What is Acanthamoeba?
An Acanthamoeba is a free-living amoeba found worldwide in soil, water, and air. An amoeba is a genus of protozoa, which is a unicellular microorganism belonging to the eukaryote domain. Normally, Acanthamoeba contains typical eukaryotic organelles, cytoplasm, and a single nucleus within an outer layer, called the cell membrane. Under a microscope, this amoeba appears as a tiny, spiny, oval or round microorganism that measures between ten and thirty-five micrometers in length.
The Acanthamoeba has temporary cytoskeletal projections, called pseudopodia or acanthopodia, extending from its cell membranes that allow it to move. These threadlike filaments are composed of actin, which binds with myosin near the cell membrane to cause contraction, thus allowing the Acanthamoeba to move. These small filose projections around the rim of the cell, giving it its characteristic spiky appearance.
Acanthamoeba was accidentally discovered by scientist Aldo Castellani in 1930 when the amoeba contaminated a culture of fungus Castellani was studying. He named the amoeba Hartmannella castellani. Later, as the Hartmannella genus was split into three further categories, or genera: Acanthamoeba, Hartmannella, and Glaeseriaem>. Characteristics defining Acanthamoeba include appearance of spiny spindles, or acanthopodia, during mitosis, an irregular outer layer, and double walled cysts. The categorization was changed again when scientists made Acanthamoebidae its own family in the 1970s and then placed Hartmannella in another amoeboid family in the 1980s.
One of the Acanthamoeba’s somewhat distinct features is its double-walled cyst. Amoebas form cysts when they encounter harsh conditions by contracting into a ball and secreting a membrane, or two membranes in this case, to protect themselves until conditions become more favorable. The other most distinctive feature Acanthamoeba is its acanthopodia, which help the amoeba to move, stick to surfaces, and capture prey during its vegetative, or eating, stage. During this stage, the Acanthamoeba is called a trophozoite and may feed on algae, bacteria, yeasts, or other tiny organic matter.
As it eats, the Acanthamoeba grows exponentially during its trophozoite stage in order to reproduce asexually, via binary fission. In binary fission, the cell doubles in mass and replicates its DNA, or doubles its genetic material. The cell then splits its nucleus, the brain of the cell, into two equal nuclei in a process called mitosis. The large, double-nucleated cell then splits into two equal daughter cells via a process known as cytokinesis. Because the growth and reproduction of the cell places strain on the trophozoite, Acanthamoeba often undergo encystations during this period.
Though Acanthamoeba is abundantly present in almost every habitat and rarely causes infections, it is most notorious for its pathogenic qualities. The two human infections notably caused by Acanthamoeba are Acanthamoeba keratitis and granulomatous encephalitis. Granulomatous encephalitis is a rare and typically fatal infection that affects the central nervous system. It often presents with skin lesions and neurological symptoms and is usually restricted to people with compromised immune systems.
Acanthamoeba keratitis is a painful infection of the eye usually associated with the wearing of contact lenses. Several factors contribute to the likelihood of infection, including the improper cleaning of contact lenses, wearing a contact lens for excessive lengths of time, and exposure to contaminated water. Trophozoites or cysts adhere to the lenses, particularly worn soft lenses, and then bind to the cornea of the eye. Trophozoites then begin breaking down the cells of the eye with phagocytosis, a sort of “eating” process in which the Acanthamoeba envelopes matter with the help of its acanthopodia. This disease is rare and may result in blindness.
Written by Caitlin Kenney
