
A Pilgrimage to the Dawn of Evolution
- Richard Dawkins(Author)
- 2016(Publication Date)
- Mariner Books(Publisher)
...Of the Amoebozoan ones, the best known are the cellular slime moulds or dictyostelids. They have been the life work of the distinguished American biologist J. T. Bonner, and what follows is largely drawn from his scientific memoir Life Cycles. Amoebozoans join. The word ‘amoeba’ is a description rather than a strict classification because many unrelated eukaryotes exhibit an amoeboid form. Nevertheless, the Amoebozoa include many of the classic amoebas, such as Amoeba proteus shown here, as well as most of the slime moulds—a few thousand known species in total. Recent molecular analysis [ 106 ] tentatively places some obscure single-celled organisms (including Collodictyon and Malawimonas) at the base of the Amoebozoa. We show this arrangement here, although it has yet to be fully confirmed. Cellular slime moulds are social amoebas. They literally blur the distinction between a social group of individuals and a single multicellular individual. In part of their life cycle, separate amoebas creep through the soil, feeding on bacteria and reproducing, as amoebas will, by dividing in two, feeding some more, then dividing again. Then, rather abruptly, the amoebas switch into ‘social mode’. They converge on aggregation centres, from which chemical attractants radiate outwards. As more and more amoebas stream in on an attraction centre, the more attractive it becomes, because more of the beacon chemical is released. It is a bit like the way planets form from aggregating debris. The more debris accumulates in a given attraction centre, the more its gravitational attraction. So after a while, only a few attraction centres remain, and they become planets. Eventually the amoebas in each major attraction centre unite their bodies to form a single multicellular mass, which then elongates into a multicellular ‘slug’. About a millimetre long, it even moves like a slug, with a definite front and back end, and is capable of steering in a coherent direction—for example towards light...
eBook - ePub- Britannica Educational Publishing, Kara Rogers(Authors)
- 2010(Publication Date)
- Britannica Educational Publishing(Publisher)
...Amoebas are readily identified by their ability to form temporary pseudopodia, which they utilize as a form of locomotion. This type of movement, called amoeboid movement, is considered to be the most primitive form of animal locomotion. In a narrower sense, the term amoeba refers to the genus Amoeba. The well-known type species, Amoeba proteus, is found on decaying bottom vegetation of freshwater streams and ponds. Amoeba (magnified). Russ Kinne/Photo Researchers There are numerous parasitic amoebas. Of six species found in the human alimentary tract, Entamoeba histolytica causes amebic dysentery. Two related free-living genera of increasing biomedical importance are Acanthamoeba and Naegleria, strains of which have been recognized as disease-causing parasites in several vertebrates, including humans. Amoebas are used extensively in cell research for determining the relative functions and interactions of the nucleus and the cytoplasm. Each amoeba contains a small mass of jellylike cytoplasm, which is differentiated into a thin outer plasma membrane, a layer of stiff, clear ectoplasm just within the plasma membrane, and a central granular endoplasm. The endoplasm contains food vacuoles, a granular nucleus, and a clear contractile vacuole. The amoeba has no mouth or anus. Instead, food is taken in and material excreted at any point on the cell surface. During feeding, extensions of cytoplasm flow around food particles, surrounding them and forming a vacuole into which enzymes are secreted to digest the particles. Oxygen diffuses into the cell from the surrounding water, and metabolic wastes diffuse from the amoeba into the surrounding water. A contractile vacuole, which removes excess water from the amoeba, is absent in most marine and parasitic species...
eBook - ePub- Simon Baker, Jane Nicklin, Caroline Griffiths(Authors)
- 2011(Publication Date)
- Taylor & Francis(Publisher)
...Species in the Amoebozoa are naked, heterotrophic cells with an absorptive nutrition. Growth in the Archaeplastida, Excavata, Chromalveolata, and Amoebozoa Growth in the unicellular species is synonymous with longitudinal binary fission, but budding and multiple fissions occur in some groups. Coenocytic, tubular or filamentous species grow by tip growth like the fungi. Other filamentous or membranous species grow by intussusception of new cells into the filament. The kinetics of growth of unicellular species are similar to those of bacteria, but in addition to estimations of growth by mass measurement, cell counts and chlorophyll content can be assessed. Rapid cell division can lead to very high cell populations, only limited by nitrogen, phosphate or silicon availability. Related topics (A1) The microbial world (C7) Composition of a typical prokaryotic cell (C9) Cell division (H2) Eukaryotic cell structure (H3) Cell division and ploidy (I1) Fungal structure and growth (J2) Archaeplastida, Excavata, Chromalveolata, and Amoebozoa: nutrition and metabolism (J4) Archaeplastida, Excavata, Chromalveolata, and Amoebozoa: beneficial effects Taxonomy of the Archaeplastida, Excavata, Chromalveolata, and Amoebozoa In the past the eukaryotic photosynthetic and nonphotosynthetic microorganisms were divided into form groups, the algae and the protozoa, based on the presence or absence of chloroplasts. The algae were further subdivided into groups based on pigmentation, the number and type of flagella, and other structural characteristics. Protozoa were divided on similar structural characteristics into four polyphyletic form groups, the ciliates, flagellates, sporozoans, and amebas. Advances in molecular biology now allow us to begin to create a monophyletic taxonomy of the eukaryotic microorganisms and such a scheme includes many former members of the algae, fungi, and protista. Monophyletic groups are also called clades and are considered to be the only ‘natural’ kind of group...
eBook - ePubThorp and Covich's Freshwater Invertebrates
Ecology and General Biology
- James H. Thorp, D. Christopher Rogers, James H. Thorp, D. Christopher Rogers(Authors)
- 2014(Publication Date)
- Academic Press(Publisher)
...These include: (1) the stramenopiles, a group containing organisms as morphologically and functionally dissimilar as chrysomonad flagellates and diatoms; and (2) the alveolates, a group that embraces the dinoflagellates, the ciliates, and a large group of exclusively intracellular parasites (the apicomplexans) (Adl et al., 2012). In the next sections, we focus on the broad morphological–functional groups of free-living protozoa. FIGURE 7.2 A selection from the variety of form and function in ameboid protozoa and slime molds. (a) An actinophryid heliozoon (Actinophrys ; diameter ∼0.1 mm) ingesting a flagellate. (b) A benthic foraminiferan (Rotalia) trapping diatoms and bacteria in its reticulopodial net. (c) A naked ameba (Amoeba) using pseudopodia to trap a flagellate. (d) A polycystine radiolarian (Heliosphaera ; spherical body ∼0.3 mm) with symbiotic dinoflagellates and an entrapped tintinnid ciliate. (e) Polymorphic life cycles of dictyostelid slime molds (e.g., Polysphondylium ; outer circle) and myxomycete slime molds (e.g., Physarum ; inner circle). (f) Testate ameba (Assulina ; ∼0.08 mm) with its prey (an algal cell) caught on a sticky filopodium. Ameboid Protozoa Rhizopod amebae use pseudopodia (cytoplasmic protrusions) for locomotion and feeding. There are two large groups (Figures 7.1 and 7.2): the “naked amebae” (e.g., Acanthamoeba, Vannella, Amoeba, and Vampyrella) and the shelled “testate amebae” (e.g., Arcella, Nebela, and Euglypha). Most rhizopod amebae feed nonselectively by engulfing diatoms and other algae, unicellular and filamentous cyanobacteria, detritus, and bacteria. However, there are notable variants: Vampyrella dissolves a hole in the cell wall of a green alga or desmid and then enters through the hole to digest the cytoplasm of the prey...
eBook - ePub- Dongyou Liu, Dongyou Liu(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
...Part A: Protozoa 49 Acanthamoeba castellanii Abdul Mannan Baig Contents 49.1 Introduction 49.2 Classification 49.3 Life Cycle 49.3.1 Trophozoites 49.3.2 Encysted Stage 49.4 Biology 49.5 Epidemiology 49.6 Clinical Features 49.7 Pathogenesis 49.8 Diagnosis 49.9 Treatment and Management 49.10 Prevention and Prophylaxis 49.11 Conclusion and Future Perspectives Acknowledgments References 49.1 Introduction Free-living amoebae (FLA) belonging to the Acanthamoeba and Sappinia genera, including Balamuthia mandrillaris and Naegleria fowleri species, are mitochondriate and aerobic unicellular eukaryotic protists (1). Acanthamoeba and the other FLA thrive in the natural environment as free-living organisms, but can intermittently invade the host and cause diseases. Acanthamoeba is a protist (plant-like) unicellular eukaryote, which is at an evolutionary distance of. over a billion years from Homo sapiens (2). The term Acanth precedes the name amoeba to indicate the presence of thorn-like projections on the surface of these organisms, now known as acanthopodia. FLA have caught attention worldwide, in general, and in the scientific community, in particular, because of the morbidity and mortality rates associated with the infections caused by them in humans (3). Several species of Acanthamoeba (i.e., A. castellanii, A. culbertsoni, A. hatchetti, A. polyphaga, A. rhysodes) are known to cause disease in humans and animals (4, 5). Acanthamoeba as an FLA was first reported by Castellani in 1930 who reported the presence of an amoeba in a culture of the Cryptococcus pararoseus that is a fungus. Culbertson et al. later in 1959 demonstrated the pathogenic potential of these FLA by exhibiting their ability to produce cytolytic effects on monkey kidney cells in vitro, and to kill laboratory animals in vivo...
- Michael D. Breed(Author)
- 2017(Publication Date)
- Academic Press(Publisher)
...Chapter 75 2000 Social Amoebas and Their Genomes Abstract Social amoebas cooperate, compete, and cheat. Genomics gives us a window into the evolution and regulation of these behaviors. Keywords Social amoebas; genomics; social behavior J. E. Strassmann The Concept Social amoebas cooperate, compete, and cheat. Genomics gives us a window into the evolution and regulation of these behaviors. The Explanation Slime molds, Dictyostelium discoideum, which are really social amoebas, came to the forefront of research on social behavior with the publication of Strassmann et al.’s (2000) analysis of amoeba social behavior. They showed that when a group of amoebas come together to form what is called a slug, some of the amoebas serve to be parts of the nonreproductive stalk, while others migrate to reproductive positions. In other words, there are altruistic amoebas that sacrifice themselves so that other amoebas can reproduce. In further analyses, they found that some amoebas can be “cheaters,” exploiting the altruism of others (Fig. 75.1). Figure 75.1 The social amoeba, Dictyostelium discoideum, has a complex life cycle including solitary, sexual, and social phases. This diagram highlights the social phase, in which solitary amoebas aggregate, form a slug, then a stalk, and finally a fruiting body. Following shortly after Strassmann et al.’s (2000) paper on slime mold social behavior came the thorough analysis of the genome of the social amoeba (Eichinger et al., 2005). Genomics has long held the potential for revolutionizing the study of animal behavior, and genome sequences are available for a wide variety of organisms. The social amoeba stands as a prime example of the potential for genomics can inform our understanding of social behavior. Honeybees hold similar potential (Weinstock et al., 2006), and as genomes for more animals become available, comparative genomics will yield insights into how behaviors evolved and how they are organized...
