Amoeba reproduction is by binary fission, a type of asexual reproduction incorporating mitosis and cytokinesis. Sexual reproduction e. In older classification system, Amoeba is classified under the subphylum Sarcodina , a taxonomic group within the phylum Sarcomastigophora. Members of this subphylum are characterized by being single-celled and their ability to move by protoplasmic flow or by pseudopod. However, molecular phylogenetic studies implicate that Sarcodina is not a monophyletic group, meaning its members do not have a common descent, and as such cannot be considered as a single group.
Free-living species of the Amoeba genus are found in freshwater and soil habitats. They are major predators of bacterial populations. It is a large protist as its length may reach up to 2 mm. It is non-pathogenic as there has been no known Amoeba proteus disease in humans and other animals.
Some amoeba-like protists, though, are opportunistic pathogens. Given the opportunity, they may live as a parasite inside a host and cause disease.
One of the medically-important amoebas is the Entamoeba histolytica. This species causes entamoebiasis and amebic dysentery to its human and other primate hosts.
It forms a cyst that can be transmitted through ingestion of infected water or food. When swallowed, the cyst will release the trophozoite in the digestive tract and become pathogenic.
It causes flask-shaped ulcers, and eventually, bloody diarrhea. In certain instances, it migrates to the bloodstream, and subsequently, reaches other organs e. Another is the brain-eating amoeba, Naegleria fowleri. The species lives in hot springs, warm freshwater lakes, and rivers. It can turn from a free-living state into a parasite when it enters the body of a host, e.
It enters through the nose and penetrates the nasal mucosa. Later, it migrates to the brain through the olfactory nerves. In the brain, it feeds on brain tissues, e.
The nucleus containing the genetic material, DNA, and the mitochondria, well-identified as the "powerhouse of the cell", came about. This tutorial speaks of the evolution of organelles, their diversity, and similarity Read More. It only takes one biological cell to create an organism. A single cell is able to keep itself functional through its 'miniature machines' known as organelles.
Read this tutorial to become familiar with the different cell structures and their functions Organisms employ different strategies to boost its defenses against antigens. Humans have an immune system to combat pathogens.
As expected, farmer slugs had fewer sentinel cells. The scientists wondered if this put farmers at greater risk from toxic chemicals. To test that, Brock exposed farmers and non-farmers to a toxic chemical. The farmers could still reproduce. In fact, they fared better than non-farmers. Brock now thinks that some of the bacteria carried by the farmers helped to fight off the toxic chemicals. These bacteria might break down the chemicals. So farmers have two weapons against toxic threats: sentinel cells and bacterial buddies.
Hess and Brock study naked amoebas. Payne is intrigued by those with shells. Called testate TESS-tayt amoebas, these crafty microbes can fashion many types of shells. Those coverings can resemble discs, bowls — even vases. Many testate amoebas live in habitats called peat bogs.
These sites are usually soggy and acidic. But during summers, the peat can dry out. Not just curiosities, these peat-dwelling amoebas may play an important role in the environment, Payne says. Partly decayed plants build up in peat bogs. Bacteria eat those plants, releasing carbon-dioxide gas.
In the atmosphere, that greenhouse gas can foster global warming. Bog amoebas eat these bacteria. Payne and his colleagues studied one peat bog in China where a wildfire had burned. Wildfires may become more frequent as the climate warms. Then the team analyzed differences between two types of testate amoebas. One makes its shell out of debris, such as sand grains and bits of plants. The other type builds a glassy shell using a mineral called silica.
In unburned patches, the scientists found similar numbers of both types of amoebas. But burned patches contained many more amoebas with shells made of sand and debris. The findings suggest that the fire had destroyed more of the amoebas with silica shells. Many other details about amoebas remain unknown. How many species exist? Why do some have shells? How do amoebas affect the numbers of other microbes in some parts of the environment?
How do they influence the ecosystem around them, such as plants? Scientists have enough questions about amoebas to occupy themselves for a long time. By Roberta Kwok January 17, at am. Researchers discovered a new amoeba species in Brazil. Its shape resembles the hat worn by the wizard Gandalf in The Lord of the Rings movies.
The wiggling green spheres are organisms called Viridiraptor invadens. They spend part of their lives as amoebas. Here they have taken over an algal cell. Tyler J. Biologist Debra Brock collects soil samples in Virginia. She is hoping to find the amoeba Dictyostelium discoideum , also known as Dicty. Testate amoebas have shells. This species, Arcella dentata , builds a crown-shaped shell. Explainer: CO 2 and other greenhouse gases. Classroom questions. Peat bogs contain many testate amoebas.
Climate change may alter the number and types of amoebas that live there. Animals What biologists call a species is becoming more than just a name By Jack J. Lee October 14, Environment Wildfire smoke seeds the air with potentially dangerous microbes By Megan Sever September 2, Microbes Several plant-like algae can morph into animal-like predators By Laura Allen April 23, Sorry, your blog cannot share posts by e-mail.
Sarcodina amoebas were subdivided based on the type of pseudopodia, according to a article published in the journal Protistology. However, this system of classification was not illustrative of the evolutionary relationships between the various amoebas. It was not a family tree so to speak. Molecular phylogenetics changed the course of taxonomic classification for eukaryotes especially.
Based on the analyses of SSU rDNA and other DNA sequences, eukaryotic organisms are now organized in a manner that better represents their evolutionary relationships — the phylogenetic tree, according to the Protistology article. Each lineage in a phylogenetic tree is depicted by a branched structure.
In this system, the first levels are known as "supergroups. Animals and fungi are in the group Ophiskontha. Amoeboid protists and some parasitic lineages that lack mitochondria are part of Amoebozoa. Heterotrophic protists — organisms that take in nutrients from other organisms — are part of Excavata, while plants and most other photosynthetic organisms are part of Archaeplastida, according to the Encyclopedia of Evolutionary Biology.
In addition, he noted that amoebas are also present within Rhizaria, Excavata, Opisthokonta for example, Nucleariids, which have filopodia and within the Stramenopiles for example, Labyrinthulids. Amoebas are known to cause a range of human diseases.
Amebiasis, or amoebic dysentery, is an infection caused by Entamoeba histolytica, a human intestinal parasite, according to the Centers for Disease Control and Prevention CDC.
According to the National Institutes of Health NIH , Entamoeba histolytica can invade the colon wall and cause colitis, or can cause severe diarrhea and dysentery. Though the disease can occur anywhere in the world, it is most common in tropical regions that have substandard sanitation and crowded conditions. Contact lens wearers are potentially at risk of a rare infection of the cornea called Acanthamoeba keratitis.
According to the CDC , species in the Acanthamoeba genus are free-living and are commonly found in soil, air and water. Poor contact lens hygiene practices, such as improper storage, handling and disinfection or swimming with lenses, are some of the risk factors for the disease. While the initial symptoms include redness, itchiness and blurred vision, if left untreated the infection will eventually lead to severe pain and can lead to the loss of vision, according to the CDC.
Amoebas also cause different infections of the brain. Naegleria fowleri , which has been dubbed "the brain-eating amoeba," causes primary amoebic meningoencephalitis PAM. Though the disease is rare, it is almost always fatal , according to the CDC. Early symptoms include fever and vomiting, ultimately progressing to more severe symptoms such as hallucinations and coma. Naegleria fowleri is present in warm freshwater bodies such as hot springs, lakes and rivers, or in poorly chlorinated swimming pools and contaminated, hot tap water.
These amoebas enter from the nose and travel to the brain.
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