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Biological Responses in Context
Published in Arthur T. Johnson, Biology for Engineers, 2019
When their food supply is exhausted, slime mold amoebae send out a 2 s pulsed release of cyclic adenosine monophosphate (cAMP). Low concentrations of cAMP (see Section 4.4.1, Sensors) cause a clumping of cells, whereas high concentrations produce both the attraction of cells (chemotaxis) and the release of their own pulses of cAMP upon receiving the first pulse. Following this release, there is a refractory period of at least 2 min during Ih the amoeba is not sensitive to further pulses. This guarantees that the amoeba cannot be stimulated by its own signal or that reflected back from its neighbors (Lewis and Gower, 1980). The aggregated amoebae migrate for a short distance as a single unit, and then form a fruiting body to form asexual spores (Figure 6.19.3).
Microbiological Quality of Environmental Samples
Published in Maria Csuros, Csaba Csuros, Klara Ver, Microbiological Examination of Water and Wastewater, 2018
Maria Csuros, Csaba Csuros, Klara Ver
Amoebas move by extending usually blunt, lobe-like projections of the cytoplasm called pseudopods. Any number of pseudopods can flow from one side of the amoeba cell, and the rest of the cell will flow toward the pseudopods. Amoebic dysentery or amoebiasis is found worldwide and is spread by food and water contaminated by cysts of the protozoan Entamoeba histolytica. Although stomach acid can destroy vegetative cells, it does not affect the cysts. It causes severe dysentery and the feces contain blood and mucus (the vegetative form feed on red blood cells). In severe cases, the intestinal wall is perforated and invasion of other organs (for example, the liver) is possible. The major source of amoebiasis is drinking water contamination by sewage, the fecal-oral route, and consumption of uncooked polluted vegetables. Trophozoites of E. histolytica are shown in Figures 7.4 and 7.5.
Biological Profiles in Drinking Water
Published in Edwin E. Geldreich, Microbial Quality of Water Supply in Distribution Systems, 2020
Amoebas are single-cellular microscopic animals that range from 10 to 30 µm or more in diameter. Their life cycle consists of an adult form that is a naked mass of oozing protoplasm that engulfs food and a resting stage that forms cysts that are resistant to adverse environmental conditions. Ciliates are another group of protozoans that are generally free-living but differ from amoebas in possessing cilia (hairlike feelers) for movement and rudimentary mouths for intake of solid food particles and have nuclei of two kinds. Both groups of protozoans ingest bacteria, algae, and other protozoans as food sources with digestion of these captured organisms occurring in vacuoles.
Occurrence, molecular diversity and pathogenicity of Acanthamoeba spp. isolated from aquatic environments of Northeastern Brazil
Published in International Journal of Environmental Health Research, 2022
Yrna Lorena Matos de Oliveira, Erica Tirzah Santos Lima, Marilise Brittes Rott, Roberta Pereira Miranda Fernandes, Sona Jain, Marcus Vinicius de Aragão Batista, Silvio Santana Dolabella
It is known that an intrinsic factor involved in the pathogenic potential of Acanthamoeba is the presence and production of proteases, which are important for the development of infection (Alfieri et al. 2000). Of the isolates tested in this study to determine the proteolytic activity, only one showed higher protease activity. However, it is not known whether the secretion profile of these proteolytic enzymes is a characteristic of certain isolates or can be modulated by contact with the host or other pathogenicity activating factors (Walochnik et al. 2000; Khan 2001). However, further tests, including cell culture assays and in vivo studies, are needed to evaluate the pathogenicity of the amoeba isolates.
Hydrogen bonded configurations in liquid water and their correlations with local tetrahedral structures
Published in Molecular Physics, 2023
Aswin V. Muthachikavil, Baoliang Peng, Georgios M. Kontogeorgis, Xiaodong Liang
Molecular simulations were performed using the iAMOEBA water model [57]. The water model belongs to the AMOEBA (Atomic Multipole Optimized Energetics for Biomolecular Applications) forcefield class. The iAMOEBA water model is a polarizable water model, and it is parameterised by both experimental and ab-initio data [57]. This water model has been reviewed extensively and is found to be able to reproduce liquid-phase properties of water like density, dielectric constant, self-diffusion coefficient, vapor-liquid equilibrium curve, and many more [26,39,44,58]. It has been also used to explore the two-state theories of water [26,56,59]. We performed NPT simulations of 2094 water molecules using the OpenMM 7.5 [60] simulation package. The system size was chosen so that the size of the simulation box is considerably larger (nearly 40 Å) than the distance beyond which the O-O pair correlation function out (around 10–12 Å) in water. The time evolution of energies and densities of the system was tracked in super-cooled simulations to ensure that we were sampling liquid configurations of the system. A crystallization event would often be indicated by a sudden drop in energy and density of the system. Trajectories generated ranged from 10 ns to 100 ns – at lower temperatures, longer trajectories were used. See table S1 in the supporting information for details of the lengths of trajectories and the number of configurations analyzed at different temperatures. Langevin integrator with a time-step of 1 femtosecond was used to perform the time integration, and to maintain the temperature of the system. Pressure was maintained using the Monte-Carlo barostat [61,62] with a coupling time of 25 time-steps. Non-bonded interactions were cut-off at 9 Å and correction terms were applied. Long-range electrostatic contributions were calculated using the Particle Mesh Ewald method [63]. Periodic boundary conditions were applied in all directions. The molecular trajectories were read and analysed using the MDAnalysis library [64].